Structure of Super-Earths- Ocean or Rocky?
Abstract
In the last two years, three planets with masses below 10 earth-masses (ie. super-Earths) have been discovered. We expect many more to follow with space missions like CoRoT - already in space - and Kepler, launching next year. These are exciting new objects. Among them we might find Earth analogs. Owing to their small masses it is unlikely that super-Earths have a gas envelope and therefore are either terrestrial or ocean-like (with a substantial amount of H2O - mostly in the solid phase due to high pressures). We have detailed structure models for these planets that allow us to predict their bulk composition and structure properties from planetary mass and radius measurements. We find that there is a terrestrial threshold radius (TTR) above which a planet is necessarily ocean-like, implying wet conditions during formation. The precision at which super-Earths will be detected ( 4% in radius by Kepler and 10% in mass by HARPS-NEF) is sufficient to show if the planet is ocean-like. Moreover, information of dynamics of the system might be extracted by knowing the planet's composition and heliocentric distance. For example, if the radius of GJ 876d was larger than 12000km, it would mean it has a large amount of H2O that had to be acquired beyond the snow line. At an orbital distance of 0.02AU, this suggests evidence for migration of this super-Earth in the presence of the other two giant planets in the system.
- Publication:
-
American Astronomical Society Meeting Abstracts #210
- Pub Date:
- May 2007
- Bibcode:
- 2007AAS...21011006V