Did the CoRot space find anything?

COROT-7b was found by observing its parent star's periodic decrease in apparent magnitude caused by the planet's transit in front of the star as seen from Earth. Measuring this dip in brightness, together with a size estimate for the star, allows one to calculate the planet's size. (See Transit method.) The space mission COROT observed the star COROT-7, in the stellar field LRa01, from 15 October 2007 to 3 March 2008. During this period, 153 periodic transit signals of 1.3 h duration with a depth of 3.4 × 10 were registered. After 40 days of data acquisition, the Alarm mode pipeline algorithm detected the shallow signal of COROT-7b, starting the follow-up observations from the ground to get a confirmation of the planetary nature of the transiting object.

COROT-7b

COROT-7b (previously named COROT-Exo-7b) is an exoplanet orbiting around the star COROT-7, in the constellation Monoceros, at 489 light years from Earth. It was first detected photometrically by the French-led COROT mission and reported in February 2009. Until the announcement of Kepler-10b in January 2011, it was the smallest exoplanet to have its diameter measured, at 1.58 times that of the Earth (which would give it a volume 3.95 times Earth's), and the first potential extrasolar terrestrial planet to be found. The planet has a very short orbital period, revolving around its host star in about 20 hours.

The discovery of COROT-7b was announced a year later on 3 February 2009, during the COROT Symposium 2009 in Paris. It was published in a special issue of the journal "Astronomy and Astrophysics" dedicated to results from COROT.

After the detection of COROT-7b in the lightcurve, follow-up observations carried out with a network of ground-based telescopes ruled out nearly completely the possibility of a false positive detection. The HARPS spectrograph was subsequently used to measure the mass of COROT-7b with the radial velocity method. The strong activity of the host star, which perturbates radial velocity measurements, made the mass determination troublesome.

The discovery paper, by Queloz "et al.", weighed the planet at about 4.8 Earth masses, giving it a density of 5.6 ± 1.3 g cm, similar to Earth's. The value was obtained using a pre-whitening procedure and harmonic decomposition. It was also inferred that there was a second non-transiting planet in the system, COROT-7c, with a 3.7-day orbital period.

A second paper, by Hatzes "et al.", employing Fourier analysis, reported a likely mass of 6.9 Earth masses for COROT-7b, and found hints for the presence of a third planet in the system, COROT-7d, with mass similar to Neptune's and a 9-day orbital period.

Pont "et al." evidences larger-than-declared systematic errors in the HARPS measurements, weighing COROT-7b between one and four Earth masses. The radial velocity confirmation of the planet is in shaky ground too, with a tentative detection of only 1.2 sigma certainty.

Boisse "et al.", employing simultaneous fitting of stellar activity and planetary signals in the radial velocity data, calculate for COROT-7b a mass of 5.7 Earth masses, though with a very large uncertainty.

The COROT team then published a second paper on COROT-7b's mass, removing stellar activity through analysis only of radial velocity data for which multiple measurements were taken in a given night. The planet is weighed at 7.42 Earth masses, yielding an average density of 10.4 ± 1.8 g cm, far higher than the Earth's and similar to that of the second rocky planet found, Kepler-10b.

A last study by Ferraz-Mello "et al." improved the approach used in the discovery paper, finding that it downsized the amplitude of the planets' induced radial velocities. It reports for COROT-7b a heavier mass of 8 Earth masses, in agreement with the second paper published by the COROT team. Thus, CoRoT-7b may be rocky with a large iron core, with an internal structure more like Mercury than Earth.

An independent validation of COROT-7b as a planet is supplied by follow-up performed with the space based Spitzer telescope. Its observations confirmed the transits of the planet, with the same depth, at different wavelengths than the ones observed by COROT. The data then allows to validate COROT-7b as a bona-fide planet with a very high degree of confidence, independently from the noisy radial velocity data.

Although COROT-7b's mass remains uncertain, with a range between 2 and 8 Earth masses, its radius and orbital period are well known from COROT photometry: it orbits very close to its star (1/23rd the distance from the Sun to Mercury) with an orbital period of 20 hours, 29 minutes, and 9.7 seconds and has a radius of 1.58 Earth radii. COROT-7b has the shortest orbit of any planet known at the time of its discovery.

COROT-7b has a maximum surface temperature between 1800 and 2600 °C (3300 to 4700 degrees Fahrenheit). Due to the high temperature, it may be covered in lava. The composition and density of the planet, though weakly constrained, make COROT-7b a probably rocky planet, like Earth. It could belong to a class of planets that are thought to contain up to 40% water (in the form of ice and/or vapor) in addition to rock. However, the fact that it formed so close to its parent star may mean that it is depleted of volatiles. A strong possibility exists that the planet's rotation is tidally locked to the orbital period, so that temperatures and geologic conditions on the sides of the planet facing towards and away from the star may be dramatically different. Theoretical work suggests that CoRoT-7b could be a chthonian planet (the remains of a Neptune-like planet from which much of the initial mass has been removed due to close proximity to its parent star). Other researchers dispute this, and conclude COROT-7b was always a rocky planet and not the eroded core of a gas or ice giant, due to the young age of the star system.

Any departure from circularity of its orbit (due to the influence of host star and neighboring planets) could generate intense volcanic activity similar to that of Io, via tidal heating.

A detailed study of the extreme properties of COROT-7b has been published, concluding that, despite the mass uncertainty, the planet is Earth-like in composition. The extreme proximity to the star should prevent the formation of a significant atmosphere, with the dayside hemisphere as hot as the tungsten filament of an incandescent bulb, resulting in the formation of a lava ocean. The researchers propose to name this new class of planets, COROT-7b being the first of them, "lava-ocean planets".

The uncertainty in COROT-7b mass does not allow precise modelling of the planet structure. Nevertheless, educated guesses could still be put forth. Assuming a 5-Earth-masses planet, the planet was modeled to have convection in the mantle with a small core with no more than 15% the mass of the planet, or 0.7 M. The lower mantle above the core-mantle boundary has more sluggish convection than the upper mantle because the greater pressure causes fluids to become more viscous. The temperature of the upper convecting mantle is different from one side of the planet to the other with lateral temperature differences for downwellings up to several hundred kelvins. However, the temperature of the upwelling is unaffected by downwelling and surface temperature variations. On the permanent dayside of the tidally locked planet where the surface temperature is hot from continuously facing its sun, the surface takes part in convection, which is the evidence that all the surface of this hemisphere being covered in oceans of lava. On the permanent nightside, the surface is cool enough for the formation of the crust with pools of lava above the convective mantle with intense volcanism. The dayside of the planet has larger convection cells than the nightside. Researchers also investigated the physical state of the interior of CoRoT-7b, indicating as likely a solid iron core, thus a self-generated magnetic field should be absent on the planet.

Due to the high temperatures on the illuminated side of the planet, and the likelihood that all surface volatiles have been depleted, silicate rock vaporization may have produced a tenuous atmosphere (with a pressure approaching 1 Pa or 10 mbar at 2500 K) consisting predominantly of sodium, O, O and silicon monoxide, as well as smaller amounts of potassium and other metals. Magnesium (Mg), aluminium (Al), calcium (Ca), silicon (Si), and iron (Fe) may rain out from such an atmosphere on the planet's daylight side in the form of particles of minerals, such as enstatite, corundum and spinel, wollastonite, silica, and iron (II) oxide, that would condense at altitudes below 10 km. Titanium (Ti) may be depleted (and possibly iron similarly) by being transported towards the night side before condensing as perovskite and geikelite. Sodium (and to a lesser extent, potassium), being more volatile, would be less subject to condensation into clouds, and would dominate the outer layers of the atmosphere. Observations carried out with the UVES spectrograph on COROT-7b in and out of transit, searching for emission and absorption lines originating in the exosphere of the planet, failed to detect any significative feature. Spectral lines of calcium (Ca I, Ca II) and sodium (Na), expected for a Mercury-like planet, are either absent or below detection limits, and even emission lines expected from volcanic activity, due to tidal forces exerted by the gravity of the nearby star, were not found. The lack of detections is in agreement with the previously cited theoretical work, which points to a cloudless atmosphere made of rocky vapours with a very low pressure. From the data available, scientists can only infer that COROT-7b does not resemble any of the rocky planets of the Solar System.

The star is orbited by one known extrasolar planet, designated COROT-4b.It was catalogued as part of the COROT mission to find transiting planets, when a planet was spotted using the transit method.

COROT-4

COROT-4 (formerly known as COROT-Exo-4) is a yellow-white dwarf main-sequence star in the constellation Monoceros.

Most confirmed extrasolar planets have been found using space-based telescopes (as of 01/2015). Many of the detection methods can work more effectively with space-based telescopes that avoid atmospheric haze and turbulence. COROT (2007-2012) and Kepler were space missions dedicated to searching for extrasolar planets using transits. COROT discovered about 30 new exoplanets.
Kepler (2009-2013) and K2 (2013- ) have discovered over 2000 verified exoplanets. Hubble Space Telescope and MOST have also found or confirmed a few planets. The infrared Spitzer Space Telescope has been used to detect transits of extrasolar planets, as well as occultations of the planets by their host star and phase curves.

Methods of detecting exoplanets

Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, very few of the extrasolar planets reported have been observed directly, with even fewer being resolved from their host star.

Instead, astronomers have generally had to resort to indirect methods to detect extrasolar planets. As of 2016, several different indirect methods have yielded success.

The following methods have at least once proved successful for discovering a new planet or detecting an already discovered planet:

A star with a planet will move in its own small orbit in response to the planet's gravity. This leads to variations in the speed with which the star moves toward or away from Earth, i.e. the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star's spectral lines due to the Doppler effect. The radial-velocity method measures these variations in order to confirm the presence of the planet using the binary mass function.

The speed of the star around the system's center of mass is much smaller than that of the planet, because the radius of its orbit around the center of mass is so small. (For example, the Sun moves by about 13 m/s due to Jupiter, but only about 9 cm/s due to Earth). However, velocity variations down to 1 m/s or even somewhat less can be detected with modern spectrometers, such as the HARPS (High Accuracy Radial Velocity Planet Searcher) spectrometer at the ESO 3.6 meter telescope in La Silla Observatory, Chile, or the HIRES spectrometer at the Keck telescopes.
An especially simple and inexpensive method for measuring radial velocity is "externally dispersed interferometry".

Until around 2012, the radial-velocity method (also known as Doppler spectroscopy) was by far the most productive technique used by planet hunters. (After 2012, the transit method from the Kepler spacecraft overtook it in number.) The radial velocity signal is distance independent, but requires high signal-to-noise ratio spectra to achieve high precision, and so is generally used only for relatively nearby stars, out to about 160 light-years from Earth, to find lower-mass planets. It is also not possible to simultaneously observe many target stars at a time with a single telescope. Planets of Jovian mass can be detectable around stars up to a few thousand light years away. This method easily finds massive planets that are close to stars. Modern spectrographs can also easily detect Jupiter-mass planets orbiting 10 astronomical units away from the parent star, but detection of those planets requires many years of observation. Earth-mass planets are currently detectable only in very small orbits around low-mass stars, e.g. Proxima b.

It is easier to detect planets around low-mass stars, for two reasons: First, these stars are more affected by gravitational tug from planets. The second reason is that low-mass main-sequence stars generally rotate relatively slowly. Fast rotation makes spectral-line data less clear because half of the star quickly rotates away from observer's viewpoint while the other half approaches. Detecting planets around more massive stars is easier if the star has left the main sequence, because leaving the main sequence slows down the star's rotation.

Sometimes Doppler spectrography produces false signals, especially in multi-planet and multi-star systems. Magnetic fields and certain types of stellar activity can also give false signals. When the host star has multiple planets, false signals can also arise from having insufficient data, so that multiple solutions can fit the data, as stars are not generally observed continuously. Some of the false signals can be eliminated by analyzing the stability of the planetary system, conducting photometry analysis on the host star and knowing its rotation period and stellar activity cycle periods.

Planets with orbits highly inclined to the line of sight from Earth produce smaller visible wobbles, and are thus more difficult to detect. One of the advantages of the radial velocity method is that eccentricity of the planet's orbit can be measured directly. One of the main disadvantages of the radial-velocity method is that it can only estimate a planet's minimum mass (formula_1). The posterior distribution of the inclination angle "i" depends on the true mass distribution of the planets. However, when there are multiple planets in the system that orbit relatively close to each other and have sufficient mass, orbital stability analysis allows one to constrain the maximum mass of these planets. The radial-velocity method can be used to confirm findings made by the transit method. When both methods are used in combination, then the planet's true mass can be estimated.

Although radial velocity of the star only gives a planet's minimum mass, if the planet's spectral lines can be distinguished from the star's spectral lines then the radial velocity of the planet itself can be found, and this gives the inclination of the planet's orbit. This enables measurement of the planet's actual mass. This also rules out false positives, and also provides data about the composition of the planet. The main issue is that such detection is possible only if the planet orbits around a relatively bright star and if the planet reflects or emits a lot of light.

While the radial velocity method provides information about a planet's mass, the photometric method can determine the planet's radius. If a planet crosses (transits) in front of its parent star's disk, then the observed visual brightness of the star drops by a small amount, depending on the relative sizes of the star and the planet. For example, in the case of HD 209458, the star dims by 1.7%. However, most transit signals are considerably smaller; for example, an Earth-size planet transiting a Sun-like star produces a dimming of only 80 parts per million (0.008 percent).

A theoretical transiting exoplanet light curve model predicts the following characteristics of an observed planetary system: transit depth (δ), transit duration (T), the ingress/egress duration (τ), and period of the exoplanet (P). However, these observed quantities are based on several assumptions. For convenience in the calculations, we assume that the planet and star are spherical, the stellar disk is uniform, and the orbit is circular. Depending on the relative position that an observed transiting exoplanet is while transiting a star, the observed physical parameters of the light curve will change. The transit depth (δ) of a transiting light curve describes the decrease in the normalized flux of the star during a transit. This details the radius of an exoplanet compared to the radius of the star. For example, if an exoplanet transits a solar radius size star, a planet with a larger radius would increase the transit depth and a planet with a smaller radius would decrease the transit depth. The transit duration (T) of an exoplanet is the length of time that a planet spends transiting a star. This observed parameter changes relative to how fast or slow a planet is moving in its orbit as it transits the star. The ingress/egress duration (τ) of a transiting light curve describes the length of time the planet takes to fully cover the star (ingress) and fully uncover the star (egress). If a planet transits from the one end of the diameter of the star to the other end, the ingress/egress duration is shorter because it takes less time for a planet to fully cover the star. If a planet transits a star relative to any other point other than the diameter, the ingress/egress duration lengthens as you move further away from the diameter because the planet spends a longer time partially covering the star during its transit. From these observable parameters, a number of different physical parameters (semi-major axis, star mass, star radius, planet radius, eccentricity, and inclination) are determined through calculations. With the combination of radial velocity measurements of the star, the mass of the planet is also determined.

This method has two major disadvantages. First, planetary transits are observable only when the planet's orbit happens to be perfectly aligned from the astronomers' vantage point. The probability of a planetary orbital plane being directly on the line-of-sight to a star is the ratio of the diameter of the star to the diameter of the orbit (in small stars, the radius of the planet is also an important factor). About 10% of planets with small orbits have such an alignment, and the fraction decreases for planets with larger orbits. For a planet orbiting a Sun-sized star at 1 AU, the probability of a random alignment producing a transit is 0.47%. Therefore, the method cannot guarantee that any particular star is not a host to planets. However, by scanning large areas of the sky containing thousands or even hundreds of thousands of stars at once, transit surveys can find more extrasolar planets than the radial-velocity method. Several surveys have taken that approach, such as the ground-based MEarth Project, SuperWASP, KELT, and HATNet, as well as the space-based COROT and Kepler missions. The transit method has also the advantage of detecting planets around stars that are located a few thousand light years away. The most distant planets detected by Sagittarius Window Eclipsing Extrasolar Planet Search are located near the galactic center. However, reliable follow-up observations of these stars are nearly impossible with current technology.

The second disadvantage of this method is a high rate of false detections. A 2012 study found that the rate of false positives for transits observed by the Kepler mission could be as high as 40% in single-planet systems. For this reason, a star with a single transit detection requires additional confirmation, typically from the radial-velocity method or orbital brightness modulation method. The radial velocity method is especially necessary for Jupiter-sized or larger planets, as objects of that size encompass not only planets, but also brown dwarfs and even small stars. As the false positive rate is very low in stars with two or more planet candidates, such detections often can be validated without extensive follow-up observations. Some can also be confirmed through the transit timing variation method.

Many points of light in the sky have brightness variations that may appear as transiting planets by flux measurements. Difficulties with false detections in the transit photometry method arise in three common forms: blended eclipsing binary systems, grazing eclipsing binary systems, and transits by planet sized stars. Eclipsing binary systems usually produce deep fluxes that distinguish them from exoplanet transits since planets are usually smaller than about 2R but this is not the case for blended or grain eclipsing binary systems.

Blending eclipsing binary systems are typically not physically near each other but are rather very far apart. Their blending stems from the fact that they are both lying along the same line of sight from the observer's viewpoint. The blends of extraneous stars with eclipsing binary systems can dilute the measured eclipse depth, with results often resembling the changes in flux measured for transiting exoplanets. In these cases, the target most often contains a large main sequence primary with a small main sequence secondary or a giant star with a main sequence secondary.

Grazing eclipsing binary systems are systems in which one object will just barely graze the limb of the other. In these cases, the maximum transit depth of the light curve will not be proportional to the ratio of the squares of the radii of the two stars, but will instead depend solely on the maximum area of the primary that is blocked by the secondary. Due to the reduced area that is being occulted, the measured dip in flux can mimic that of an exponent transit. Some of the false positive cases of this category can be easily found if the eclipsing binary system has circular orbit, with the two companions having difference masses. Due to the cyclic nature of the orbit, there would be two eclipsing events, one of the primary occulting the secondary and vice versa. If the two stars have significantly different masses, and this different radii and luminosities, then these two eclipses would have different depths. This repetition of a shallow and deep transit event can easily be detected and thus allow the system to be recognized as a grazing eclipsing binary system. However, if the two stellar companions are approximately the same mass, then these two eclipses would be indistinguishable, thus making it impossible to demonstrate that a grazing eclipsing binary system is being observed using only the transit photometry measurements.

Finally, there are two types of stars that are approximately the same size as gas giant planets, white dwarfs and brown stars. This is due to the fact that gas giant planets, white dwarfs, and brown dwarfs, are all supported by degenerate electron pressure. the light curve does not discriminate between objects as it only depends on the size of the transiting object. When possible, radial velocity measurements are used to verify that the transiting or eclipsing body is of planetary mass, meaning less than 13M. Transit Time Variations can also determine M. Doppler Tomography with a known radial velocity orbit can obtain minimum M and projected sing-orbit alignment.

Red giant branch stars have another issue for detecting planets around them: while planets around these stars are much more likely to transit due to the larger star size, these transit signals are hard to separate from the main star's brightness light curve as red giants have frequent pulsations in brightness with a period of a few hours to days. This is especially notable with subgiants. In addition, these stars are much more luminous, and transiting planets block a much smaller percentage of light coming from these stars. In contrast, planets can completely occult a very small star such as a neutron star or white dwarf, an event which would be easily detectable from Earth. However, due to the small star sizes, the chance of a planet aligning with such a stellar remnant is extremely small.
The main advantage of the transit method is that the size of the planet can be determined from the lightcurve. When combined with the radial-velocity method (which determines the planet's mass), one can determine the density of the planet, and hence learn something about the planet's physical structure. The planets that have been studied by both methods are by far the best-characterized of all known exoplanets.

The transit method also makes it possible to study the atmosphere of the transiting planet. When the planet transits the star, light from the star passes through the upper atmosphere of the planet. By studying the high-resolution stellar spectrum carefully, one can detect elements present in the planet's atmosphere. A planetary atmosphere, and planet for that matter, could also be detected by measuring the polarization of the starlight as it passed through or is reflected off the planet's atmosphere.

Additionally, the secondary eclipse (when the planet is blocked by its star) allows direct measurement of the planet's radiation and helps to constrain the planet's orbital eccentricity without needing the presence of other planets. If the star's photometric intensity during the secondary eclipse is subtracted from its intensity before or after, only the signal caused by the planet remains. It is then possible to measure the planet's temperature and even to detect possible signs of cloud formations on it. In March 2005, two groups of scientists carried out measurements using this technique with the Spitzer Space Telescope. The two teams, from the Harvard-Smithsonian Center for Astrophysics, led by David Charbonneau, and the Goddard Space Flight Center, led by L. D. Deming, studied the planets TrES-1 and HD 209458b respectively. The measurements revealed the planets' temperatures: 1,060 K (790°C) for TrES-1 and about 1,130 K (860 °C) for HD 209458b. In addition, the hot Neptune Gliese 436 b is known to enter secondary eclipse. However, some transiting planets orbit such that they do not enter secondary eclipse relative to Earth; HD 17156 b is over 90% likely to be one of the latter.

A French Space Agency mission, CoRoT, began in 2006 to search for planetary transits from orbit, where the absence of atmospheric scintillation allows improved accuracy. This mission was designed to be able to detect planets "a few times to several times larger than Earth" and performed "better than expected", with two exoplanet discoveries (both of the "hot Jupiter" type) as of early 2008. In June 2013, CoRoT's exoplanet count was 32 with several still to be confirmed. The satellite unexpectedly stopped transmitting data in November 2012 (after its mission had twice been extended), and was retired in June 2013.

In March 2009, NASA mission Kepler was launched to scan a large number of stars in the constellation Cygnus with a measurement precision expected to detect and characterize Earth-sized planets. The NASA Kepler Mission uses the transit method to scan a hundred thousand stars for planets. It was hoped that by the end of its mission of 3.5 years, the satellite would have collected enough data to reveal planets even smaller than Earth. By scanning a hundred thousand stars simultaneously, it was not only able to detect Earth-sized planets, it was able to collect statistics on the numbers of such planets around Sun-like stars.

On 2 February 2011, the Kepler team released a list of 1,235 extrasolar planet candidates, including 54 that may be in the habitable zone. On 5 December 2011, the Kepler team announced that they had discovered 2,326 planetary candidates, of which 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Compared to the February 2011 figures, the number of Earth-size and super-Earth-size planets increased by 200% and 140% respectively. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars, marking a decrease from the February figure; this was due to the more stringent criteria in use in the December data. By June 2013, the number of planet candidates was increased to 3,278 and some confirmed planets were smaller than Earth, some even Mars-sized (such as Kepler-62c) and one even smaller than Mercury (Kepler-37b).

The Transiting Exoplanet Survey Satellite launched in April, 2018.

Short-period planets in close orbits around their stars will undergo reflected light variations because, like the Moon, they will go through phases from full to new and back again. In addition, as these planets receive a lot of starlight, it heats them, making thermal emissions potentially detectable. Since telescopes cannot resolve the planet from the star, they see only the combined light, and the brightness of the host star seems to change over each orbit in a periodic manner. Although the effect is small — the photometric precision required is about the same as to detect an Earth-sized planet in transit across a solar-type star – such Jupiter-sized planets with an orbital period of a few days are detectable by space telescopes such as the Kepler Space Observatory. Like with the transit method, it is easier to detect large planets orbiting close to their parent star than other planets as these planets catch more light from their parent star. When a planet has a high albedo and is situated around a relatively luminous star, its light variations are easier to detect in visible light while darker planets or planets around low-temperature stars are more easily detectable with infrared light with this method. In the long run, this method may find the most planets that will be discovered by that mission because the reflected light variation with orbital phase is largely independent of orbital inclination and does not require the planet to pass in front of the disk of the star. It still cannot detect planets with circular face-on orbits from Earth's viewpoint as the amount of reflected light does not change during its orbit.

The phase function of the giant planet is also a function of its thermal properties and atmosphere, if any. Therefore, the phase curve may constrain other planet properties, such as the size distribution of atmospheric particles. When a planet is found transiting and its size is known, the phase variations curve helps calculate or constrain the planet's albedo. It is more difficult with very hot planets as the glow of the planet can interfere when trying to calculate albedo. In theory, albedo can also be found in non-transiting planets when observing the light variations with multiple wavelengths. This allows scientists to find the size of the planet even if the planet is not transiting the star.

The first-ever direct detection of the spectrum of visible light reflected from an exoplanet was made in 2015 by an international team of astronomers. The astronomers studied light from 51 Pegasi b – the first exoplanet discovered orbiting a main-sequence star (a Sunlike star), using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the European Southern Observatory's La Silla Observatory in Chile.

Both Corot and Kepler have measured the reflected light from planets. However, these planets were already known since they transit their host star. The first planets discovered by this method are Kepler-70b and Kepler-70c, found by Kepler.

A separate novel method to detect exoplanets from light variations uses relativistic beaming of the observed flux from the star due to its motion. It is also known as Doppler beaming or Doppler boosting. The method was first proposed by Abraham Loeb and Scott Gaudi in 2003
. As the planet tugs the star with its gravitation, the density of photons and therefore the apparent brightness of the star changes from observer's viewpoint. Like the radial velocity method, it can be used to determine the orbital eccentricity and the minimum mass of the planet. With this method, it is easier to detect massive planets close to their stars as these factors increase the star's motion. Unlike the radial velocity method, it does not require an accurate spectrum of a star, and therefore can be used more easily to find planets around fast-rotating stars and more distant stars.

One of the biggest disadvantages of this method is that the light variation effect is very small. A Jovian-mass planet orbiting 0.025 AU away from a Sun-like star is barely detectable even when the orbit is edge-on. This is not an ideal method for discovering new planets, as the amount of emitted and reflected starlight from the planet is usually much larger than light variations due to relativistic beaming. This method is still useful, however, as it allows for measurement of the planet's mass without the need for follow-up data collection from radial velocity observations.

The first discovery of a planet using this method (Kepler-76b) was announced in 2013.

Massive planets can cause slight tidal distortions to their host stars. When a star has a slightly ellipsoidal shape, its apparent brightness varies, depending if the oblate part of the star is facing the observer's viewpoint. Like with the relativistic beaming method, it helps to determine the minimum mass of the planet, and its sensitivity depends on the planet's orbital inclination. The extent of the effect on a star's apparent brightness can be much larger than with the relativistic beaming method, but the brightness changing cycle is twice as fast. In addition, the planet distorts the shape of the star more if it has a low semi-major axis to stellar radius ratio and the density of the star is low. This makes this method suitable for finding planets around stars that have left the main sequence.

A pulsar is a neutron star: the small, ultradense remnant of a star that has exploded as a supernova. Pulsars emit radio waves extremely regularly as they rotate. Because the intrinsic rotation of a pulsar is so regular, slight anomalies in the timing of its observed radio pulses can be used to track the pulsar's motion. Like an ordinary star, a pulsar will move in its own small orbit if it has a planet. Calculations based on pulse-timing observations can then reveal the parameters of that orbit.

This method was not originally designed for the detection of planets, but is so sensitive that it is capable of detecting planets far smaller than any other method can, down to less than a tenth the mass of Earth. It is also capable of detecting mutual gravitational perturbations between the various members of a planetary system, thereby revealing further information about those planets and their orbital parameters. In addition, it can easily detect planets which are relatively far away from the pulsar.

There are two main drawbacks to the pulsar timing method: pulsars are relatively rare, and special circumstances are required for a planet to form around a pulsar. Therefore, it is unlikely that a large number of planets will be found this way. Also, life "as we know it" could not survive on planets orbiting pulsars due to the intensity of high-energy radiation there.

In 1992, Aleksander Wolszczan and Dale Frail used this method to discover planets around the pulsar PSR 1257+12. Their discovery was quickly confirmed, making it the first confirmation of planets outside our Solar System.

Like pulsars, some other types of pulsating variable stars are regular enough that radial velocity could be determined purely photometrically from the Doppler shift of the pulsation frequency, without needing spectroscopy. This method is not as sensitive as the pulsar timing variation method, due to the periodic activity being longer and less regular. The ease of detecting planets around a variable star depends on the pulsation period of the star, the regularity of pulsations, the mass of the planet, and its distance from the host star.

The first success with this method came in 2007, when V391 Pegasi b was discovered around a pulsating subdwarf star.

The transit timing variation method considers whether transits occur with strict periodicity, or if there is a variation. When multiple transiting planets are detected, they can often be confirmed with the transit timing variation method. This is useful in planetary systems far from the Sun, where radial velocity methods cannot detect them due to the low signal-to-noise ratio. If a planet has been detected by the transit method, then variations in the timing of the transit provide an extremely sensitive method of detecting additional non-transiting planets in the system with masses comparable to Earth's. It is easier to detect transit-timing variations if planets have relatively close orbits, and when at least one of the planets is more massive, causing the orbital period of a less massive planet to be more perturbed.

The main drawback of the transit timing method is that usually not much can be learned about the planet itself. Transit timing variation can help to determine the maximum mass of a planet. In most cases, it can confirm if an object has a planetary mass, but it does not put narrow constraints on its mass. There are exceptions though, as planets in the Kepler-36 and Kepler-88 systems orbit close enough to accurately determine their masses.

The first significant detection of a non-transiting planet using TTV was carried out with NASA's Kepler spacecraft. The transiting planet Kepler-19b shows TTV with an amplitude of five minutes and a period of about 300 days, indicating the presence of a second planet, Kepler-19c, which has a period which is a near-rational multiple of the period of the transiting planet.

In circumbinary planets, variations of transit timing are mainly caused by the orbital motion of the stars, instead of gravitational perturbations by other planets. These variations make it harder to detect these planets through automated methods. However, it makes these planets easy to confirm once they are detected.

"Duration variation" refers to changes in how long the transit takes. Duration variations may be caused by an exomoon, apsidal precession for eccentric planets due to another planet in the same system, or general relativity.

When a circumbinary planet is found through the transit method, it can be easily confirmed with the transit duration variation method. In close binary systems, the stars significantly alter the motion of the companion, meaning that any transiting planet has significant variation in transit duration. The first such confirmation came from Kepler-16b.

When a binary star system is aligned such that – from the Earth's point of view – the stars pass in front of each other in their orbits, the system is called an "eclipsing binary" star system. The time of minimum light, when the star with the brighter surface is at least partially obscured by the disc of the other star, is called the primary eclipse, and approximately half an orbit later, the secondary eclipse occurs when the brighter surface area star obscures some portion of the other star. These times of minimum light, or central eclipses, constitute a time stamp on the system, much like the pulses from a pulsar (except that rather than a flash, they are a dip in brightness). If there is a planet in circumbinary orbit around the binary stars, the stars will be offset around a binary-planet center of mass. As the stars in the binary are displaced back and forth by the planet, the times of the eclipse minima will vary. The periodicity of this offset may be the most reliable way to detect extrasolar planets around close binary systems. With this method, planets are more easily detectable if they are more massive, orbit relatively closely around the system, and if the stars have low masses.

The eclipsing timing method allows the detection of planets further away from the host star than the transit method. However, signals around cataclysmic variable stars hinting for planets tend to match with unstable orbits. In 2011, Kepler-16b became the first planet to be definitely characterized via eclipsing binary timing variations.

Gravitational microlensing occurs when the gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned. Lensing events are brief, lasting for weeks or days, as the two stars and Earth are all moving relative to each other. More than a thousand such events have been observed over the past ten years.

If the foreground lensing star has a planet, then that planet's own gravitational field can make a detectable contribution to the lensing effect. Since that requires a highly improbable alignment, a very large number of distant stars must be continuously monitored in order to detect planetary microlensing contributions at a reasonable rate. This method is most fruitful for planets between Earth and the center of the galaxy, as the galactic center provides a large number of background stars.

In 1991, astronomers Shude Mao and Bohdan Paczyński proposed using gravitational microlensing to look for binary companions to stars, and their proposal was refined by Andy Gould and Abraham Loeb in 1992 as a method to detect exoplanets. Successes with the method date back to 2002, when a group of Polish astronomers (Andrzej Udalski, Marcin Kubiak and Michał Szymański from Warsaw, and Bohdan Paczyński) during project OGLE (the Optical Gravitational Lensing Experiment) developed a workable technique. During one month, they found several possible planets, though limitations in the observations prevented clear confirmation. Since then, several confirmed extrasolar planets have been detected using microlensing. This was the first method capable of detecting planets of Earth-like mass around ordinary main-sequence stars.

Unlike most other methods, which have detection bias towards planets with small (or for resolved imaging, large) orbits, the microlensing method is most sensitive to detecting planets around 1-10 astronomical units away from Sun-like stars.

A notable disadvantage of the method is that the lensing cannot be repeated, because the chance alignment never occurs again. Also, the detected planets will tend to be several kiloparsecs away, so follow-up observations with other methods are usually impossible. In addition, the only physical characteristic that can be determined by microlensing is the mass of the planet, within loose constraints. Orbital properties also tend to be unclear, as the only orbital characteristic that can be directly determined is its current semi-major axis from the parent star, which can be misleading if the planet follows an eccentric orbit. When the planet is far away from its star, it spends only a tiny portion of its orbit in a state where it is detectable with this method, so the orbital period of the planet cannot be easily determined. It is also easier to detect planets around low-mass stars, as the gravitational microlensing effect increases with the planet-to-star mass ratio.

The main advantages of the gravitational microlensing method are that it can detect low-mass planets (in principle down to Mars mass with future space projects such as WFIRST); it can detect planets in wide orbits comparable to Saturn and Uranus, which have orbital periods too long for the radial velocity or transit methods; and it can detect planets around very distant stars. When enough background stars can be observed with enough accuracy, then the method should eventually reveal how common Earth-like planets are in the galaxy.

Observations are usually performed using networks of robotic telescopes. In addition to the European Research Council-funded OGLE, the Microlensing Observations in Astrophysics (MOA) group is working to perfect this approach.

The PLANET (Probing Lensing Anomalies NETwork)/RoboNet project is even more ambitious. It allows nearly continuous round-the-clock coverage by a world-spanning telescope network, providing the opportunity to pick up microlensing contributions from planets with masses as low as Earth's. This strategy was successful in detecting the first low-mass planet on a wide orbit, designated OGLE-2005-BLG-390Lb.

Planets are extremely faint light sources compared to stars, and what little light comes from them tends to be lost in the glare from their parent star. So in general, it is very difficult to detect and resolve them directly from their host star. Planets orbiting far enough from stars to be resolved reflect very little starlight, so planets are detected through their thermal emission instead. It is easier to obtain images when the star system is relatively near to the Sun, and when the planet is especially large (considerably larger than Jupiter), widely separated from its parent star, and hot so that it emits intense infrared radiation; images have then been made in the infrared, where the planet is brighter than it is at visible wavelengths. Coronagraphs are used to block light from the star, while leaving the planet visible. Direct imaging of an Earth-like exoplanet requires extreme optothermal stability. During the accretion phase of planetary formation, the star-planet contrast may be even better in H alpha than it is in infrared – an H alpha survey is currently underway.

Direct imaging can give only loose constraints of the planet's mass, which is derived from the age of the star and the temperature of the planet. Mass can vary considerably, as planets can form several million years after the star has formed. The cooler the planet is, the less the planet's mass needs to be. In some cases it is possible to give reasonable constraints to the radius of a planet based on planet's temperature, its apparent brightness, and its distance from Earth. The spectra emitted from planets do not have to be separated from the star, which eases determining the chemical composition of planets.

Sometimes observations at multiple wavelengths are needed to rule out the planet being a brown dwarf. Direct imaging can be used to accurately measure the planet's orbit around the star. Unlike the majority of other methods, direct imaging works better with planets with face-on orbits rather than edge-on orbits, as a planet in a face-on orbit is observable during the entirety of the planet's orbit, while planets with edge-on orbits are most easily observable during their period of largest apparent separation from the parent star.

The planets detected through direct imaging currently fall into two categories. First, planets are found around stars more massive than the Sun which are young enough to have protoplanetary disks. The second category consists of possible sub-brown dwarfs found around very dim stars, or brown dwarfs which are at least 100 AU away from their parent stars.

Planetary-mass objects not gravitationally bound to a star are found through direct imaging as well.

In 2004, a group of astronomers used the European Southern Observatory's Very Large Telescope array in Chile to produce an image of 2M1207b, a companion to the brown dwarf 2M1207. In the following year, the planetary status of the companion was confirmed. The planet is estimated to be several times more massive than Jupiter, and to have an orbital radius greater than 40 AU.

In September 2008, an object was imaged at a separation of 330 AU from the star 1RXS J160929.1−210524, but it was not until 2010, that it was confirmed to be a companion planet to the star and not just a chance alignment.

The first multiplanet system, announced on 13 November 2008, was imaged in 2007, using telescopes at both the Keck Observatory and Gemini Observatory. Three planets were directly observed orbiting HR 8799, whose masses are approximately ten, ten, and seven times that of Jupiter. On the same day, 13 November 2008, it was announced that the Hubble Space Telescope directly observed an exoplanet orbiting Fomalhaut, with a mass no more than. Both systems are surrounded by disks not unlike the Kuiper belt.

In 2009, it was announced that analysis of images dating back to 2003, revealed a planet orbiting Beta Pictoris.

In 2012, it was announced that a "Super-Jupiter" planet with a mass about orbiting Kappa Andromedae was directly imaged using the Subaru Telescope in Hawaii. It orbits its parent star at a distance of about 55 AU, or nearly twice the distance of Neptune from the sun.

An additional system, GJ 758, was imaged in November 2009, by a team using the HiCIAO instrument of the Subaru Telescope, but it was a brown dwarf.

Other possible exoplanets to have been directly imaged include GQ Lupi b, AB Pictoris b, and SCR 1845 b. As of March 2006, none have been confirmed as planets; instead, they might themselves be small brown dwarfs.

Some projects to equip telescopes with planet-imaging-capable instruments include the ground-based telescopes Gemini Planet Imager, VLT-SPHERE, the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument, Palomar Project 1640, and the space telescope WFIRST-AFTA. The New Worlds Mission proposes a large occulter in space designed to block the light of nearby stars in order to observe their orbiting planets. This could be used with existing, already planned or new, purpose-built, telescopes.

In 2010, a team from NASAs Jet Propulsion Laboratory demonstrated that a vortex coronagraph could enable small scopes to directly image planets. They did this by imaging the previously imaged HR 8799 planets, using just a 1.5 meter-wide portion of the Hale Telescope.

Another promising approach is nulling interferometry.

It has also been proposed that space-telescopes that focus light using zone plates instead of mirrors would provide higher-contrast imaging, and be cheaper to launch into space due to being able to fold up the lightweight foil zone plate.

Light given off by a star is un-polarized, i.e. the direction of oscillation of the light wave is random. However, when the light is reflected off the atmosphere of a planet, the light waves interact with the molecules in the atmosphere and become polarized.

By analyzing the polarization in the combined light of the planet and star (about one part in a million), these measurements can in principle be made with very high sensitivity, as polarimetry is not limited by the stability of the Earth's atmosphere. Another main advantage is that polarimetry allows for determination of the composition of the planet's atmosphere. The main disadvantage is that it will not be able to detect planets without atmospheres. Larger planets and planets with higher albedo are easier to detect through polarimetry, as they reflect more light.

Astronomical devices used for polarimetry, called polarimeters, are capable of detecting polarized light and rejecting unpolarized beams. Groups such as ZIMPOL/CHEOPS and PlanetPol are currently using polarimeters to search for extrasolar planets. The first successful detection of an extrasolar planet using this method came in 2008, when HD 189733 b, a planet discovered three years earlier, was detected using polarimetry. However, no new planets have yet been discovered using this method.

This method consists of precisely measuring a star's position in the sky, and observing how that position changes over time. Originally, this was done visually, with hand-written records. By the end of the 19th century, this method used photographic plates, greatly improving the accuracy of the measurements as well as creating a data archive. If a star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit. Effectively, star and planet each orbit around their mutual centre of mass (barycenter), as explained by solutions to the two-body problem. Since the star is much more massive, its orbit will be much smaller. Frequently, the mutual centre of mass will lie within the radius of the larger body. Consequently, it is easier to find planets around low-mass stars, especially brown dwarfs.
Astrometry is the oldest search method for extrasolar planets, and was originally popular because of its success in characterizing astrometric binary star systems. It dates back at least to statements made by William Herschel in the late 18th century. He claimed that an "unseen companion" was affecting the position of the star he cataloged as "70 Ophiuchi". The first known formal astrometric calculation for an extrasolar planet was made by William Stephen Jacob in 1855 for this star. Similar calculations were repeated by others for another half-century until finally refuted in the early 20th century.
For two centuries claims circulated of the discovery of "unseen companions" in orbit around nearby star systems that all were reportedly found using this method, culminating in the prominent 1996 announcement, of multiple planets orbiting the nearby star Lalande 21185 by George Gatewood. None of these claims survived scrutiny by other astronomers, and the technique fell into disrepute. Unfortunately, changes in stellar position are so small—and atmospheric and systematic distortions so large—that even the best ground-based telescopes cannot produce precise enough measurements. All claims of a "planetary companion" of less than 0.1 solar mass, as the mass of the planet, made before 1996 using this method are likely spurious. In 2002, the Hubble Space Telescope did succeed in using astrometry to characterize a previously discovered planet around the star Gliese 876.

The space-based observatory "Gaia", launched in 2013, is expected to find thousands of planets via astrometry, but prior to the launch of "Gaia", no planet detected by astrometry had been confirmed.

SIM PlanetQuest was a US project (cancelled in 2010) that would have had similar exoplanet finding capabilities to Gaia.

One potential advantage of the astrometric method is that it is most sensitive to planets with large orbits. This makes it complementary to other methods that are most sensitive to planets with small orbits. However, very long observation times will be required — years, and possibly decades, as planets far enough from their star to allow detection via astrometry also take a long time to complete an orbit.

Planets orbiting around one of the stars in binary systems are more easily detectable, as they cause perturbations in the orbits of stars themselves. However, with this method, follow-up observations are needed to determine which star the planet orbits around.

In 2009, the discovery of VB 10b by astrometry was announced. This planetary object, orbiting the low mass red dwarf star VB 10, was reported to have a mass seven times that of Jupiter. If confirmed, this would be the first exoplanet discovered by astrometry, of the many that have been claimed through the years. However recent radial velocity independent studies rule out the existence of the claimed planet.
In 2010, six binary stars were astrometrically measured. One of the star systems, called HD 176051, was found with "high confidence" to have a planet.

In 2018, a study comparing observations from the Gaia spacecraft to Hipparcos data for the Beta Pictoris system was able to measure the mass of Beta Pictoris b, constraining it to Jupiter masses. This is in good agreement with previous mass estimations of roughly 13 Jupiter masses.

Non-periodic variability events, such as flares, can produce extremely faint echoes in the light curve if they reflect off an exoplanet or other scattering medium in the star system. More recently, motivated by advances in instrumentation and signal processing technologies, echoes from exoplanets are predicted to be recoverable from high-cadence photometric and spectroscopic measurements of active star systems, such as M dwarfs. These echoes are theoretically observable in all orbital inclinations.

An optical/infrared interferometer array doesn't collect as much light as a single telescope of equivalent size, but has the resolution of a single telescope the size of the array. For bright stars, this resolving power could be used to image a star's surface during a transit event and see the shadow of the planet transiting. This could provide a direct measurement of the planet's angular radius and, via parallax, its actual radius. This is more accurate than radius estimates based on transit photometry, which are dependent on stellar radius estimates which depend on models of star characteristics. Imaging also provides more accurate determination of the inclination than photometry does.

Radio emissions from magnetospheres could be detected with future radio telescopes. This could enable determination of the rotation rate of a planet, which is difficult to detect otherwise.

Auroral radio emissions from giant planets with plasma sources, such as Jupiter's volcanic moon Io, could be detected with radio telescopes such as LOFAR.

By looking at the wiggles of an interferogram using a Fourier-Transform-Spectrometer, enhanced sensitivity could be obtained in order to detect faint signals from Earth-like planets.

Disks of space dust (debris disks) surround many stars. The dust can be detected because it absorbs ordinary starlight and re-emits it as infrared radiation. Even if the dust particles have a total mass well less than that of Earth, they can still have a large enough total surface area that they outshine their parent star in infrared wavelengths.

The Hubble Space Telescope is capable of observing dust disks with its NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instrument. Even better images have now been taken by its sister instrument, the Spitzer Space Telescope, and by the European Space Agency's Herschel Space Observatory, which can see far deeper into infrared wavelengths than the Hubble can. Dust disks have now been found around more than 15% of nearby sunlike stars.

The dust is thought to be generated by collisions among comets and asteroids. Radiation pressure from the star will push the dust particles away into interstellar space over a relatively short timescale. Therefore, the detection of dust indicates continual replenishment by new collisions, and provides strong indirect evidence of the presence of small bodies like comets and asteroids that orbit the parent star. For example, the dust disk around the star tau Ceti indicates that that star has a population of objects analogous to our own Solar System's Kuiper Belt, but at least ten times thicker.

More speculatively, features in dust disks sometimes suggest the presence of full-sized planets. Some disks have a central cavity, meaning that they are really ring-shaped. The central cavity may be caused by a planet "clearing out" the dust inside its orbit. Other disks contain clumps that may be caused by the gravitational influence of a planet. Both these kinds of features are present in the dust disk around epsilon Eridani, hinting at the presence of a planet with an orbital radius of around 40 AU (in addition to the inner planet detected through the radial-velocity method). These kinds of planet-disk interactions can be modeled numerically using collisional grooming techniques.

Spectral analysis of white dwarfs' atmospheres often finds contamination of heavier elements like magnesium and calcium. These elements cannot originate from the stars' core, and it is probable that the contamination comes from asteroids that got too close (within the Roche limit) to these stars by gravitational interaction with larger planets and were torn apart by star's tidal forces. Up to 50% of young white dwarfs may be contaminated in this manner.

Additionally, the dust responsible for the atmospheric pollution may be detected by infrared radiation if it exists in sufficient quantity, similar to the detection of debris discs around main sequence stars. Data from the Spitzer Space Telescope suggests that 1-3% of white dwarfs possess detectable circumstellar dust.

In 2015, minor planets were discovered transiting the white dwarf WD 1145+017. This material orbits with a period of around 4.5 hours, and the shapes of the transit light curves suggest that the larger bodies are disintegrating, contributing to the contamination in the white dwarf's atmosphere.

Most confirmed extrasolar planets have been found using space-based telescopes (as of 01/2015). Many of the detection methods can work more effectively with space-based telescopes that avoid atmospheric haze and turbulence. COROT (2007-2012) and Kepler were space missions dedicated to searching for extrasolar planets using transits. COROT discovered about 30 new exoplanets.
Kepler (2009-2013) and K2 (2013- ) have discovered over 2000 verified exoplanets. Hubble Space Telescope and MOST have also found or confirmed a few planets. The infrared Spitzer Space Telescope has been used to detect transits of extrasolar planets, as well as occultations of the planets by their host star and phase curves.

The Gaia mission, launched in December 2013, will use astrometry to determine the true masses of 1000 nearby exoplanets.
CHEOPS and TESS, to be launched in 2018, and PLATO in 2024 will use the transit method.

CoRoT (French: ; English: Convection, Rotation and planetary Transits) was a space observatory mission which operated from 2006 to 2013. The mission's two objectives were to search for extrasolar planets with short orbital periods, particularly those of large terrestrial size, and to perform asteroseismology by measuring solar-like oscillations in stars. The mission was led by the French Space Agency (CNES) in conjunction with the European Space Agency (ESA) and other international partners.

CoRoT

Among the notable discoveries was COROT-7b, discovered in 2009 which became the first exoplanet shown to have a rock or metal-dominated composition.

CoRoT was launched at 14:28:00 UTC on 27 December 2006, atop a Soyuz 2.1b rocket, reporting first light on 18 January 2007. Subsequently, the probe started to collect science data on 2 February 2007. CoRoT is the first spacecraft dedicated to the detection of transiting extrasolar planets, opening the way for more advanced probes such as Kepler as well as future missions such as TESS and PLATO. It detected its first extrasolar planet, COROT-1b, in May 2007, just 3 months after the start of the observations. Mission flight operations were originally scheduled to end 2.5 years from launch but operations were extended to 2013. On 2 November 2012, CoRoT suffered a computer failure that made it impossible to retrieve any data from its telescope. Repair attempts were unsuccessful, so on 24 June 2013 it was announced that CoRoT has been retired and would be decommissioned; lowered in orbit to allow it to burn up in the atmosphere.

The CoRoT optical design minimized stray light coming from the Earth and provided a field of view of 2.7° by 3.05°. The CoRoT optical path consisted of a diameter off-axis afocal telescope housed in a two-stage opaque baffle specifically designed to block sunlight reflected by the Earth and a camera consisting of a dioptric objective and a focal box. Inside the focal box was an array of four CCD detectors protected against radiation by aluminum shielding 10mm thick. The asteroseismology CCDs are defocused by 760μm toward the dioptric objective to avoid saturation of the brightest stars. A prism in front of the planet detection CCDs gives a small spectrum designed to disperse more strongly in the blue wavelengths.

The four CCD detectors are model 4280 CCDs provided by E2V Technologies. These CCDs are frame-transfer, thinned, back-illuminated designs in a 2048 pixel by 2048 pixel array. Each pixel is 13.5 × 13.5μm in size which corresponds to an angular pixel size of 2.32 arcsec. The CCDs are cooled to. These detectors are arranged in a square pattern with two each dedicated to the planetary detection and asteroseismology. The data output stream from the CCDs are connected in two "chains". Each chain has one planetary detection CCD and one asteroseismology CCD. The field of view for planetary detection is 3.5°.
The satellite, built in the Cannes Mandelieu Space Center, had a launch mass of 630 kg, was 4.10 m long, 1.984 m in diameter and was powered by two solar panels.

The satellite observed perpendicular to its orbital plane, meaning there were no Earth occultations, allowing up to 150 days of continuous observation. These observation sessions, called "Long Runs", allowed detection of smaller and long-period planets. During the remaining 30 days between the two main observation periods, CoRoT observed other patches of sky for a few weeks long "Short Runs", in order to analyze a larger number of stars for the asteroseismic program. After the loss of half the field of view due to failure of Data Processing Unit No. 1 in March 2009, the observation strategy changed to 3 months observing runs, in order to optimize the number of observed stars and detection efficiency.

In order to avoid the Sun entering in its field of view, during the northern summer CoRoT observed in an area around Serpens Cauda, toward the galactic center, and during the winter it observed in Monoceros, in the Galactic anticenter. Both these "eyes" of CoRoT have been studied in preliminary observations carried out between 1998 and 2005, allowing the creation of a database, called COROTSKY, with data about the stars located in these two patches of sky. This allowed selecting the best fields for observation: the exoplanet research program requires a large number of dwarf stars to be monitored, and to avoid giant stars, for which planetary transits are too shallow to be detectable. The asteroseismic program required stars brighter than magnitude 9, and to cover as many different types of stars as possible. In addition, in order to optimize the observations, the fields shouldn't be too sparse – fewer targets observed – or too crowded – too many stars overlapping. Several fields have been already observed:

The spacecraft monitored the brightness of stars over time, searching for the slight dimming that happens in regular intervals when planets transit their host star. In every field, CoRoT recorded the brightness of thousands stars in the V-magnitude range from 11 to 16 for the extrasolar planet study. In fact, stellar targets brighter than 11 saturated the exoplanets CCD detectors, yielding inaccurate data, whilst stars dimmer than 16 don't deliver enough photons to allow planetary detections. CoRoT was sensitive enough to detect rocky planets with a radius two times larger than Earth, orbiting stars brighter than 14; it is also expected to discover new gas giants in the whole magnitude range.

CoRoT also studied asteroseismology. It can detect luminosity variations associated with acoustic pulsations of stars. This phenomenon allows calculation of a star's precise mass, age and chemical composition and will aid in comparisons between the sun and other stars. For this program, in each field of view there was be one main target star for asteroseismology as well as up to nine other targets. The number of observed targets have dropped to half after the loss of Data Processing Unit No. 1.

The mission began on 27 December 2006 when a Russian Soyuz 2-1b rocket lifted the satellite into a circular polar orbit with an altitude of 827 km. The first scientific observation campaign started on 3 February 2007.

Until March 2013, the mission's cost will amount to, of which 75% is paid by the French space agency CNES and 25% is contributed by Austria, Belgium, Germany, Spain, Brazil and the European Space Agency ESA.

The primary contractor for the construction of the CoRoT vehicle was CNES, to which individual components were delivered for vehicle assembly. The COROT equipment bay, which houses the data acquisition and pre-processing electronics, was constructed by the LESIA Laboratory at the Paris Observatory and took 60 to complete. The design and building of the instruments were done by the Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA) de l'Observatoire de Paris, the Laboratoire d'Astrophysique de Marseille, the Institut d'Astrophysique Spatiale (IAS) from Orsay, the Centre spatial de Liège (CSL) in Belgium, the IWF in Austria, the DLR (Berlin) in Germany and the ESA Research and Science Support Department. The 30 cm afocal telescope Corotel has been realized by Alcatel Alenia Space in the Centre spatial de Cannes Mandelieu.

Before the beginning of the mission, the team stated with caution that CoRoT would only be able to detect planets few times larger than Earth or greater, and that it was not specifically designed to detect habitable planets. According to the press release announcing the first results, CoRoT's instruments are performing with higher precision than had been predicted, and may be able to find planets down to the size of Earth with short orbits around small stars.
The transit method requires the detection of at least two transits, hence the planets detected will mostly have an orbital period under 75-day. Candidates that show only one transit have been found, but uncertainty remains about their exact orbital period.

CoRoT should be assumed to detect a small percentage of planets within the observed star fields, due to the low percentage of exoplanets that would transit from the angle of observation of the Solar System. The chances of seeing a planet transiting its host star is inversely proportional to the diameter of the planet's orbit, thus close in planets detections will outnumber outer planets ones. The transit method is also biased toward large planets, since their very depth transits are more easily detected than the shallows eclipses induced by terrestrial planets.

On 8 March 2009 the satellite suffered a loss of communication with Data Processing Unit No. 1, processing data from one of the two photo-detector chains on the spacecraft. Science operations resumed early April with Data Processing Unit No. 1 offline while Data Processing Unit No. 2 operating normally. The loss of photo-detector chain number 1 results in the loss of one CCD dedicated to asteroseismology and one CCD dedicated to planet detection. The field of view of the satellite is thus reduced by 50%, but without any degradation of the quality of the observations. The loss of channel 1 appears to be permanent.

The rate of discoveries of transiting planets is dictated by the need of ground-based, follow-up observations, needed to verify the planetary nature of the transit candidates. Candidate detections have been obtained for about 2.3% of all CoRoT targets, but finding periodic transit events isn't enough to claim a planet discovery, since several configurations could mimic a transiting planet, such as stellar binaries, or an eclipsing fainter star very close to the target star, whose light, blended in the light curve, can reproduce transit-like events. A first screening is executed on the light curves, searching hints of secondary eclipses or a rather V-shaped transit, indicative of a stellar nature of the transits. For the brighter targets, the prism in front of the exoplanets CCDs provides photometry in 3 different colors, enabling to reject planet candidates that have different transit depths in the three channels, a behaviour typical of binary stars. These tests allow to discard 83% of the candidate detections, whilst the remaining 17% are screened with photometric and radial velocity follow-up from a network of telescopes around the world. Photometric observations, required to rule out a possible contamination by a diluted eclipsing binary in close vicinity of the target, is performed on several 1 m-class instruments, but also employs the 2 m Tautenburg telescope in Germany and the 3,6 m CFHT/Megacam in Hawaii. The radial velocity follow-up allows to discard binaries or even multiple star system and, given enough observations, provide the mass of the exoplanets found. Radial velocity follow-up is performed with high-precision spectrographs, namely SOPHIE, HARPS and HIRES. Once the planetary nature of the candidate is established, high-resolution spectroscopy is performed on the host star, in order to accurately determine the stellar parameters, from which further exoplanet characteristics can be derived. Such work is done with large aperture telescopes, as the UVES spectrograph or HIRES.

Interesting transiting planets could be further followed-up with the infrared Spitzer Space Telescope, to give an independent confirmation at a different wavelength and possibly detect reflected light from the planet or the atmospheric compositions. COROT-7b and COROT-9b have already been observed by Spitzer.

Papers presenting the results of follow-up operations of planetary candidates in the IRa01, LRc01, LRa01, SRc01 fields have been published. Sometimes the faintness of the target star or its characteristics, such as a high rotational velocity or strong stellar activity, do not allow to determine unambiguously the nature or the mass of the planetary candidate.

Stars vibrate according to many different pulsation modes in much the same way that musical instruments emit a variety of sounds. Listening to an air on the guitar does not leave any doubt as to the nature of the instrument, and an experienced musician can even deduce the cords' material and tension. Similarly, stellar pulsation modes are characteristic of global stellar properties and of the internal physical conditions. Analyzing these modes is thus a way of probing stellar interiors to infer stellar chemical composition, rotation profiles and internal physical properties such as temperatures and densities. Asteroseismology is the science which studies the vibration modes of a star. Each of these modes can be mathematically represented by a spherical harmonic of degree l and azimuthal order m. Some examples are presented here below with a color scheme in which blue (red) indicates contracting (expanding) material. The pulsation amplitudes are highly exaggerated.

When applied to the Sun, this science is called helioseismology and has been ongoing for a few decades by now. The solar surface helium abundance was derived very accurately for the first time, which has definitely shown the importance of microscopic diffusion in the solar structure. Helioseismology analyses have also unveiled the solar internal rotational profile, the precise extent of the convective envelope and the location of the helium ionization zone. Despite enormous technical challenges, it was thus tempting to apply similar analyses to stars. From the ground this was only possible for stars close to the Sun such as α Centauri, Procyon, β Virginis... The goal is to detect extremely small light variations (down to 1 ppm) and to extract the frequencies responsible for these brightness fluctuations. This produces a frequency spectrum typical of the star under scrutiny. Oscillation periods vary from a few minutes to several hours depending of the type of star and its evolutionary state. To reach such performances, long observing times devoid of day/night alternations are required. Space is thus the ideal asteroseismic laboratory. By revealing their microvariability, measuring their oscillations at the ppm level, CoRoT has provided a new vision of stars, never reached before by any ground-based observation.

At the beginning of the mission, two out of four CCDs were assigned to asteroseismic observations of bright stars (apparent magnitude 6 to 9) in the so-called "sismo field" while the other CCDs were reserved for exoplanet hunting in the so-called "exo field". Albeit with a lower signal to noise ratio, interesting science on stars was also obtained from the exoplanets channel data, where the probe records several thousands of light curves from every observed field. Stellar activity, rotation periods, star spot evolution, star–planet interactions, multiple star systems are nice extras in addition to the main asteroseismic program. This exo field also turned out to be of incalculable richness in asteroseismic discoveries. During the first six years of its mission, CoRoT has observed about 150 bright stars in the "sismo field" and more than 150 000 weak stars in the "exo field". The figure shows where most of them are located in the Hertzsprung–Russell diagram together with some others observed from the ground.

Discoveries were numerous. Let us cite the first detection of solar-like oscillations in stars other than the Sun, the first detection of non-radial oscillations in red giant stars, the detection of solar-like oscillations in massive stars, the discovery of hundreds of frequencies in δ Scuti stars, the spectacular time evolution of the frequency spectrum of a Be (emission lines B) star during an outburst, the first detection of a deviation from a constant period spacing in gravity modes in an SPB (Slowly Pulsating B) star. Interpreting those results opened new horizons in our vision of stars and galaxies. In October 2009 the CoRoT mission was the subject of a special issue of "Astronomy and Astrophysics", dedicated to the early results of the probe. Below are some examples of breakthrough contributions to stellar astrophysics, based on CoRoT's data:

Above the convective core where mixing of chemicals is instantaneous and efficient, some layers can be affected by partial or total mixing during the main sequence phase of evolution. The extent of this "extra mixed zone" as well as the mixing efficiency are, however, difficult to assess. This additional mixing has very important consequences since it involves longer time scales for nuclear burning phases and may in particular affect the value of the stellar mass at the transition between those stars which end up their life as white dwarfs and those which face a final supernova explosion. The impact on the chemical evolution of the galaxy is obvious. Physical reasons for this extra-mixing are various, either a mixing induced by internal rotation or a mixing resulting from convective bubbles crossing the convective core boundary to enter the radiative zone where they finally lose their identity (overshooting), or even some other poorly known processes.Following exhaustion of hydrogen in the core, the overall stellar structure drastically changes. Hydrogen burning now takes place in a narrow shell surrounding the newly processed helium core. While the helium core quickly contracts and heats up, the layers above the hydrogen-burning shell undergo important expansion and cooling. The star becomes a red giant whose radius and luminosity increase in time. These stars are now located on the so-called red giant branch of the Hertzsprung–Russell diagram; they are commonly named "RGB stars". Once their central temperature reaches 100 10 K, helium starts burning in the core. For stellar masses smaller than about 2 M, this new combustion takes place in a highly degenerate matter and proceeds through a helium flash. The readjustment following the flash brings the red giant to the so-called red clump (RC) in the Hertzsprung-Russell diagram.

Whether RGB or RC, these stars all have an extended convective envelope favorable to the excitation of solar-like oscillations. A major success of CoRoT has been the discovery of radial and long-lived non-radial oscillations in thousands of red giants in the exo field. For each of them, the frequency at maximum power ν in the frequency spectrum as well as the large frequency separation between consecutive modes Δν could be measured, defining a sort of individual seismic passport.Massive variable main sequence stars have frequency spectra dominated by acoustic modes excited by the κ mechanism at work in layers where partial ionization of iron group elements produce a peak in opacity. In addition the most advanced of these stars present mixed modes i.e. modes with a g-character in deep layers and p-character in the envelope. Hydrogen burning takes place in a convective core surrounded by a region of varying chemical composition and an envelope mostly radiative except for tiny convective layers related to partial ionization of helium and/or iron group elements. As in lower mass stars the extent of the fully or partially mixed region located just above the convective core "(extra-mixed zone)" is one of the main uncertainties affecting theoretical modeling.

Another unexpected CoRoT discovery was the presence of solar-like oscillations in massive stars. The small convective shell related to the opacity peak resulting from the ionization of iron group elements at about 200 000 K (iron opacity peak) could indeed be responsible for the stochastic excitation of acoustic modes like those observed in our Sun.

During a 23-day observing run in March 2008, CoRoT observed 636 members of the young open cluster NGC 2264. The so-called "Christmas tree cluster", is located in the constellation Monoceros relatively close to us at a distance of about 1800 light years. Its age is estimated to be between 3 and 8 million years. At such a young age, the cluster is an ideal target to investigate many different scientific questions connected to the formation of stars and early stellar evolution. The CoRoT data of stars in NGC 2264 allow us to study the interaction of recently formed stars with their surrounding matter, the rotation and activity of cluster members as well as their distribution, the interiors of young stars by using asteroseismology, and planetary and stellar eclipses.

The stellar births and the stars' childhoods remain mostly hidden from us in the optical light because the early stars are deeply embedded in the dense molecular cloud from which they are born. Observations in the infrared or X-ray enable us to look deeper into the cloud, and learn more about these earliest phases in stellar evolution.
Therefore, in December 2011 and January 2012, CoRoT was part of a large international observing campaign involving four space telescopes and several ground-based observatories. All instruments observed about 4000 stars in the young cluster NGC 2264 simultaneously for about one month at different wavelengths. The Canadian space mission MOST targeted the brightest stars in the cluster in the optical light, while CoRoT observed the fainter members. MOST and CoRoT observed NGC 2264 continuously for 39 days. The NASA satellites Spitzer and Chandra measured at the same time the stars in the infrared (for 30 days) and the X-ray domains (for 300 kiloseconds). Ground-based observations were taken also at the same time, for example, with the ESO Very Large Telescope in Chile, the Canadian-French-Hawaiian Telescope in Hawaii, the McDonald Observatory in Texas, or the Calar Alto Observatory in Spain.

The CoRoT observations led to the discovery of about a dozen pulsating pre-main sequence (PMS) δ Scuti stars and the confirmation of the existence of γ Doradus pulsations in PMS stars. Also the presence of hybrid δ Scuti/γ Doradus pulsations was confirmed in members of NGC 2264. The CoRoT observations included also the well known pre-main sequence pulsators, V 588 Mon and V 589 Mon, which were the first discovered members of this group of stars. The precision attained in the CoRoT light curves also revealed the important role of granulation in pre-main sequence stars.

The investigation of T Tauri stars and their interaction with their circumstellar matter using CoRoT data revealed the existence of a new class, the AA Tauri type objects. Previously to the CoRoT observations, T Tauri stars were known to either show sinusoidal light variations that are caused by spots on the stellar surface, or completely irregular variability that is caused by the gas and dust disks surrounding the young stars. AA Tauri type objects show periodically occurring minima that are different in depth and width, hence are semi-regular variables. With the CoRoT observations this class of objects could be established. Exciting insights into the earliest phases of stellar evolution also come from the comparison of the variability present in the optical light to that in the infrared and the X-ray regime.

A large number of binary systems with non-radially pulsating members were observed by CoRoT. Some of them, which were eclipsing binaries with members of γ Doradus type, were discovered during CoRoT runs. The eclipse phenomenon plays a key role since global parameters can immediately follow, bringing invaluable constraints, in addition to the seismic ones, to stellar modeling.To find extra solar planets, CoRoT uses the method of transits detection. The primary transit is the occultation of a fraction of the light from a star when a celestial object, such as a planet, passes between the star and the observer. Its detection is made possible by the sensitivity of CCD to very small changes in light flux. Corot is capable of detecting changes in brightness of about 1/10,000. Scientists can thus hope finding planets with a size of approximately 2 times that of the Earth with this method, a class of planet called Super-Earth; detection of Corot-7b, whose radius is 1.7 times that of the Earth has shown that these predictions were correct. Corot takes an exposure of 32 seconds duration, each 32 seconds, but the image is not fully transmitted to Earth because the data flow would be too large. The onboard computer performs an important work of data reduction: the field around each target star, previously selected by the exoplanets team, is defined on a certain number of pixels described by a particular mask, the sum all pixels within the mask is then performed and several exposures are added (usually 16, which amounts to an integration time of about 8 minutes) before sending this information to the ground. For some stars, considered particularly of interest, data of each exposure is transmitted every 32 seconds. Such a sampling of 32s or 512s is well suited to the detection of a planetary transit that lasts from a little less than an hour to several hours.
A feature of this method is that it requires to detect at least three successive transits separated by two equal time intervals before one can consider a target as a serious candidate. A planet of orbital period "T" should at least be observed for a time interval between 2"T" and 3"T" to have a chance to detect three transits. The distance of the planet to the star ( which is characterized by "a" the semi-major axis of the elliptical orbit ) is linked to its orbital period by the second law of Kepler / Newton "a" = "T" M, using respectively as units for "a", M and "T": the distance from the Earth to the Sun (150 million km), the mass of the Sun, the orbital period of the Earth (1 year); this implies that if the observing time is less a year, for example, the orbits of the detectable planets will be significantly smaller than that of the Earth.
So, for Corot, due to the maximum duration of 6 months of observation for each star field, only planets closer to their stars than 0.3 Astronomical Units (less than the distance between the Sun and Mercury) can be detected, therefore generally not in the so-called habitable zone. The Kepler mission (NASA) has continuously observed the same field for many years and thus had the ability to detect Earth sized planets located farther from their stars.

The moderate number of exoplanets discovered by Corot (32 during the 6 years of operation), is explained by the fact that a confirmation should absolutely be provided by ground-based telescopes, before any announcement is made. Indeed, in the vast majority of cases, the detection of several transits does not mean the detection of a planet, but rather that of a binary star system, either one that corresponds to a grazing occultation of a star by the other, or that the system is close enough to a bright star (the CoRoT target) and the effect of transit is diluted by the light of this star; in both cases the decrease in brightness is low enough to be compatible with that of a planet passing in front of the stellar disk. To eliminate these cases, one performs observations from the ground using two methods: radial velocity spectroscopy and imaging photometry with a CCD camera. In the first case, the mass of the binary stars is immediately detected and in the second case one can expect to identify in the field the binary system near the target star responsible for the alert: the relative decline of brightness will be greater than the one seen by Corot which adds all the light in the mask defining the field of measurement. In consequence, the COROT exoplanet science team has decided to publish confirmed and fully characterized planets only and not simple candidate lists. This strategy, different from the one pursued by the Kepler mission, where the candidates are regularly updated and made available to the public, is quite lengthy. On the other hand, the approach also increases the scientific return of the mission, as the set of published COROT discoveries constitute some of the best exoplanetary studies carried out so far.

CoRoT discovered its first two planets in 2007: the hot Jupiters COROT-1b and COROT-2b. Results on asteroseismology were published in the same year.

In May 2008, two new exoplanets of Jupiter size, COROT-4b and COROT-5b, as well as an unknown massive celestial object, COROT-3b, were announced by ESA.

In February 2009, during the First Corot Symposium, the super-earth COROT-7b was announced, which at the time was the smallest exoplanet to have its diameter confirmed, at 1.58 Earth diameters. The discoveries of a second non-transiting planet in the same system, COROT-7c, and of a new Hot Jupiter, COROT-6b, were also announced at the Symposium.

In March 2010 COROT-9b was announced. It's a long period planet (95.3 days) in an orbit close to that of Mercury.

In June 2010 the CoRoT team announced six new planets, COROT-8b, COROT-10b, COROT-11b, COROT-12b, COROT-13b, COROT-14b, and a brown dwarf, COROT-15b. All the planets announced are Jupiter sized, except COROT-8b, which appears to be somewhat between Saturn and Neptune. The probe was also able to tentatively detect the reflected light at optical wavelengths of HD46375 b, a non-transiting planet.

In June 2011, during the Second CoRoT Symposium, the probe added ten new objects to the Exoplanet catalogue: COROT-16b, COROT-17b, COROT-18b, COROT-19b, COROT-20b, COROT-21b, COROT-22b, COROT-23b, COROT-24b, COROT-24c.

As of November 2011, around 600 additional candidate exoplanets are being screened for confirmation.

Among the exoplanets CoRoT detected, one can highlight a subset with the most original features :

The following transiting planets have been announced by the mission.

"Light green rows indicate that the planet orbits one of the stars in a binary star system."
The following table illustrates brown dwarf detected by COROT as well as non-transiting planets detected in the follow-up program:
 All Corot planets were detected during long runs "i.e." of at least 70 days. The "detection team " found on average between 200 and 300 cases of periodic events for each run, corresponding to 2–3% of the stars monitored. Of these, only 530 in total were selected as candidate planets (223 in the direction of the galactic anti-center and 307 towards the center ). Only 30 of them were finally found to be true planets, "i.e." about 6%, other cases being eclipsing binaries ( 46%) or unresolved cases (48%).

The CoRoT planets cover the wide range of properties and features found in the disparate family of exoplanets: for instance, the masses of CoRoT planets cover a range of almost four orders of magnitude, as shown on Figure.

Tracing the mass of the planet versus the mass of the star (Figure), one finds that the CoRoT data set, with its lower scatter than other experiments, indicates a clear trend that massive planets tend to orbit massive stars, which is consistent with the most commonly accepted models of planetary formation.

Among the notable discoveries was COROT-7b, discovered in 2009 which became the first exoplanet shown to have a rock or metal-dominated composition.

CoRoT

CoRoT (French: ; English: Convection, Rotation and planetary Transits) was a space observatory mission which operated from 2006 to 2013. The mission's two objectives were to search for extrasolar planets with short orbital periods, particularly those of large terrestrial size, and to perform asteroseismology by measuring solar-like oscillations in stars. The mission was led by the French Space Agency (CNES) in conjunction with the European Space Agency (ESA) and other international partners.

The CoRoT optical design minimized stray light coming from the Earth and provided a field of view of 2.7° by 3.05°. The CoRoT optical path consisted of a diameter off-axis afocal telescope housed in a two-stage opaque baffle specifically designed to block sunlight reflected by the Earth and a camera consisting of a dioptric objective and a focal box. Inside the focal box was an array of four CCD detectors protected against radiation by aluminum shielding 10mm thick. The asteroseismology CCDs are defocused by 760μm toward the dioptric objective to avoid saturation of the brightest stars. A prism in front of the planet detection CCDs gives a small spectrum designed to disperse more strongly in the blue wavelengths.

The four CCD detectors are model 4280 CCDs provided by E2V Technologies. These CCDs are frame-transfer, thinned, back-illuminated designs in a 2048 pixel by 2048 pixel array. Each pixel is 13.5 × 13.5μm in size which corresponds to an angular pixel size of 2.32 arcsec. The CCDs are cooled to. These detectors are arranged in a square pattern with two each dedicated to the planetary detection and asteroseismology. The data output stream from the CCDs are connected in two "chains". Each chain has one planetary detection CCD and one asteroseismology CCD. The field of view for planetary detection is 3.5°.
The satellite, built in the Cannes Mandelieu Space Center, had a launch mass of 630 kg, was 4.10 m long, 1.984 m in diameter and was powered by two solar panels.

The satellite observed perpendicular to its orbital plane, meaning there were no Earth occultations, allowing up to 150 days of continuous observation. These observation sessions, called "Long Runs", allowed detection of smaller and long-period planets. During the remaining 30 days between the two main observation periods, CoRoT observed other patches of sky for a few weeks long "Short Runs", in order to analyze a larger number of stars for the asteroseismic program. After the loss of half the field of view due to failure of Data Processing Unit No. 1 in March 2009, the observation strategy changed to 3 months observing runs, in order to optimize the number of observed stars and detection efficiency.

The spacecraft monitored the brightness of stars over time, searching for the slight dimming that happens in regular intervals when planets transit their host star. In every field, CoRoT recorded the brightness of thousands stars in the V-magnitude range from 11 to 16 for the extrasolar planet study. In fact, stellar targets brighter than 11 saturated the exoplanets CCD detectors, yielding inaccurate data, whilst stars dimmer than 16 don't deliver enough photons to allow planetary detections. CoRoT was sensitive enough to detect rocky planets with a radius two times larger than Earth, orbiting stars brighter than 14; it is also expected to discover new gas giants in the whole magnitude range.

CoRoT also studied asteroseismology. It can detect luminosity variations associated with acoustic pulsations of stars. This phenomenon allows calculation of a star's precise mass, age and chemical composition and will aid in comparisons between the sun and other stars. For this program, in each field of view there was be one main target star for asteroseismology as well as up to nine other targets. The number of observed targets have dropped to half after the loss of Data Processing Unit No. 1.

The mission began on 27 December 2006 when a Russian Soyuz 2-1b rocket lifted the satellite into a circular polar orbit with an altitude of 827 km. The first scientific observation campaign started on 3 February 2007.

Until March 2013, the mission's cost will amount to, of which 75% is paid by the French space agency CNES and 25% is contributed by Austria, Belgium, Germany, Spain, Brazil and the European Space Agency ESA.

The primary contractor for the construction of the CoRoT vehicle was CNES, to which individual components were delivered for vehicle assembly. The COROT equipment bay, which houses the data acquisition and pre-processing electronics, was constructed by the LESIA Laboratory at the Paris Observatory and took 60 to complete. The design and building of the instruments were done by the Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA) de l'Observatoire de Paris, the Laboratoire d'Astrophysique de Marseille, the Institut d'Astrophysique Spatiale (IAS) from Orsay, the Centre spatial de Liège (CSL) in Belgium, the IWF in Austria, the DLR (Berlin) in Germany and the ESA Research and Science Support Department. The 30 cm afocal telescope Corotel has been realized by Alcatel Alenia Space in the Centre spatial de Cannes Mandelieu.

Before the beginning of the mission, the team stated with caution that CoRoT would only be able to detect planets few times larger than Earth or greater, and that it was not specifically designed to detect habitable planets. According to the press release announcing the first results, CoRoT's instruments are performing with higher precision than had been predicted, and may be able to find planets down to the size of Earth with short orbits around small stars.
The transit method requires the detection of at least two transits, hence the planets detected will mostly have an orbital period under 75-day. Candidates that show only one transit have been found, but uncertainty remains about their exact orbital period.

CoRoT should be assumed to detect a small percentage of planets within the observed star fields, due to the low percentage of exoplanets that would transit from the angle of observation of the Solar System. The chances of seeing a planet transiting its host star is inversely proportional to the diameter of the planet's orbit, thus close in planets detections will outnumber outer planets ones. The transit method is also biased toward large planets, since their very depth transits are more easily detected than the shallows eclipses induced by terrestrial planets.

On 8 March 2009 the satellite suffered a loss of communication with Data Processing Unit No. 1, processing data from one of the two photo-detector chains on the spacecraft. Science operations resumed early April with Data Processing Unit No. 1 offline while Data Processing Unit No. 2 operating normally. The loss of photo-detector chain number 1 results in the loss of one CCD dedicated to asteroseismology and one CCD dedicated to planet detection. The field of view of the satellite is thus reduced by 50%, but without any degradation of the quality of the observations. The loss of channel 1 appears to be permanent.

Interesting transiting planets could be further followed-up with the infrared Spitzer Space Telescope, to give an independent confirmation at a different wavelength and possibly detect reflected light from the planet or the atmospheric compositions. COROT-7b and COROT-9b have already been observed by Spitzer.

Papers presenting the results of follow-up operations of planetary candidates in the IRa01, LRc01, LRa01, SRc01 fields have been published. Sometimes the faintness of the target star or its characteristics, such as a high rotational velocity or strong stellar activity, do not allow to determine unambiguously the nature or the mass of the planetary candidate.

Another unexpected CoRoT discovery was the presence of solar-like oscillations in massive stars. The small convective shell related to the opacity peak resulting from the ionization of iron group elements at about 200 000 K (iron opacity peak) could indeed be responsible for the stochastic excitation of acoustic modes like those observed in our Sun.

During a 23-day observing run in March 2008, CoRoT observed 636 members of the young open cluster NGC 2264. The so-called "Christmas tree cluster", is located in the constellation Monoceros relatively close to us at a distance of about 1800 light years. Its age is estimated to be between 3 and 8 million years. At such a young age, the cluster is an ideal target to investigate many different scientific questions connected to the formation of stars and early stellar evolution. The CoRoT data of stars in NGC 2264 allow us to study the interaction of recently formed stars with their surrounding matter, the rotation and activity of cluster members as well as their distribution, the interiors of young stars by using asteroseismology, and planetary and stellar eclipses.

The CoRoT observations led to the discovery of about a dozen pulsating pre-main sequence (PMS) δ Scuti stars and the confirmation of the existence of γ Doradus pulsations in PMS stars. Also the presence of hybrid δ Scuti/γ Doradus pulsations was confirmed in members of NGC 2264. The CoRoT observations included also the well known pre-main sequence pulsators, V 588 Mon and V 589 Mon, which were the first discovered members of this group of stars. The precision attained in the CoRoT light curves also revealed the important role of granulation in pre-main sequence stars.

The investigation of T Tauri stars and their interaction with their circumstellar matter using CoRoT data revealed the existence of a new class, the AA Tauri type objects. Previously to the CoRoT observations, T Tauri stars were known to either show sinusoidal light variations that are caused by spots on the stellar surface, or completely irregular variability that is caused by the gas and dust disks surrounding the young stars. AA Tauri type objects show periodically occurring minima that are different in depth and width, hence are semi-regular variables. With the CoRoT observations this class of objects could be established. Exciting insights into the earliest phases of stellar evolution also come from the comparison of the variability present in the optical light to that in the infrared and the X-ray regime.

CoRoT discovered its first two planets in 2007: the hot Jupiters COROT-1b and COROT-2b. Results on asteroseismology were published in the same year.

In May 2008, two new exoplanets of Jupiter size, COROT-4b and COROT-5b, as well as an unknown massive celestial object, COROT-3b, were announced by ESA.

In February 2009, during the First Corot Symposium, the super-earth COROT-7b was announced, which at the time was the smallest exoplanet to have its diameter confirmed, at 1.58 Earth diameters. The discoveries of a second non-transiting planet in the same system, COROT-7c, and of a new Hot Jupiter, COROT-6b, were also announced at the Symposium.

In March 2010 COROT-9b was announced. It's a long period planet (95.3 days) in an orbit close to that of Mercury.

In June 2010 the CoRoT team announced six new planets, COROT-8b, COROT-10b, COROT-11b, COROT-12b, COROT-13b, COROT-14b, and a brown dwarf, COROT-15b. All the planets announced are Jupiter sized, except COROT-8b, which appears to be somewhat between Saturn and Neptune. The probe was also able to tentatively detect the reflected light at optical wavelengths of HD46375 b, a non-transiting planet.

In June 2011, during the Second CoRoT Symposium, the probe added ten new objects to the Exoplanet catalogue: COROT-16b, COROT-17b, COROT-18b, COROT-19b, COROT-20b, COROT-21b, COROT-22b, COROT-23b, COROT-24b, COROT-24c.

As of November 2011, around 600 additional candidate exoplanets are being screened for confirmation.

Among the exoplanets CoRoT detected, one can highlight a subset with the most original features :

The following transiting planets have been announced by the mission.

"Light green rows indicate that the planet orbits one of the stars in a binary star system."
The following table illustrates brown dwarf detected by COROT as well as non-transiting planets detected in the follow-up program:
 All Corot planets were detected during long runs "i.e." of at least 70 days. The "detection team " found on average between 200 and 300 cases of periodic events for each run, corresponding to 2–3% of the stars monitored. Of these, only 530 in total were selected as candidate planets (223 in the direction of the galactic anti-center and 307 towards the center ). Only 30 of them were finally found to be true planets, "i.e." about 6%, other cases being eclipsing binaries ( 46%) or unresolved cases (48%).

The CoRoT planets cover the wide range of properties and features found in the disparate family of exoplanets: for instance, the masses of CoRoT planets cover a range of almost four orders of magnitude, as shown on Figure.

Tracing the mass of the planet versus the mass of the star (Figure), one finds that the CoRoT data set, with its lower scatter than other experiments, indicates a clear trend that massive planets tend to orbit massive stars, which is consistent with the most commonly accepted models of planetary formation.

CoRoT

CoRoT (French: ; English: Convection, Rotation and planetary Transits) was a space observatory mission which operated from 2006 to 2013. The mission's two objectives were to search for extrasolar planets with short orbital periods, particularly those of large terrestrial size, and to perform asteroseismology by measuring solar-like oscillations in stars. The mission was led by the French Space Agency (CNES) in conjunction with the European Space Agency (ESA) and other international partners.

Among the notable discoveries was COROT-7b, discovered in 2009 which became the first exoplanet shown to have a rock or metal-dominated composition.

The CoRoT optical design minimized stray light coming from the Earth and provided a field of view of 2.7° by 3.05°. The CoRoT optical path consisted of a diameter off-axis afocal telescope housed in a two-stage opaque baffle specifically designed to block sunlight reflected by the Earth and a camera consisting of a dioptric objective and a focal box. Inside the focal box was an array of four CCD detectors protected against radiation by aluminum shielding 10mm thick. The asteroseismology CCDs are defocused by 760μm toward the dioptric objective to avoid saturation of the brightest stars. A prism in front of the planet detection CCDs gives a small spectrum designed to disperse more strongly in the blue wavelengths.

The four CCD detectors are model 4280 CCDs provided by E2V Technologies. These CCDs are frame-transfer, thinned, back-illuminated designs in a 2048 pixel by 2048 pixel array. Each pixel is 13.5 × 13.5μm in size which corresponds to an angular pixel size of 2.32 arcsec. The CCDs are cooled to. These detectors are arranged in a square pattern with two each dedicated to the planetary detection and asteroseismology. The data output stream from the CCDs are connected in two "chains". Each chain has one planetary detection CCD and one asteroseismology CCD. The field of view for planetary detection is 3.5°.
The satellite, built in the Cannes Mandelieu Space Center, had a launch mass of 630 kg, was 4.10 m long, 1.984 m in diameter and was powered by two solar panels.

The satellite observed perpendicular to its orbital plane, meaning there were no Earth occultations, allowing up to 150 days of continuous observation. These observation sessions, called "Long Runs", allowed detection of smaller and long-period planets. During the remaining 30 days between the two main observation periods, CoRoT observed other patches of sky for a few weeks long "Short Runs", in order to analyze a larger number of stars for the asteroseismic program. After the loss of half the field of view due to failure of Data Processing Unit No. 1 in March 2009, the observation strategy changed to 3 months observing runs, in order to optimize the number of observed stars and detection efficiency.

The spacecraft monitored the brightness of stars over time, searching for the slight dimming that happens in regular intervals when planets transit their host star. In every field, CoRoT recorded the brightness of thousands stars in the V-magnitude range from 11 to 16 for the extrasolar planet study. In fact, stellar targets brighter than 11 saturated the exoplanets CCD detectors, yielding inaccurate data, whilst stars dimmer than 16 don't deliver enough photons to allow planetary detections. CoRoT was sensitive enough to detect rocky planets with a radius two times larger than Earth, orbiting stars brighter than 14; it is also expected to discover new gas giants in the whole magnitude range.

CoRoT also studied asteroseismology. It can detect luminosity variations associated with acoustic pulsations of stars. This phenomenon allows calculation of a star's precise mass, age and chemical composition and will aid in comparisons between the sun and other stars. For this program, in each field of view there was be one main target star for asteroseismology as well as up to nine other targets. The number of observed targets have dropped to half after the loss of Data Processing Unit No. 1.

The mission began on 27 December 2006 when a Russian Soyuz 2-1b rocket lifted the satellite into a circular polar orbit with an altitude of 827 km. The first scientific observation campaign started on 3 February 2007.

Until March 2013, the mission's cost will amount to, of which 75% is paid by the French space agency CNES and 25% is contributed by Austria, Belgium, Germany, Spain, Brazil and the European Space Agency ESA.

The primary contractor for the construction of the CoRoT vehicle was CNES, to which individual components were delivered for vehicle assembly. The COROT equipment bay, which houses the data acquisition and pre-processing electronics, was constructed by the LESIA Laboratory at the Paris Observatory and took 60 to complete. The design and building of the instruments were done by the Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA) de l'Observatoire de Paris, the Laboratoire d'Astrophysique de Marseille, the Institut d'Astrophysique Spatiale (IAS) from Orsay, the Centre spatial de Liège (CSL) in Belgium, the IWF in Austria, the DLR (Berlin) in Germany and the ESA Research and Science Support Department. The 30 cm afocal telescope Corotel has been realized by Alcatel Alenia Space in the Centre spatial de Cannes Mandelieu.

Before the beginning of the mission, the team stated with caution that CoRoT would only be able to detect planets few times larger than Earth or greater, and that it was not specifically designed to detect habitable planets. According to the press release announcing the first results, CoRoT's instruments are performing with higher precision than had been predicted, and may be able to find planets down to the size of Earth with short orbits around small stars.
The transit method requires the detection of at least two transits, hence the planets detected will mostly have an orbital period under 75-day. Candidates that show only one transit have been found, but uncertainty remains about their exact orbital period.

CoRoT should be assumed to detect a small percentage of planets within the observed star fields, due to the low percentage of exoplanets that would transit from the angle of observation of the Solar System. The chances of seeing a planet transiting its host star is inversely proportional to the diameter of the planet's orbit, thus close in planets detections will outnumber outer planets ones. The transit method is also biased toward large planets, since their very depth transits are more easily detected than the shallows eclipses induced by terrestrial planets.

On 8 March 2009 the satellite suffered a loss of communication with Data Processing Unit No. 1, processing data from one of the two photo-detector chains on the spacecraft. Science operations resumed early April with Data Processing Unit No. 1 offline while Data Processing Unit No. 2 operating normally. The loss of photo-detector chain number 1 results in the loss of one CCD dedicated to asteroseismology and one CCD dedicated to planet detection. The field of view of the satellite is thus reduced by 50%, but without any degradation of the quality of the observations. The loss of channel 1 appears to be permanent.

Interesting transiting planets could be further followed-up with the infrared Spitzer Space Telescope, to give an independent confirmation at a different wavelength and possibly detect reflected light from the planet or the atmospheric compositions. COROT-7b and COROT-9b have already been observed by Spitzer.

Papers presenting the results of follow-up operations of planetary candidates in the IRa01, LRc01, LRa01, SRc01 fields have been published. Sometimes the faintness of the target star or its characteristics, such as a high rotational velocity or strong stellar activity, do not allow to determine unambiguously the nature or the mass of the planetary candidate.

Discoveries were numerous. Let us cite the first detection of solar-like oscillations in stars other than the Sun, the first detection of non-radial oscillations in red giant stars, the detection of solar-like oscillations in massive stars, the discovery of hundreds of frequencies in δ Scuti stars, the spectacular time evolution of the frequency spectrum of a Be (emission lines B) star during an outburst, the first detection of a deviation from a constant period spacing in gravity modes in an SPB (Slowly Pulsating B) star. Interpreting those results opened new horizons in our vision of stars and galaxies. In October 2009 the CoRoT mission was the subject of a special issue of "Astronomy and Astrophysics", dedicated to the early results of the probe. Below are some examples of breakthrough contributions to stellar astrophysics, based on CoRoT's data:

Another unexpected CoRoT discovery was the presence of solar-like oscillations in massive stars. The small convective shell related to the opacity peak resulting from the ionization of iron group elements at about 200 000 K (iron opacity peak) could indeed be responsible for the stochastic excitation of acoustic modes like those observed in our Sun.

During a 23-day observing run in March 2008, CoRoT observed 636 members of the young open cluster NGC 2264. The so-called "Christmas tree cluster", is located in the constellation Monoceros relatively close to us at a distance of about 1800 light years. Its age is estimated to be between 3 and 8 million years. At such a young age, the cluster is an ideal target to investigate many different scientific questions connected to the formation of stars and early stellar evolution. The CoRoT data of stars in NGC 2264 allow us to study the interaction of recently formed stars with their surrounding matter, the rotation and activity of cluster members as well as their distribution, the interiors of young stars by using asteroseismology, and planetary and stellar eclipses.

The CoRoT observations led to the discovery of about a dozen pulsating pre-main sequence (PMS) δ Scuti stars and the confirmation of the existence of γ Doradus pulsations in PMS stars. Also the presence of hybrid δ Scuti/γ Doradus pulsations was confirmed in members of NGC 2264. The CoRoT observations included also the well known pre-main sequence pulsators, V 588 Mon and V 589 Mon, which were the first discovered members of this group of stars. The precision attained in the CoRoT light curves also revealed the important role of granulation in pre-main sequence stars.

The investigation of T Tauri stars and their interaction with their circumstellar matter using CoRoT data revealed the existence of a new class, the AA Tauri type objects. Previously to the CoRoT observations, T Tauri stars were known to either show sinusoidal light variations that are caused by spots on the stellar surface, or completely irregular variability that is caused by the gas and dust disks surrounding the young stars. AA Tauri type objects show periodically occurring minima that are different in depth and width, hence are semi-regular variables. With the CoRoT observations this class of objects could be established. Exciting insights into the earliest phases of stellar evolution also come from the comparison of the variability present in the optical light to that in the infrared and the X-ray regime.

CoRoT discovered its first two planets in 2007: the hot Jupiters COROT-1b and COROT-2b. Results on asteroseismology were published in the same year.

In May 2008, two new exoplanets of Jupiter size, COROT-4b and COROT-5b, as well as an unknown massive celestial object, COROT-3b, were announced by ESA.

In February 2009, during the First Corot Symposium, the super-earth COROT-7b was announced, which at the time was the smallest exoplanet to have its diameter confirmed, at 1.58 Earth diameters. The discoveries of a second non-transiting planet in the same system, COROT-7c, and of a new Hot Jupiter, COROT-6b, were also announced at the Symposium.

In March 2010 COROT-9b was announced. It's a long period planet (95.3 days) in an orbit close to that of Mercury.

In June 2010 the CoRoT team announced six new planets, COROT-8b, COROT-10b, COROT-11b, COROT-12b, COROT-13b, COROT-14b, and a brown dwarf, COROT-15b. All the planets announced are Jupiter sized, except COROT-8b, which appears to be somewhat between Saturn and Neptune. The probe was also able to tentatively detect the reflected light at optical wavelengths of HD46375 b, a non-transiting planet.

In June 2011, during the Second CoRoT Symposium, the probe added ten new objects to the Exoplanet catalogue: COROT-16b, COROT-17b, COROT-18b, COROT-19b, COROT-20b, COROT-21b, COROT-22b, COROT-23b, COROT-24b, COROT-24c.

As of November 2011, around 600 additional candidate exoplanets are being screened for confirmation.

Among the exoplanets CoRoT detected, one can highlight a subset with the most original features :

The following transiting planets have been announced by the mission.

"Light green rows indicate that the planet orbits one of the stars in a binary star system."
The following table illustrates brown dwarf detected by COROT as well as non-transiting planets detected in the follow-up program:
 All Corot planets were detected during long runs "i.e." of at least 70 days. The "detection team " found on average between 200 and 300 cases of periodic events for each run, corresponding to 2–3% of the stars monitored. Of these, only 530 in total were selected as candidate planets (223 in the direction of the galactic anti-center and 307 towards the center ). Only 30 of them were finally found to be true planets, "i.e." about 6%, other cases being eclipsing binaries ( 46%) or unresolved cases (48%).

The CoRoT planets cover the wide range of properties and features found in the disparate family of exoplanets: for instance, the masses of CoRoT planets cover a range of almost four orders of magnitude, as shown on Figure.

Tracing the mass of the planet versus the mass of the star (Figure), one finds that the CoRoT data set, with its lower scatter than other experiments, indicates a clear trend that massive planets tend to orbit massive stars, which is consistent with the most commonly accepted models of planetary formation.

CoRoT

CoRoT (French: ; English: Convection, Rotation and planetary Transits) was a space observatory mission which operated from 2006 to 2013. The mission's two objectives were to search for extrasolar planets with short orbital periods, particularly those of large terrestrial size, and to perform asteroseismology by measuring solar-like oscillations in stars. The mission was led by the French Space Agency (CNES) in conjunction with the European Space Agency (ESA) and other international partners.

Among the notable discoveries was COROT-7b, discovered in 2009 which became the first exoplanet shown to have a rock or metal-dominated composition.

The CoRoT optical design minimized stray light coming from the Earth and provided a field of view of 2.7° by 3.05°. The CoRoT optical path consisted of a diameter off-axis afocal telescope housed in a two-stage opaque baffle specifically designed to block sunlight reflected by the Earth and a camera consisting of a dioptric objective and a focal box. Inside the focal box was an array of four CCD detectors protected against radiation by aluminum shielding 10mm thick. The asteroseismology CCDs are defocused by 760μm toward the dioptric objective to avoid saturation of the brightest stars. A prism in front of the planet detection CCDs gives a small spectrum designed to disperse more strongly in the blue wavelengths.

The four CCD detectors are model 4280 CCDs provided by E2V Technologies. These CCDs are frame-transfer, thinned, back-illuminated designs in a 2048 pixel by 2048 pixel array. Each pixel is 13.5 × 13.5μm in size which corresponds to an angular pixel size of 2.32 arcsec. The CCDs are cooled to. These detectors are arranged in a square pattern with two each dedicated to the planetary detection and asteroseismology. The data output stream from the CCDs are connected in two "chains". Each chain has one planetary detection CCD and one asteroseismology CCD. The field of view for planetary detection is 3.5°.
The satellite, built in the Cannes Mandelieu Space Center, had a launch mass of 630 kg, was 4.10 m long, 1.984 m in diameter and was powered by two solar panels.

The satellite observed perpendicular to its orbital plane, meaning there were no Earth occultations, allowing up to 150 days of continuous observation. These observation sessions, called "Long Runs", allowed detection of smaller and long-period planets. During the remaining 30 days between the two main observation periods, CoRoT observed other patches of sky for a few weeks long "Short Runs", in order to analyze a larger number of stars for the asteroseismic program. After the loss of half the field of view due to failure of Data Processing Unit No. 1 in March 2009, the observation strategy changed to 3 months observing runs, in order to optimize the number of observed stars and detection efficiency.

The spacecraft monitored the brightness of stars over time, searching for the slight dimming that happens in regular intervals when planets transit their host star. In every field, CoRoT recorded the brightness of thousands stars in the V-magnitude range from 11 to 16 for the extrasolar planet study. In fact, stellar targets brighter than 11 saturated the exoplanets CCD detectors, yielding inaccurate data, whilst stars dimmer than 16 don't deliver enough photons to allow planetary detections. CoRoT was sensitive enough to detect rocky planets with a radius two times larger than Earth, orbiting stars brighter than 14; it is also expected to discover new gas giants in the whole magnitude range.

CoRoT also studied asteroseismology. It can detect luminosity variations associated with acoustic pulsations of stars. This phenomenon allows calculation of a star's precise mass, age and chemical composition and will aid in comparisons between the sun and other stars. For this program, in each field of view there was be one main target star for asteroseismology as well as up to nine other targets. The number of observed targets have dropped to half after the loss of Data Processing Unit No. 1.

The mission began on 27 December 2006 when a Russian Soyuz 2-1b rocket lifted the satellite into a circular polar orbit with an altitude of 827 km. The first scientific observation campaign started on 3 February 2007.

Until March 2013, the mission's cost will amount to, of which 75% is paid by the French space agency CNES and 25% is contributed by Austria, Belgium, Germany, Spain, Brazil and the European Space Agency ESA.

The primary contractor for the construction of the CoRoT vehicle was CNES, to which individual components were delivered for vehicle assembly. The COROT equipment bay, which houses the data acquisition and pre-processing electronics, was constructed by the LESIA Laboratory at the Paris Observatory and took 60 to complete. The design and building of the instruments were done by the Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA) de l'Observatoire de Paris, the Laboratoire d'Astrophysique de Marseille, the Institut d'Astrophysique Spatiale (IAS) from Orsay, the Centre spatial de Liège (CSL) in Belgium, the IWF in Austria, the DLR (Berlin) in Germany and the ESA Research and Science Support Department. The 30 cm afocal telescope Corotel has been realized by Alcatel Alenia Space in the Centre spatial de Cannes Mandelieu.

Before the beginning of the mission, the team stated with caution that CoRoT would only be able to detect planets few times larger than Earth or greater, and that it was not specifically designed to detect habitable planets. According to the press release announcing the first results, CoRoT's instruments are performing with higher precision than had been predicted, and may be able to find planets down to the size of Earth with short orbits around small stars.
The transit method requires the detection of at least two transits, hence the planets detected will mostly have an orbital period under 75-day. Candidates that show only one transit have been found, but uncertainty remains about their exact orbital period.

CoRoT should be assumed to detect a small percentage of planets within the observed star fields, due to the low percentage of exoplanets that would transit from the angle of observation of the Solar System. The chances of seeing a planet transiting its host star is inversely proportional to the diameter of the planet's orbit, thus close in planets detections will outnumber outer planets ones. The transit method is also biased toward large planets, since their very depth transits are more easily detected than the shallows eclipses induced by terrestrial planets.

On 8 March 2009 the satellite suffered a loss of communication with Data Processing Unit No. 1, processing data from one of the two photo-detector chains on the spacecraft. Science operations resumed early April with Data Processing Unit No. 1 offline while Data Processing Unit No. 2 operating normally. The loss of photo-detector chain number 1 results in the loss of one CCD dedicated to asteroseismology and one CCD dedicated to planet detection. The field of view of the satellite is thus reduced by 50%, but without any degradation of the quality of the observations. The loss of channel 1 appears to be permanent.

Interesting transiting planets could be further followed-up with the infrared Spitzer Space Telescope, to give an independent confirmation at a different wavelength and possibly detect reflected light from the planet or the atmospheric compositions. COROT-7b and COROT-9b have already been observed by Spitzer.

Papers presenting the results of follow-up operations of planetary candidates in the IRa01, LRc01, LRa01, SRc01 fields have been published. Sometimes the faintness of the target star or its characteristics, such as a high rotational velocity or strong stellar activity, do not allow to determine unambiguously the nature or the mass of the planetary candidate.

Discoveries were numerous. Let us cite the first detection of solar-like oscillations in stars other than the Sun, the first detection of non-radial oscillations in red giant stars, the detection of solar-like oscillations in massive stars, the discovery of hundreds of frequencies in δ Scuti stars, the spectacular time evolution of the frequency spectrum of a Be (emission lines B) star during an outburst, the first detection of a deviation from a constant period spacing in gravity modes in an SPB (Slowly Pulsating B) star. Interpreting those results opened new horizons in our vision of stars and galaxies. In October 2009 the CoRoT mission was the subject of a special issue of "Astronomy and Astrophysics", dedicated to the early results of the probe. Below are some examples of breakthrough contributions to stellar astrophysics, based on CoRoT's data:

Another unexpected CoRoT discovery was the presence of solar-like oscillations in massive stars. The small convective shell related to the opacity peak resulting from the ionization of iron group elements at about 200 000 K (iron opacity peak) could indeed be responsible for the stochastic excitation of acoustic modes like those observed in our Sun.

During a 23-day observing run in March 2008, CoRoT observed 636 members of the young open cluster NGC 2264. The so-called "Christmas tree cluster", is located in the constellation Monoceros relatively close to us at a distance of about 1800 light years. Its age is estimated to be between 3 and 8 million years. At such a young age, the cluster is an ideal target to investigate many different scientific questions connected to the formation of stars and early stellar evolution. The CoRoT data of stars in NGC 2264 allow us to study the interaction of recently formed stars with their surrounding matter, the rotation and activity of cluster members as well as their distribution, the interiors of young stars by using asteroseismology, and planetary and stellar eclipses.

The CoRoT observations led to the discovery of about a dozen pulsating pre-main sequence (PMS) δ Scuti stars and the confirmation of the existence of γ Doradus pulsations in PMS stars. Also the presence of hybrid δ Scuti/γ Doradus pulsations was confirmed in members of NGC 2264. The CoRoT observations included also the well known pre-main sequence pulsators, V 588 Mon and V 589 Mon, which were the first discovered members of this group of stars. The precision attained in the CoRoT light curves also revealed the important role of granulation in pre-main sequence stars.

The investigation of T Tauri stars and their interaction with their circumstellar matter using CoRoT data revealed the existence of a new class, the AA Tauri type objects. Previously to the CoRoT observations, T Tauri stars were known to either show sinusoidal light variations that are caused by spots on the stellar surface, or completely irregular variability that is caused by the gas and dust disks surrounding the young stars. AA Tauri type objects show periodically occurring minima that are different in depth and width, hence are semi-regular variables. With the CoRoT observations this class of objects could be established. Exciting insights into the earliest phases of stellar evolution also come from the comparison of the variability present in the optical light to that in the infrared and the X-ray regime.

CoRoT discovered its first two planets in 2007: the hot Jupiters COROT-1b and COROT-2b. Results on asteroseismology were published in the same year.

In May 2008, two new exoplanets of Jupiter size, COROT-4b and COROT-5b, as well as an unknown massive celestial object, COROT-3b, were announced by ESA.

In February 2009, during the First Corot Symposium, the super-earth COROT-7b was announced, which at the time was the smallest exoplanet to have its diameter confirmed, at 1.58 Earth diameters. The discoveries of a second non-transiting planet in the same system, COROT-7c, and of a new Hot Jupiter, COROT-6b, were also announced at the Symposium.

In March 2010 COROT-9b was announced. It's a long period planet (95.3 days) in an orbit close to that of Mercury.

In June 2010 the CoRoT team announced six new planets, COROT-8b, COROT-10b, COROT-11b, COROT-12b, COROT-13b, COROT-14b, and a brown dwarf, COROT-15b. All the planets announced are Jupiter sized, except COROT-8b, which appears to be somewhat between Saturn and Neptune. The probe was also able to tentatively detect the reflected light at optical wavelengths of HD46375 b, a non-transiting planet.

In June 2011, during the Second CoRoT Symposium, the probe added ten new objects to the Exoplanet catalogue: COROT-16b, COROT-17b, COROT-18b, COROT-19b, COROT-20b, COROT-21b, COROT-22b, COROT-23b, COROT-24b, COROT-24c.

As of November 2011, around 600 additional candidate exoplanets are being screened for confirmation.

Among the exoplanets CoRoT detected, one can highlight a subset with the most original features :

The following transiting planets have been announced by the mission.

"Light green rows indicate that the planet orbits one of the stars in a binary star system."
The following table illustrates brown dwarf detected by COROT as well as non-transiting planets detected in the follow-up program:
 All Corot planets were detected during long runs "i.e." of at least 70 days. The "detection team " found on average between 200 and 300 cases of periodic events for each run, corresponding to 2–3% of the stars monitored. Of these, only 530 in total were selected as candidate planets (223 in the direction of the galactic anti-center and 307 towards the center ). Only 30 of them were finally found to be true planets, "i.e." about 6%, other cases being eclipsing binaries ( 46%) or unresolved cases (48%).

The CoRoT planets cover the wide range of properties and features found in the disparate family of exoplanets: for instance, the masses of CoRoT planets cover a range of almost four orders of magnitude, as shown on Figure.

Tracing the mass of the planet versus the mass of the star (Figure), one finds that the CoRoT data set, with its lower scatter than other experiments, indicates a clear trend that massive planets tend to orbit massive stars, which is consistent with the most commonly accepted models of planetary formation.