Planetary Accumulation with a Continuous Supply of Planetesimals |
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Authors: | George W Wetherill Satoshi Inaba |
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Institution: | (1) Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC, 20015 |
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Abstract: | Previous calculations of the accumulation of small (∼10 km) planetesimals at ∼1 AU to form Mars-sized bodies assumed that
the initial assemblage of planetesimals were all present at the outset. This is an obviously reasonable assumption in systems
in which the time scale for growth time of ∼1026 g planetary bodies is long compared to estimates of the evolutionary time scale of a protosolar disk, as was the case in
the pioneering work of Safronov (1969). It is now found that as a result of the preplanetary assemblage being unstable with
respect to the runaway growth of the largest bodies, this is unlikely to be the case. The more realistic alternative of adding
the initial planetesimals on a ∼105 year time scale is considered here, as well as the consequences of the initial planetesimals being considerably smaller than
those assumed previously. It is found that although the time scale for runaway growth is now actually controlled by the availability
of planetesimals, for planetesimal production time scales of ∼105 yrs, the final consequences are very similar. These calculations do show, however, that as a consequence of continuous infall
during the runaway growth process, the late initial planetesimals are likely to be catastrophically disrupted by mutual collisions.
For this reason, a more detailed treatment of the growth of planetesimals into planetary embryos will require a better understanding
of the difficult problem of formation of the initial planetesimals themselves.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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