CoRoT (French: Convection, Rotation et Transits planétaires; English: Convection, Rotation and planetary Transits) was a space telescope 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. 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 was the first spacecraft dedicated to the detection of transiting extrasolar planets, opening the way for more advanced probes such as Kepler and TESS. 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 had been retired and would be decommissioned; lowered in orbit to allow it to burn up in the atmosphere.

Overview

Spacecraft design

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 27 cm 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 2,048 by 2,048 pixel array. Each pixel is 13.5 μm × 13.5 μm in size which corresponds to an angular pixel size of 2.32 arcsec. The CCDs are cooled to -40 C. 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.

Mission design

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 had to not be too sparse – fewer targets observed – or too crowded – too many stars overlapping. Several fields were observed during the mission: 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 do not 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 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. The mission's cost amounted to €170 million, of which 75% was paid by the French space agency CNES and 25% was contributed by Austria, Belgium, Germany, Spain, Brazil and the European Space Agency (ESA).

Development

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 person-years 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.

Potential

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.

Failure of Data Processing Unit No. 1

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.

Follow-up program

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. In April 2019, a summary of the exoplanet search results have been published, with 37 planets and brown dwarves confirmed, and a further one hundred planet candidates still to be verified. 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

Asteroseismology and stellar physics

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 on 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 seismo 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 seismo 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, including 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 humanity's 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:

Extension of the chemically mixed zone in main sequence stars

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.

Structure of the superficial stellar layers

Red giants and chemical evolution of this galaxy

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 100 106 K, helium starts burning in the core. For stellar masses smaller than about 2 Mʘ, 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 νmax 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 stars

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 the Sun.

The open cluster NGC 2264

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.

Binary systems

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.

Exoplanets

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 2T and 3T 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 a3 = T2 Mstar, 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 Astronomic 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 (34 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.

Timeline of planetary discoveries

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.

Main results

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

List of exoplanets discovered

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.

Other discoveries

The following table illustrates brown dwarfs detected by CoRoT as well as non-transiting planets detected in the follow-up program:

Global properties of the exoplanets discovered by CoRoT

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 detection capabilities of Corot are illustrated by the figure D showing the depth of the transits measured for all candidates, depending on the period and the brightness of the star: there is indeed a better ability to detect small planets (up to 1.5 R Earth ) for short periods (less than 5 days) and bright stars. 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.