How Earth Survived Birth
New Simulation Reveals Planet Migration Prevents Plunge into Sun
“We are trying to understand how planets interact with the gas disks from which they form as the disk evolves over its lifetime,” says Mordecai-Mark Mac Low, Curator of Astrophysics and Division Chair of Physical Sciences at the Museum. “We show that the planetoids from which the Earth formed can survive their immersion in the gas disk without falling into the Sun.”
During the birth of a star, a disk of gas and dust forms. The midplane of this dusty disk is opaque and cannot quickly cool by radiating heat to outer space. Until recently, no one has included temperature variation in models of planet formation. Co-author Sijme-Jan Paardekooper of the University of Cambridge ran new simulations like that most recently published online (http://arxiv.org/abs/0909.4552). His work shows that the direction of migration of low-mass planets in disks depends on the detailed temperature structure of the disk. This key insight lays the groundwork for the current work.
The American Astronomical Society presentation incorporates the results of Paardekooper’s local models into the long-term evolution of the temperature and density structure of a protoplanetary disk. The result of the simulation is that, over the lifetime of a disk, planets get trapped in orbits between regions of inward and outward migration.
“We used a one-dimensional model for this project,” says co-author Wladimir Lyra, a postdoctoral researcher in the Department of Astrophysics at the Museum. “Three dimensional models are so computationally expensive that we could only follow the evolution of disks for about 100 orbits -- about 1,000 years. We want to see what happens over the entire multimillion year lifetime of a disk.”
Mac Low presented this research at the American Astronomical Society meeting in Washington, D.C., on January 6. A research paper is currently submitted to The Astrophysical Journal, authored by Lyra, Paardekooper, and Mac Low. This research was funded by the American Museum of Natural History, the National Science Foundation, and NASA.