CoRoT-7c is an

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

which orbits the G-type main sequence star

CoRoT-7 CoRoT-7 (TYC 4799-1733-1) is a binary star system. The primary, CoRoT-7A is a G-type main sequence star, slightly smaller, cooler, and younger than the Sun. It has an apparent magnitude of 11.67, fainter than Proxima Centauri (mag. 11 ...

, located approximately 489 light years away in the constellation

Monoceros Monoceros (Greek: Μονόκερως, "unicorn") is a faint constellation on the celestial equator. Its definition is attributed to the 17th-century Dutch cartographer Petrus Plancius. It is bordered by Orion to the west, Gemini to the north, ...

. It's either a

super-Earth A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to ...

or a Neptune-like planet, orbiting at 0.046 AU from the star, taking 3.7 days or 89 hours to make one round trip around the star.

Discovery

The discovery of the planet was announced in February 2009, during the First Corot Symposium. It was discovered during the follow-up started in order to confirm the existence of

CoRoT-7b CoRoT-7b (previously named CoRoT-Exo-7b) is an exoplanet orbiting the star CoRoT-7 in the constellation of Monoceros (constellation), Monoceros, from Earth. It was first detected Methods of detecting extrasolar planets#Transit photometry, photome ...

, a super-Earth uncovered by the

CoRoT CoRoT (French: ; 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 th ...

mission. However, unlike

, it was not detected by the

transit method 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 o ...

from the

satellite, but only by the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

using

HARPS The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision echelle planet-finding spectrograph installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. ...

from

La Silla Observatory La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory (ESO). Several other telescopes are located at the site and are partly maintained by ESO. The observatory is ...

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. A posteriori search of transits of CoRoT-7c in the lightcurve of the star CoRoT-7 yielded a negative result, confirming the planet is not transiting. As a consequence no radius measurement is available, and no density and structure models of the planet can be established.

Characteristics

, the mass of CoRoT-7c is weakly constrained, since the radial velocity data is noisy due to the presence of stellar activity. Published mass measurements range from 8.4 Earth masses to 13.5 Earth masses, passing through 12.4 Earth masses and 13.1 Earth masses. This mass range encompasses the Super-Earths to Neptunes transition, so the nature of CoRoT-7c, either a

rocky planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, ...

or an

ice giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune. In astrophysics and planetary scienc ...

, remains unclear. However, if the larger mass estimates are correct, CoRoT-7c is probably a hot

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...

-like planet. Chances are high that planet's rotation is

tidally locked Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally locked bo ...

to the orbital period, with one side of the planet always facing the star

and the other one in permanent darkness. A possible third planet, CoRoT-7d, may be present in the system, but pending further observations its status remains unconfirmed. If this planet is confirmed, strong mutual

gravitational force In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong ...

s could be exchanged between these planets, leading to powerful

tidal forces The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...

Doubts about existence

A published study cast doubt on CoRoT-7c's existence, arguing that the combined presence of stellar activity and additional errors on

radial velocity measurements preclude a meaningful search for additional companions besides

. However, all the other studies seem to confirm the planet's existence: the signal in the

data of CoRoT-7c is detected in analysis of different type, does not seem to be correlated with stellar activity and is stronger than the signal associated with the confirmed

. The remarkable stability and precision showed by the

spectrograph also speaks in favour of the detection. The status of CoRoT-7c seems very well confirmed.

References

{{DEFAULTSORT:Corot-7c Exoplanets discovered in 2009 Monoceros (constellation) Exoplanets detected by radial velocity