CoRoT discovers 10 new extra-solar planets
14 June 2011 -- The satellite CoRoT has identified through transit 10 new exoplanets, that were confirmed with follow-up observations from the ground. Seven are hot Jupiters, with sometimes unusual properties, and three have smaller masses: one is slightly smaller than Saturn, and two are Neptune-sized planets orbiting the same star. These discoveries were announced at the second CoRoT Symposium, held this week in Marseille.
Astronomers worldwide have detected more than 550 extrasolar planets -- planets around other stars than our Sun -- since the hunt began in earnest around 20 years ago. They are more diverse than anyone imagined. While some need years to circle their star, others do it in less than a day. They come in all sizes from gaseous giants twice as large as Jupiter to small planets comparable to Earth, and everything in between.
The European satellite CoRoT, led by the French space agency CNES (Centre national d'études spatiales) was the first space mission designed to find extrasolar planets. Now entering its fifth year of operations, it has detected hundreds of candidate planets, many of which are the subject of ongoing studies to pin down their true nature, and 15 confirmed planets across the full size range. CoRoT uses the transit method, monitoring tens of thousands of stars simultaneously and detecting tiny, periodic dips in brightness caused by a planet passing in front of its host star. Transits uniquely allow astronomers to measure the radius of the planets and, combined with ground-based observations, to determine its mass.
The 10 new confirmed planets -- whose details are given below -- are CoRoT-16b through to 24b and c. Seven are hot Jupiters some of which are unusually dense and/or on unusually elongated orbits, and one is in orbit around an unusually young star. There is much to be learnt from these systems about the way giant planets form and evolve. The announcement also includes a planet slightly smaller than Saturn, and two Neptune-sized planets orbiting the same star. Only a handful of this kind of planets have yet been characterized in detail, which makes them particularly valuable.
Details of the new planets:
- CoRoT-16b: A puffed-up short-period giant planet, with the radius of Jupiter and half of its mass. It orbits in 5.3 days around a mature Sun-like star with an age of 6 billion years. The orbit of this planet is eccentric which is rare for such an old, close-in planet.
- CoRoT-17b: A massive giant planet around a star with an age of 10 billion years, or twice as old as our Sun. It orbits in 3.7 days, has 2.4 Jupiter masses and a density twice that of Jupiter. Observing such an old planetary system is important for understanding the long term evolution of giant planets.
- CoRoT-18b: The orbit of this Hot Jupiter has a 1.9-day period and is aligned with the equator of its star. This planet has a size 1.4 times that of Jupiter but 3.5 times its mass, so it is denser than Jupiter.
- CoRoT-19b: A planet with the same mass as Jupiter but 1.5 times the size. It has a density much less than that of Saturn, the least dense planet in our solar system.
- CoRoT-20b: A "Hot Jupiter" in an eccentric orbit with a period of 9.2 days. CoRoT-20b is special because it has a very eccentric orbit which may be related to its extremely high density. It has a density twice that of Mars, even though it is a gaseous giant planet.
- CoRoT-21b: A giant gas planet with a size 1.3 times that of Jupiter and 2.5 times the mass. This is one of the faintest CoRoT stars for which the planet mass has been determined. These mass measurements required observations with the Keck 10m telescope in Hawaii.
- CoRoT-22b: This planet has a size of 0.62 radii that of Saturn. The mass of this exoplanet has yet to be determined precisely, but it is certainly less than half that of Saturn.
- CoRoT-23b: A "Hot Jupiter" in a 3.6 day orbit with another unexpected eccentric orbit.
- CoRoT-24b and 24c: A system with two transiting planets of Neptune size in orbits of 5.1 and 11.8 days. The planets have sizes 4.2 and 2.7 Earth radii, respectively.
Figure 1: Corot-23b : curve of the radial velocity, presenting departure from the sinusoid, characteristic of a non-zero excentricity (here e = 0.16).
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Figure 2: Corot-24b-c: transits of CoRoT-24b and CoRoT-24c, the first system with several transiting planets observed by CoRoT.
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The CoRoT Space Mission:
CoRoT is a 27cm space telescope that searches for exoplanets with the so-called transit method. The transit method measures the tiny decrease in brightness when an object passes in front of a star. The CoRoT space mission is led by the French space agency CNES (Centre national d'études spatiales) with support from the European Space Agency (ESA), Austria, Belgium, Germany (DLR), Spain, and Brazil.
Since its launch in December 2006, CoRoT has already found 24 confirmed extrasolar planets. The number of possible extrasolar planets is even larger: CoRoT has identified 401 possible planet candidates that are in the process of being confirmed. In order to determine whether these candidates are actually extrasolar planets, the CoRoT team uses ground-based telescopes worldwide for follow-up observations.
The Ground-based Support Segment:
Data from CoRoT can only determine the radius of the planet. The measurement of the planetary mass requires observations from the ground using the so-called Doppler wobble method. Additional measurements from the ground are also required to exclude other phenomena that may mimic a transit signal. A number of ground-based telescopes support CoRoT observations and contribute to the characterization of planets: the Canada France Hawaii Telescope (INSU-CNRS, CNRC, U. Hawaii), the IAC80 and the ESA-OGS of Teide Observatory, Spain, the 1,2m telescope at Observatoire Haute Provence, France, the Swiss Euler 1.2m telescope in Chile, the 0.46 and 1m Wise Observatory, Israel, telescopes of the Thuringia State Observatory, Germany, the BEST and BEST II telescopes of Deutsches Zentrum für Luft- und Raumfahrt (DLR), the Sandiford Spectrograph on the 2.1m Otto Struve Telescope at McDonald Observatory (Texas, USA), the FIES spectrograph on the 2.56m Nordic Optical Telescope at La Palma (Spain), 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 with UVES, CRIRES and NACO, the HIRES spectrograph (under NASA Keck time) on the 10m KECK telescope at Hawaii, USA and the SOPHIE spectrograph, on the 1.93m telescope at Haute Provence Observatory in France.
Daniel Rouan (Observatoire de Paris-LESIA, CNRS, UPMC, UDD)
Benjamin Samuel (Observatoire de Paris-LESIA, CNRS, UPMC, UDD)
Jean Schneider (Observatoire de Paris-LUTH, CNRS)