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P. Thebault (DESPA, Observatoire de Paris), F. Marzari (Universita di Padova), H. Scholl (Observatoire de la Cote d'Azur)
The 47 UMa and Epsilon Eridani extrasolar planetary systems are among those that resemble the most our own solar system, with moderately massive planets (2.4 Mjup and 0.86 minimum mass) on relatively distant orbits (at 2.09 and 3.3 A.U.). It is thus natural to ask whether these systems can harbour terrestrial planets in their inner regions. We numerically investigate how the accretion process of such inner planets might have been affected by the presence of the detected massive external bodies. The crucial point is the timing of the giant planets's formation. We have investigated 2 different scenarios: 1) the perturbing planet was fully formed in the early phases of planetesimal accretion in the inner disk and 2) the giant planet reaches its final mass only later on when lunar-sized embryos already formed in the inner disk. For case 1) we focus on one crucial parameter driving the accretion process: the distribution of encounter velocities in the early inner disk, which is estimated using a deterministic code that takes into account the gravitational pull of external perturbers and the possible effect of gas drag. For case 2) a classical symplectic algorithm is used taking into account the mutual pull of protoplanetary embryos. The Epsilon Eridani system turns out to be very hostile to planetary accretion in the inner disk in the scenario 1) where the planet affects the initial phases of planetesimal accretion. The planet's high eccentricity (0.608) induces too large encounter velocities everywhere in the disk. Accretion of already formed large embryos is nevertheless possible in the a<0.8AU region. Planetesimal accretion is also strongly affected by an early formed giant planet in the 47 UMa system, with only a small inner region (a<0.3AU) being protected from too high impact velocities. The presence of gas drag could open a small chance for accretion, in particular for relatively large initial planetesimals. Nevertheless, as for Eps. Eridani, a later growth of the giant planet cannot prevent the accretion of lunar-sized embryos in the a<0.8AU area. Additional simulations are also in progress in order to investigate the perturbing effect of the second planet that has been recently discovered around 47 UMa orbiting at 3.73 AU from the central star.
References: Thebault, P., Marzari, F., Scholl, H., ``Terrestrial planet formation in exoplanetary systems with a giant planet on an external orbit", submitted to A&A.