On the possible properties of small and cold extrasolar planets: Is OGLE 2005-BLG-390LB entirely frozen?

Research areas:
Year:
2006
Authors:
  • David Ehrenreich
  • Alain Lecavelier des Etangs
  • Jean-Philippe Beaulieu
  • Olivier Grasset
Journal:
ASTROPHYSICAL JOURNAL
Volume:
651
Number:
1, 1
Pages:
535-543
Month:
NOV 1
ISSN:
0004-637X
BibTex:
Abstract:
Extrasolar planets as light as a few Earth masses are now being
detected. Such planets are likely not gas or ice giants. Here, we
present a study on the possible properties of the small and cold
extrasolar planets, applied to the case of the recently discovered
planet OGLE 2005- BLG-390Lb. This planet (5.5(-2.7)(+5.5) M(circle
plus)) orbits 2.6(-0.6)(+1.5) AU away from an old M- type star of the
Galactic bulge. The planet should be entirely frozen given the low
surface temperature (35-47 K). However, depending on the rock-to-ice
mass ratio in the planet, the radiogenic heating could be sufficient to
make the existence of liquid water within an icy crust possible. This
possibility is estimated as a function of the planetary mass and the
illumination received from the parent star, both being strongly related
by the observational constraints. The results are presented for
water-poor and water-rich planets. We find that no oceans can be present
in any cases at 9-10 Gyr, a typical age for a star of the bulge.
However, we find that in the past, when the planet was less than or
similar to 5 Gyr old, liquid water was likely present below an icy
surface. Nevertheless, the planet is now likely to be entirely frozen.