XX. CoRoT-20b: A very high density, high eccentricity transiting giant planet

TL;DR

CoRoT-20b is a highly dense, high-eccentricity giant planet with unique structural characteristics and tidal evolution, challenging existing planet formation and evolution models.

Contribution

This paper reports the discovery and detailed characterization of CoRoT-20b, highlighting its extreme density, high eccentricity, and implications for planetary formation and tidal evolution theories.

Findings

CoRoT-20b has a mass of 4.24 MJ and a radius of 0.84 RJ.

It has an exceptionally high density of 8.87 g/cm^3.

The planet's orbit is highly eccentric with e=0.56.

Abstract

We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/- 0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most compact planets known so far. Evolution models for the planet suggest a mass of heavy elements of the order of 800 ME if embedded in a central core, requiring a revision either of the planet formation models or of planet evolution and structure models. We note however that smaller amounts of heavy elements are expected from more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56. The star's projected rotational velocity is vsini = 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving towards a triple synchronous state with equality of the orbital, planetary and stellar spin periods.