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Six new planets discovered by CoRoT telescope

14 June 2010

The CoRoT team have announced the discovery of six diverse new planets, from ‘shrunken-Saturns’ to ‘bloated hot Jupiters’ as well a very rare brown dwarf with 60 times the mass of Jupiter.

CoRoT, a space telescope operated by the French space agency CNES, discovers exoplanets when they pass in front of their stars - the so-called ‘transit method’.

Once CoRoT detects a transit, additional observations are made from the ground, using a number of telescopes all over the world. Although astronomers cannot see the planets directly, they use the space- and ground-based data to measure the sizes, masses, and orbits of these new planets precisely. This is why, among all known exoplanets, those with transits yield the most complete information about planet formation and evolution.

‘Every discovery of an extrasolar planetary system is a new piece in the puzzle of how these systems do form and evolve. The more systems we uncover, the better we can hope to understand the processes at play,’ said Magali Deleuil, researcher at the Laboratoire d'Astrophysique de Marseille (LAM) and head of the CoRoT exoplanet program.

‘Each of these planets is interesting in its own right, but what is really fascinating is how diverse they are. Planets are intrinsically complex objects, and we have much to learn about them yet,’ said co-investigator Dr Suzanne Aigrain from Oxford University’s Department of Physics.

The six new planets are:

CoRoT-8b: the smallest in this batch: At about 70% of the size and mass of Saturn, CoRoT-8b is moderately small among the previously known transiting exoplanets. Its internal structure should be similar to that of ice giants, like Uranus and Neptune, in the Solar System. It is the smallest planet discovered by the CoRoT team so far after CoRoT-7b, the first transiting Super-Earth.

CoRoT-10b: the eccentric giant: The orbit of CoRoT-10b is so elongated that the planet passes both very close to and very far away from its star. The amount of radiation it receives from the star varies tenfold in intensity, and scientists estimate that its surface temperature may increase from 250 to 600°C, all in the space of 13 Earth-days (the length of the year on CoRoT-10b).

CoRoT-11b: the planet whose star does the twist: CoRoT-11, the host star of CoRoT-11b, rotates around its axis in 40 hours. For comparison, the Sun’s rotation period is 26 days. It is particularly difficult to confirm planets around rapidly rotating stars, so this detection is a significant achievement for the CoRoT team.

CoRoT-12b, 13b and 14b: a trio of giants: These three planets all orbit close to their host star but have very different properties. Although CoRoT-13b is smaller than Jupiter, it is twice as dense. This suggests the presence of a massive rocky core inside the planet. With a radius 50% large than Jupiter’s (or 16 times larger than the Earth’s), CoRoT-12b belongs to the family of `bloated hot Jupiters’, whose anomalously large sizes are due to the intense stellar radiation they receive. On the other hand, CoRoT-14b, which is even closer to its parent star, has a size similar to Jupiter’s. It is also massive, 7.5 times the mass of Jupiter, which may explain why it is less puffed up. Such very massive and very hot planets are rare, CoRoT-14b is only the second one discovered so far.

CoRoT-15b: the brown dwarf: CoRoT-15b’s mass is about 60 times that of Jupiter. This makes it incredibly dense, about 40 times more so than Jupiter. For that reason, it is classified as a brown dwarf, intermediate in nature between planets and stars. Brown dwarfs are much rarer than planets, which makes this discovery all the more exciting.

For more information contact Dr Suzanne Aigrain (UK co-author) of Oxford University’s Department of Physics on mobile: +44 (0)7549 939899 or email: Suzanne.Aigrain@astro.ox.ac.uk

Illustrations related to the research are available from Dr Aigrain on request.

Alternatively contact the University of Oxford Press Office on +44 (0)1865 283877 [weekend: 07738 135619] or email press.office@admin.ox.ac.uk

Notes for editors

Dr Suzanne Aigrain leads a team of UK researchers at the Universities of Oxford, Exeter and St Andrews who participate in the CoRoT exoplanet program. Their research is supported by the Science and Technology Facilities Research Council.
The CoRoT (Convection, Rotation and Transits) space telescope was constructed by the French space agency CNES, with contributions from Austria, Germany, Spain, Belgium, Brazil and the European Space Agency (ESA). It was specifically designed to detect transiting exoplanets and study the interior structure of stars using seismology. CoRoT science operations started in early 2007 and are expected to continue until end 2012.
CoRoT detects planets by searching for transits, the minute periodic dimmings of a star, which occur when a planet in orbit around them crosses the stellar disk. This is a complex and time-consuming endeavour, which requires follow-up observations from the ground, but it has the unique advantage of yielding both the size and the mass of the planet, and thus its mean density. This gives a first order estimate of the bulk composition of the planet (is it a gaseous giant like Jupiter, or a terrestrial planet like Earth, or something in between?). Together with the orbital characteristics, which can be particularly well determined for transiting planets, these parameters are key to understanding how different kinds of planets form and evolve. In the last fifteen years, astronomers have discovered over 450 exoplanets, of which only 82 transit across their host star. 15 of those were first spotted by CoRoT.
A meticulous analysis: Since February 2007, the CoRoT space telescope observes about 80,000 stars per year. The brightness of each star as a function of time, or its ‘light curve’ in astronomical jargon, is recorded for 20 to 150 days. An international team of scientists from 9 European institutions searches these light curves for periodic micro-eclipses (or transits) which may be cause by the passage of planets in front of their stars: ‘We have chosen to work in parallel, analyzing the full data set independently. By using different methods at the same time, we increase the number of discoveries,’ says Pascal Bordé of the Institut d’Astrophysique Spatiale (IAS) in Orsay. Every year, the team identifies about a thousand light curves featuring transit-like events, of which about a hundred fulfil all the conditions for being good planetary candidates.
Key support from ground-based telescopes: Many things, in particular combinations of two or more stars, can mimic the transit of a planet. The CoRoT team can only claim a detection of a planet when all other scenarios have been rejected: ‘People usually don't realize that, between the detection of a transit by CoRoT and the official announcement of a new planet, there is an intense campaign of follow-up observations that may take as long as two full years!’ explains Claire Moutou, also from LAM, who is in charge of coordinating the follow-up program. CoRoT planet hunters must thus scrutinize from the ground about a hundred potential planet-bearing stars per year. About fifteen telescopes all over the world are used for this task. First, the team must check which star is being eclipsed, as more than one star usually contributes to a single brightness measurement by CoRoT, by re-observing the transit from the ground with larger telescope than CoRoT’s own. Then, they must demonstrate that the transiting body is a genuine planet and not a star by measuring its mass. Finally, they must determine precisely what kind of star the planet is orbiting, which is done by obtaining a high-quality spectrum of the star.
List of telescopes which support CoRoT observations: The IAC-80 (Teide Observatory), the Canada France Hawaii Telescope (Hawaii), the Isaac Newton Telescope (Roque de los Muchachos Observatory), Wise Observatory (Israel), the 2-m telescope of Tautenburg Observatory (Germany), the Swiss Euler 1.2m telescope in Chile, the Faulkes North Telescope of the Las Cumbres Observatory Global Telescope Network (Hawaii), the HARPS spectrograph on the 3.6 m telescope (ESO/Chile), the ESO's 8.2-m Very Large Telescopes at Paranal Observatory in Chile, the HIRES spectrograph on the 10m KECK telescope at Hawaii (USA) and the SOPHIE spectrograph, on the 1.93m telescope at Haute Provence Observatory in France.