COROT Finds Exoplanet Diversity

The CoRoT spacecraft. Credit: CNES/D.Ducros

Ten new exoplanets have been discovered by the European satellite, CoRoT. Confirmed via meticulous, ground-based observations, these exoplanets exhibit a wide variety of masses, densities, orbital parameters and other properties, highlighting the broad diversity of planets around stars other than our sun.

The inventory includes seven hot Jupiters, a planet smaller than Saturn and a system of two Neptune-like objects orbiting the same star. The results were announced June 14, 2011, at the Second CoRoT Symposium held in Marseille, France.

CoRoT is the first space mission dedicated to the search for planets outside our solar system. In more than 4 years of operations 26 new exoplanets have been discovered with CoRoT, bringing the total number of exoplanets known thus far to 565.

When the hunt for planets around stars other than the Sun began, over 15 years ago, achieving a detection was the primary goal of the field. After almost two decades of research, great technological progress, and the discovery of several hundred exoplanets, the focus has now shifted towards a more analytical approach. Astronomers exploit the joint power of dedicated space-based facilities, such as CoRoT, and high-quality data from the ground in order to pin down the characteristics of a large number of planets.

With these data at hand, it is possible to tackle fundamental questions concerning how exoplanets form and what kind of objects emerge from the various formation scenarios. The new results highlight once again the diversity of the properties observed within the ‘zoo’ of exoplanets.

The CoRoT spacecraft has discovered many extrasolar planets. Above is an artist’s impression of the planet, CoRoT-7b, which the telescope identified in 2009. Credit: ESO/L. Calcada

“Ever since the early days of exoplanet astronomy, we’ve been amazed by the variety of planets that have been discovered: gaseous giants larger than Jupiter and smaller, rocky bodies, down to masses comparable to the Earth’s,” notes Malcolm Fridlund, ESA’s project scientist for CoRoT.

The configurations of the systems are also highly diverse, with a wide range of orbital periods, and about 70 systems in which multiple planets have been detected. “The new set of ten planets that we announce today are no exception, exhibiting as they do a rich list of very interesting properties,” he adds.

Of the most recent additions to the CoRoT family, seven are so-called ‘hot Jupiters’, one is smaller than Saturn (CoRoT-22b) and the other two (CoRot-24b and CoRot-24c), with masses similar to that of Neptune, have been found orbiting the same star. The densities of these planets, which are all gaseous, span a wide range, from values similar to that of Saturn, the least dense planet in the Solar System, to higher values comparable to the density of Mars.

The host stars also exhibit rather mixed properties, ranging from a ten thousand million year old star — twice as old as the Sun — in the case of CoRoT-17b, to a rather young (about 600 million years) counterpart, in the case of CoRoT-18b. Observing planetary systems with such different ages is particularly useful when testing different scenarios of planet formation and evolution. Two of the planets (CoRoT-16b and CoRoT-20b) lie on highly elongated orbits, and explaining their survival on such orbits represents a challenge from the dynamical point of view.

CoRoT is the first space mission dedicated to the search for planets beyond the Solar System. Credit: CNES/D.Ducros

The double system of Neptune-like bodies is rather peculiar, and it will be monitored in the future to determine if it harbors other planets as well.

Since its launch in 2006, CoRoT has detected several hundred candidate planet-hosting stars. Each of them has to undergo a scrupulous validating procedure, in order to assess whether or not the observations truly represent the detection of a planet. This relies on follow-up observations conducted with an extensive network of ground-based telescopes. Astronomers from the CoRoT team, including a number of ESA researchers, collect a wealth of photometric and spectroscopic data in order to confirm that the detections are actually due to a planet and, in that case, to measure the parameters of the systems.

“Although the study of exoplanets is relatively young, we have already reached a stage where we can characterize the details of worlds orbiting other stars, and CoRoT is making a crucial contribution to this field,” comments Fridlund. “With hundreds of systems observed to date, we no longer have to worry about ‘taming the beasts’ and we can dedicate our efforts to the ‘zoology’ of exoplanets, which is enormously enhancing our knowledge about planetary systems,” he concludes.