Exploring the Diversity of Exoplanets in the Mass-Density Diagram

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The mass-density diagram is an important diagnostic for understanding the large diversity in bulk densities that exoplanets exhibit. In this diagram low-mass planets with masses below ~0.3 MJup show a large scatter in density. For example, super-Earths with masses ~10 MEarth can have a bulk density consistent with a rocky planet (density = 5-8 gm/cm3) or a Neptune-like structure (density ~ 2 gm/cm3). Understanding this diversity may yield clues as to the planet formation. On the other hand, giant planets and brown dwarfs in the mass range 0.3 - 62 MJup show a tight linear relationship in the mass-density diagram with no distinguishing features between the two classes of objects. The mass-density diagram can thus provide clues as to the nature of giant planets and brown dwarfs orbiting stars. Are these really different objects?The light curves of transiting planets obtained from space-based missions like CoRoT and Kepler provide us with the best possible measurements of the planetary radius. However, CoRoT and Kepler targeted relatively faint stars. The determination of the planetary mass via Doppler measurements from the ground was thus difficult. The re-vamped Kepler mission, K2, is observing stars that are 3 magnitudes brighter than Kepler and CoRoT targets. By the end of our proposed project K2 will have obtained precise light curves for almost 300,000 stars. Light curves from TESS shall be included in this project after its successful launch in 2017. The discoveries from K2 and eventually TESS will greatly increase the number of extrasolar planets for which we have accurate measurements of the mass, radius, and bulk density.For this project we have assembled a team from three institutes to exploit the light curves from the K2 and eventually TESS missions. Our team builds on its vast experience as members of the CoRoT Exoplanet Science Team. We have experts in the processing of raw light curves from space instruments, the detections in the light curves, and the modeling of the transit light curves needed to obtain the planetary radius. We also have experts on stellar spectroscopy which will determine the properties of the host stars. We expect this project to yield manyl dozen transiting extrasolar planets with accurate bulk densities throughout the mass-density diagram. This will help us understand the diversity in bulk densities for low-mass planets and the nature of giant planets/brown dwarfs.