Planet or "failed star" ? CoRoT finds a unique object
1er octobre 2008
The CoRoT satellite has discovered a planet-sized object so exotic that astronomers are unsure whether to call it a planet. The object, named CoRoT-Exo-3b, has approximately the same size as Jupiter, but more than 20 times the mass, it is therefore twice as dense as lead. Its mass is bigger than a planet, but smaller than a star. Every 4 days and 6 hours it passes in front of its host star, which is slightly larger than the Sun. The companion was found thanks to its transits, the small dips in the star’s brightness, that Corot detected every time when that object passed in front of its star. Among the network of ground telescopes used for its characterisation, a team from Paris Observatory was responsible of high resolution imagery observations, carried out with Megacam on the Canada-France-Hawaii telescope.
- Figure 1 : Courbe de lumière blanche de l’étoile CoRoT-Exo3, sur laquelle on distingue les transits produits par la planète Exo3b. La courbe a été normalisée par sa propre médiane (Deleuil et al. 2008) Cliquer sur l’image pour l’agrandir
"It was a surprise to find such a companion of this mass so close to its host star", says Dr. Magali Deleuil from the Laboratoire d’Astrophysique de Marseille (LAM), who led the team for this discovery. She adds : "CoRoT-Exo-3b is a unique object, hence its nature is under debate."
After nearly 15 years of intensive searches for close companions with orbital period less than 10 days, astronomers have found many planets with masses up to 12 Jupiter masses. They have also found stars with masses down to 70 Jupiter masses, but nothing in between at so short orbital period. Many had started to think that such objects did not exist. With 20 Jupiter masses CoRoT-Exo-3b opens up the discussion whether to categorize it as a planet or a brown dwarf.
Dr. Hans Deeg, a member of the discovery team from the Instituto de Astrofisica de Canarias (IAC), explains why this new object is such an important find for planet hunters : "It could also be a very low-mass brown dwarf, a "failed star" which never got massive and hot enough to shine like a normal star. There is no clear consensus among scientists where to draw the exact boundary between planets and brown dwarfs. No object has been found before which is so close to this boundary."
Dr. Deleuil points out that "As a planet, CoRoT-Exo-3b would be the most massive and densest found to date - more than twice as dense as lead. Just how such a massive, close companion can form is an open question". "Of course, it could be a rare object which CoRoT found by sheer luck", comments Dr. Francois Bouchy, another member of the discovery team from Institut d’Astrophysique de Paris (IAP), "but it could also be the first member of a new family of very massive planets which form around stars more massive than our Sun. There seems to be an emerging trend : the more massive the star the more massive the planet."
This discovery was supported by ground-based observations using a network of facilities operated by different institutes and in different countries : the telescope of Observatoire de Haute Provence (France), the European Southern Observatory telescopes at Paranal and La Silla (Chili), the Thuringia State Observatory in Tautenburg (Germany), the Canada-France-Hawaii Telescope on Mauna Kea, and a series of 1-m class telescopes : the swiss Euler Telescope at La Silla (Chile), the WISE Observatory (Israel), the European Space Agency telescope on Mt. Teide, (Tenerife) and the 80cm telescope of the Astrophysical Institute of the Canary Islands. The team from Paris Observatory was responsible of high resolution imagery, that were carried out with the instrument Megacam on the Canada-France-Hawaii telescope.
See also the Press Release from INSU/CNRS
Learn more about the CoRoT mission, instigated by researchers from Paris Observatory, financed essentially by France, with the collaboration of Autria, Germany, Belgium, Brazil, Spain, the European Space Agency (ESA), and realized by the CNES. Previous scientific news on CoRoT : Last news from the CoRoT satellite (July 2008) CoRoT discovers 5 exoplanets (May 2008) CoRoT : 300 days in orbit (Novembre 2007) CoRoT : discovery of an exoplanet and first stellar oscillations (May 2007) CoRoT first image (January 2007)
References
Transiting exoplanets from the CoRoT space mission : VI. CoRoT-Exo-3b : the first secure inhabitant of the brown-dwarf desert M. Deleuil, H. Deeg, R. Alonso, F. Bouchy, D. Rouan et al. Astronomy & Astrophysics, in press
Contacts
Daniel Rouan (Observatoire de Paris, LESIA, et CNRS)
Annie Baglin (Observatoire de Paris, LESIA, et CNRS)
Dernière modification le 4 mars 2013