Myriad new worlds confound planetary modelers

17 Jun 2002

Astrophysicist Douglas Lin and other theorists are straining to keep up with the whirlwind of planetary discoveries that has blown through astronomy since late 1995. They have stretched their models of how such systems evolve to accommodate a startling variety of planets, from ones with eccentric looping orbits to "hot Jupiters" that practically skim the outer atmospheres of their stars. Even the history of our own solar system is undergoing new scrutiny, Lin reported in a presentation to the American Association for the Advancement of Science this week.

"Planets appear ubiquitous, and planetary systems are extremely diverse," Lin admitted at a special two-day seminar at the AAAS meeting in Seattle. Lin is a professor of astronomy and astrophysics at the University of California, Santa Cruz. "But to form a system that looks like ours, or one that can support the existence of life, may be a rare event."

Lin launched his recent modeling efforts in October 1995 when Swiss astronomers announced the first of the new batch of planets, called 51 Pegasi B. A team at UCSC's Lick Observatory, led by UCSC alumnus Geoffrey Marcy, rapidly confirmed the planet. From the outset its very existence seemed impossible. The Jupiter-sized object raced around its star once every four days, at a distance just one-twentieth that of Earth from our Sun. How could the planet, presumably a giant ball of gas, withstand this blast-furnace orbit? More puzzling still, how did it get there at all?

Lin's conjecture that infant planets can migrate either toward or away from their stars dates to the 1970s, but he doesn't hesitate to call those initial concepts "wild speculations." If his new models are correct, the truth is even weirder. "I never thought the migration could stop, especially so close to the star," he says. "That was a real shocker."