34th Meeting of the AAS Division on Dynamical Astronomy, May 2003
11 Disks
Oral, Wednesday, May 7, 2003, 8:30-10:30am,

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[11.03] Gas Drag Induced Enhancement of the Growth-Rate of Planetesimals

N. Haghighipour (DTM/CIW)

It is widely accepted that formation of planets starts with collision and coalescence of small solids in a circumstellar disk. Study of the collisional growth of such solids is of utmost of importance since it furthers our understanding of the early stages of planet formation processes.

Recently Inaba and Wetherill have noted that a gas-giant-forming nebula through the core-accretion mechanism, may be gravitationally unstable. In such an unstable rotating gaseous disk, the pressure of the gas does not change monotonically with distance and it maximizes at certain locations. In a previous study I showed that in such a gravitationally unstable environment, when the motions of solids are restricted to the midplane of the nebula, the combined effect of gas drag and pressure gradients causes solids to rapidly migrate toward the locations of the maximum pressure (Haghighipour and Boss, 2003, ApJ, 583, 996). Such rapid migrations have immediate implications for collisional coagulations of small solids and also for enhancement of the growth-rate of planetesimals.

In this paper I 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 such a gravitationally unstable disk. Solid objects in this study are free to move in three dimensions and their collisions, coagulations and accretion are taken into consideration. I will show that gas drag induced collisional coagulation can considerably increase the growth-rate of planetesimals, 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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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.