Planetesimal Capture as a Clue to the Formation of Gas-Giants
Prior to the last stage of the formation of a giant planet, the core of this object is
surrounded by an extended gaseous envelope. The models of giant planet formation
suggest that, to the first order, this envelope should have a strictly solar composition.
However, measurements by Galileo spacecraft have indicated a higher-than-solar
abundance of heavy elements in the atmosphere of Jupiter. During giant planet
formation, the Solar System is populated by km-sized and larger bodies, many
of which may scatter into the giant planet's proto-atmosphere where their
dynamics is affected by gas drag. As a result, these objects may be captured entirely,
or may deposit some of their materials in passing through the envelope.
We have studied the interactions of planetesimals with the gaseous envelope
of an evolving giant planet, and have computed the efficiency of their capture
and of the deposition of different elements. We present the results of our study
and discuss the relation between the physical and dynamical properties of planetesimals,
and the rate of their mass deposition. Since a planet formed by the disk instability
scenario will have very different capture cross-sections over time than a planet
formed by the core accretion model, our study should help to differentiate
between these two scenarios, as well.