Formation of Gas Giant Satellites

Details Formation of Gas Giant Satellites Formation of Gas Giant Satellites

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p21b..01c&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P21B-01

Astronomy and Astrophysics

Astronomy

5205 Formation Of Stars And Planets, 6218 Jovian Satellites, 6265 Planetary Rings, 6280 Saturnian Satellites, 6290 Uranian Satellites

Scientific paper

The Jovian and Saturnian regular satellites are believed to have accreted within circumplanetary disks of gas and solids. Such disks probably existed during the final stages of gas planet accretion, because gas inflowing from solar orbit that contained too much angular momentum to fall directly onto the planet would have instead flowed into circumplanetary orbit. As a circumplanetary gas disk viscously diffuses, most of its mass is accreted by the planet while most of its angular momentum (contained in a small fraction of its mass) is transferred outward and escapes. The gas planet disks would have been continually replenished by any ongoing inflow of nebular gas, allowing the disks to persist until the nebula itself dissipated. Here I will discuss a model [1,2,3] in which gas giant satellites form within inflow-supplied circumplanetary disks. Small solids carried into the disk by the inflowing gas provide the raw material for accreting satellites. A satellite grows until it reaches a critical mass for which the timescale for its further growth is comparable to the timescale for its orbit to decay via gravitational interactions with the gas disk. Once a satellite reaches this critical mass (comparable to that of Titan and the Galilean satellites), its orbit spirals inward and if inflow to the disk continues, the satellite will be lost to collision with the planet while a new one grows in its place. The current Jovian and Saturnian satellites represent the last surviving generation of satellites that formed as gas inflow to the circumplanetary disks ended. As the rate of inflow wanes, the disk cools, allowing the final satellites to incorporate substantial ices. For reasonable conditions, this model can account for the general structure (i.e., masses, numbers, and orbital spacings of the large satellites) and overall compositional trends in both the Jovian and Saturnian satellite systems. It implies that the current large satellites accreted slowly (in > 5 × 105 yr), within low-density, 'gas-starved' disks. The model also produces satellite systems that resemble that of Uranus, although its applicability to Uranus depends on how the planet acquired its obliquity. [1] Canup, R.M. & W.R. Ward, Astron. J. 124, 3404 (2002); [2] Canup, R.M. & W.R. Ward, Nature 441, 834 (2006). [3] Ward, W.R. & R.M. Canup, submitted (2008). Support from NASA's OPR and PGG programs is gratefully acknowledged.

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