For the last 20 years, the best models of planet formation - or how planets grow from dust in a gas disk - have contradicted the very existence of Earth.

These models assumed locally constant temperatures within a disk, and the planets plunge into the Sun.

When the protoplanetary disk begins to dissipate, planets are left behind, safe from impact with their parent star. The results of this research are being presented at the 2010 meeting of the American Astronomical Society in Washington, D.C.

"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.

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. The orbits slowly move inward as the disk dissipates.

Once the gas densities drop low enough for the planets to no longer be influenced by disk, the planets are dropped into an orbit similar to the orbits of planets around the Sun. The radius of the orbit at which a planet is released depends on its mass.

"New simulations show that variations in temperature can lead to regions of outward and inward migration that safely trap planets on orbits around their sun. (Credit: Allfantasyart.com)"

Source: American Museum of Natural History