Capability Development for A New Generation of Solar System Formation Simulation, 15-9270

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Principal Investigators
Harold F. Levison
S. Alan Stern
David Nesvorn

Inclusive Dates: 07/01/01 - Current

Background - In recent years, NASA has adopted a major scientific theme focused on understanding the origin of planetary systems. In most cases, solar system bodies have formed due to two physical processes: gravitational interactions and physical collisions. Currently, computer simulations can accurately model only one or the other of these due to historically limited computer resources. Yet in most problems in this field, both processes have played important roles in determining what is observed. The objective of this research project is to develop a realistic simulation code (Ultima) capable of growing solid planets in a fully self-consistent way from kilometer planetesimals upward and to demonstrate the predictive power of this code by applying it to explain an outstanding problem in solar system origins - the origin of the Oort cloud.

Approach - SyMBA is a sophisticated planetary dynamics code, which is the basis of Ultima, developed under the leadership of Principal Investigator Harold Levison. This project first called for the development of a new algorithm that will allow SyMBA to track the dynamical effects of myriad small bodies in a planetesimal ensemble. This code will then be married to SwRI's primary collision code, MAC, which has been developed by Alan Stern over a period of 6 years.

Accomplishments - The first major goal of this project is complete - we have developed a dynamical code that accurately accounts for the gravitational interaction of proto-planets with a residual particle disk. Such interaction should be important in late stages of the terrestrial planets formation, presumably dumping planetary eccentricities and inclinations to their present values. (This has been a major failing of planet formation simulations to date.)

In SwRI's new code, the treatment of the interaction between proto-planets and disk, is divided into two regimes: 1) local dynamical drag and 2) distant secular effects. The secular effects are handled using standard techniques. The dynamical drag is handled with an innovative statistical method. The proto-planets are subject to the dynamical friction through a population of tracer particles, each representing a swarm of planetesimals. The team has tested the code in simple situations in which a single proto-planet is emerged in a residual disk. Research staff sampled the available parameter space in these tests. The effect of the dynamical friction on the proto-planet's orbit was analyzed and shown to be consistent with analytic models in regimes where the analytic models have been shown to be valid.

The team has started the algorithm development for the inclusion of collisions into Ultima.

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