Prospects for the habitability of OGLE-2006-BLG-109L

TL;DR

This paper explores the potential habitability of the OGLE-2006-BLG-109L system, showing that additional inner planets could stabilize orbits and make it more similar to our Solar system.

Contribution

It demonstrates that adding an inner planet could enhance habitability prospects by reducing orbital eccentricities caused by the two giant planets.

Findings

Resonant excitation of eccentricities by giant planets

Inner planet of >0.3 Earth masses can stabilize orbits

System could resemble our Solar system with additional planets

Abstract

The extrasolar system OGLE-2006-BLG-109L is the first multiple-planet system to be discovered by gravitational microlensing (Gaudi et al., 2008); the two large planets that have been detected have mass ratios, semimajor axis ratios, and equilibrium temperatures that are similar to those of Jupiter and Saturn; the mass of the host star is only 0.5 M_sun, and the system is more compact than our own Solar system. We find that in the habitable zone of the host star, the two detected planets resonantly excite large orbital eccentricities on a putative earth-mass planet, driving such a planet out of the habitable zone. We show that an additional inner planet of ~>0.3M_earth at <~0.1 AU would suppress the eccentricity perturbation and greatly improve the prospects for habitability of the system. Thus, the planetary architecture of a potentially habitable OGLE-2006-BLG-109L planetary system -- with two ``terrestrial'' planets and two jovian planets -- could bear very close resemblance to our own Solar system.