Free access article

A&A 463, 359-367 (2007)
DOI: 10.1051/0004-6361:20066582

Co-orbital terrestrial planets in exoplanetary systems: a formation scenario

C. Beaugé¹, Zs. Sándor², B. Érdi², and Á. Süli<sup>2

1</sup>  Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, (X5000BGR) Córdoba, Argentina
    e-mail: beauge@oac.uncor.edu
²  Department of Astronomy, Loránd Eötvös University, Pázmány Péter sétány. 1/A, 1117 Budapest, Hungary
    e-mail: [Zs.Sandor;B.Erdi;A.Suli]@astro.elte.hu

(Received 17 October 2006 / Accepted 11 November 2006)

Abstract
Aims.We study the formation of a hypothetical terrestrial-type body in the equilateral Lagrange points of a giant extrasolar planet. Starting from a swarm of planetesimals in stable tadpole orbits, we simulate its dynamical and collisional evolution under a wide range of different initial conditions and masses for both the Trojan population and its planetary companion. We also analyze the effects of gas drag from the interaction of the planetesimals with the nebular disk.
Methods.The formation process is simulated with an N-body code that considers full gravitational interactions between the planetesimals and the giant planet. Gas interaction is modeled with Stokes and Epstein drags, where the drag coefficients are chosen following the results of full hydrodynamic simulations performed with the 2D public hydro-code FARGO.
Results.In both gas-free and gas-rich scenarios, we have been able to obtain a single final terrestrial-type body in a stable tadpole orbit around one of the triangular Lagrange points of the system. However, due to gravitational instabilities within the swarm, the accretional process is not very efficient and the mass of the final planet never seems to exceed ~0.6 Earth masses, even when the total mass of the swarm is five times this value. Finally, we also included an orbital decay of the giant planet due to a type II migration. Although the accretional process shows evidence of a lower efficiency, a small terrestrial planet is still able to form, and follows the giant planet towards the habitable zone of the hosting star.

Key words: celestial mechanics -- planets and satellites: formation -- methods: N-body simulations

© ESO 2007

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