ABSTRACT. Recent observation of the microlensing technique reveals two giant planets at 2.3 AU and 4.6 AU around the star OGLE-06-109L. The eccentricity of the outer planet (e_c ) is estimated to be 0.11^+0.17 _–0.04, comparable to that of Saturn (0.01-0.09). The similarities between the OGLE-06-109L system and the solar system indicate that they may have passed through similar histories during their formation stage. In this paper, we investigate the dynamics and formation of the orbital architecture in the OGLE-06-109L system. For the present two planets with their nominal locations, the secular motions are stable as long as their eccentricities (e_b , e_c ) fulfill e ² _b + e ² _c ≤ 0.3². Earth-size bodies might be formed and are stable in the habitable zone (0.25-0.36 AU) of the system. Three possible scenarios may be accounted for the formation of e_b and e_c : (1) convergent migration of two planets and the 3:1 mean motion resonance (MMR) trapping; (2) planetary scattering; and (3) divergent migration and the 3:1 MMR crossing. As we showed that the probability for the two giant planets in 3:1 MMR is low (~3%), scenario (1) is less likely. According to models (2) and (3), the final eccentricity of inner planet (e_b ) may oscillate between [0-0.06], comparable to that of Jupiter (0.03-0.06). An inspection of e_b , e_c 's secular motion may be helpful to understand which model is really responsible for the eccentricity formation.

Key words: planetary systems: formation; solar system: formation; stars: individual (OGLE-06-109L)

Print publication: Issue 1 (2009 November 20)
Received 2009 June 4, accepted for publication 2009 October 13
Published 2009 November 5