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, a super-Earth uncovered by the CoRoT mission. However, unlike CoRoT-7b, it was not detected by the transit method from the CoRoT satellite, but only by the radial velocity method using HARPS from La Silla Observatory, Chile. 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
Like CoRoT-7b, 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[1] to 13.5 Earth masses,[3] passing through 12.4 Earth masses[4] and 13.1 Earth masses.[5] This mass range encompasses the Super-Earths to Neptunes transition, so the nature of CoRoT-7c, either a rocky planet or an ice giant, remains unclear. However, if the larger mass estimates are correct, CoRoT-7c is probably a hot Uranus-like planet. Chances are high that planet's rotation is tidally locked to the orbital period, with one side of the planet always facing the star CoRoT-7 and the other one in permanent darkness.
A third planet, CoRoT-7d, is present in the system. Strong mutual gravitational forces could be exchanged between these planets, leading to powerful tidal forces.
Doubts about existence
A published study[6] cast doubt on CoRoT-7c's existence, arguing that the combined presence of stellar activity and additional errors on HARPS radial velocity measurements preclude a meaningful search for additional companions besides CoRoT-7b. However, all the other studies seem to confirm the planet's existence: the signal in the HARPS 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 CoRoT-7b. The remarkable stability and precision showed by the HARPS spectrograph[7] also speaks in favour of the detection. The status of CoRoT-7c seems very well confirmed.
References
^ abcdQueloz, D.; Bouchy, F.; Moutou, C.; Hatzes, A.; Hebrard, G.; Alonso, R.; Auvergne, M.; Baglin, A.; Barbieri, M.; Barge, P.; Benz, W.; Bordé, P.; Deeg, H.; Deleuil, M.; Dvorak, R.; Erikson, A.; Ferraz Mello, S.; Fridlund, M.; Gandolfi, D.; Gillon, M.; Guenther, E.; Guillot, T.; Jorda, L.; Hartmann, M.; Lammer, H.; Léger, A.; Llebaria, A.; Lovis, C.; Magain, P.; Mayor, M.; Mazeh, T.; Ollivier, M.; Pätzold, M.; Pepe, F.; Rauer, H.; Rouan, D.; Schneider, J.; Segransan, D.; Udry, S. & Wuchterl, G. (2009). "The CoRoT-7 planetary system: two orbiting Super-Earths"(PDF). Astronomy and Astrophysics. 506 (1): 303–319. Bibcode:2009A&A...506..303Q. doi:10.1051/0004-6361/200913096. Also available from exoplanet.euArchived 2012-01-11 at the Wayback Machine
