AAS 202nd Meeting, May 2003
Session 55 Solar Systems to Galaxies
Oral, Thursday, May 29, 2003, 10:00-11:30am, 108/109

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[55.02] Gas Drag Induced Coalescence of Small Solids in a Gravitationally Unstable Nebula

N. Haghighipour, A. P. Boss (DTM/Carnegie)

It has recently been noted by Inaba and Wetherill that a nebula massive enough to form gas-giant planets through the core-accretion mechanism, is likely marginally gravitationally unstable. The alternative approach, namely, the disk instability scenario, implies that such an instability could lead to rapid formation of gas-giant planets. It is therefore quite important to study the dynamics of small solids in such an environment and investigate the implications for their collisional coagulations.

We present the results of an extensive numerical study of the orbital evolution and growth of small solids, ranging from micron-sized dust grains to km-sized objects in a gravitationally unstable nebula. In such an unstable rotating gaseous disk, the pressure of the gas does not change monotonically with distance and it maximizes at certain locations. We show that the combined effect of gas drag and pressure gradients causes solids to rapidly migrate toward the locations of the maximum pressure. Such rapid migrations have immediate implications for collisional coagulations of small solids and also for the enhancement of the growth-rate of planetesimals. We show that gas drag can considerably increase the rate of coalescence of small solids, in particular, when the objects grow to sizes of 10 cm to 1 m.

Support for this work through NASA's PGG program and NASA Astrobiology Institute is greatly acknowledged.

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