Dr. Sally Dodson-Robinson
Caltech
University of Florida Astronomy Colloquium - Feb. 4th, 2009
Chemistry and dynamics of the solar nebula
To date, there is no solar nebula model that can successfully account for the formation of Saturn, Uranus or Neptune within the observed 2-3 Myr lifetimes of protoplanetary disks. Since solid accretion rate is directly proportional to the available planetesimal surface density, one way to speed up planet formation is to take a full accounting of all the planetesimal-forming solids present in the solar nebula. By combining a viscously evolving protostellar disk with a kinetic model of ice formation, I calculate the solid surface density in the solar nebula as a function of heliocentric distance and time. I find three effects that strongly favor giant planet formation: (1) a decretion flow that brings mass from the inner solar nebula to the giant planet-forming region, (2) recent lab results showing that the ammonia and water ice lines should coincide, and (3) the presence of a substantial amount of methane ice in the trans-Saturnian region. This solar nebula model allows both Saturn and Jupiter to form within 3.5 Myr without invoking arbitrary Type I migration rates. I also discuss the location of ice lines and their movement through the solar nebula, and provide new constraints on the initial disk configuration from gravitational stability arguments.