U.S.-Japan Cooperative Research: Structure and Evolution of Protogiant Planet Formation

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This award will provide support for a two year cooperative research project on protogiant planet formation, between Professor Peter H Bodenheimer and colleagues at the Lick Observatory, University of California, Santa Cruz, and Professor Satoru Ikeuchi and colleagues from the National Astronomical Observatory, Japan. The formation of the solar system is one of the most important unsolved problems in astrophysics and planetary science. Recently accumulated observational data on the existence and evolution of protostellar disks around young stars seem to indicate that systems, similar to those that lead to the formation of the solar system, may be abundant, and that the formation of planetary systems may be an ongoing process instead of a long-ago event. The aim of this project is to is to undertake a theoretical investigation of the formation of giant planets to help interpret these observations. Giant planets are thought to have been initiated by the accumulation of small solid particles that existed in the primordial solar nebula. After the build up of this core to a few earth masses, it is believed that the protoplanet was able to gravitationally capture relatively large amounts of gas from the nebula, and that the final formation stages were dominated by gas accretion. It is intended during this project to analyze this process of gas accretion, using a three-dimensional hydrodynamic computer code. Through this analysis, it is hoped to determine the mass accretion rate as a function of time, the rate of accretion of spin angular momentum as a function of time, and the change in the location of the protoplanetary orbit as a function of time. Both the US and Japanese researchers involved in this collaboration have made intensive investigations into the general problem of the origin of the solar system and are highly regarded for their past research in the subject area. The research skills of the two groups are very complementary. If the research is successful it should give us some insight into how the final mass of giant planets was determined and how the regular satellite systems originated, and should provide a very valuable theoretical component to our understanding of the process of planet and solar system formation.