Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.6309s&link_type=abstract
American Astronomical Society, DPS meeting #38, #63.09; Bulletin of the American Astronomical Society, Vol. 38, p.611
Astronomy and Astrophysics
Astronomy
Scientific paper
Planetesimal accretion during planet formation is usually treated as collisionless. However, if the building blocks of protoplanets, planetesimals, are small, of order of a meter in size, then they are likely to collide within the protoplanet's sphere of gravitational influence, leading to the formation of a prograde accretion disk around the protoplanet. The accretion of such an accretion disk results in the formation of protoplanets spinning in the prograde sense with the maximal spin rate allowed before centrifugal forces break them apart. In contrast, collisionless accretion predicts protoplanets with slow retrograde rotation due to planetesimal accretion from a uniform and dynamically cold disk of planetesimals. As a result of semi-collisional accretion, the final spin of a planet after giant impacts is not completely random but is biased toward prograde rotation. The eventual accretion of some of the remaining planetesimals might again be in the semi-collisional regime in which case a significant amount of additional prograde angular momentum would be delivered to the planets in the post-giant impact phase. Semi-collisional accretion seems not only likely to have occurred during planet formation but also offers an explanation for the observed preference for prograde rotation with small obliquities of the terrestrial planets in the Solar System.
Sari Re'em
Schlichting Hilke
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