Flurry of Planets Found at Full Tilt: Violent Interactions May Have Shaped Extrasolar Systems
Cowen, Ron, Science News
Call them the wrong-way planets. Several giant, extrasolar planets, all residing within sizzling distance of their parent stars, have orbits so tilted that the planets travel backward relative to their parent stars' rotation, new studies reveal. The misalignments attest to rough-and-tumble histories and may suggest that life flourished on Earth because the solar system avoided the brunt of close gravitational encounters between planets.
According to the most popular formation theory, planets coalesce from a swirling disk of gas and dust that surrounds young stars. Since the disk rotates in the same direction as the star, the planets spawned should revolve in that direction as well. But in an overcrowded system, where a gravitational game of billiards is all but inevitable, orbits can get scrambled. A close encounter between planetary siblings can push one body outward while flinging the other inward, elongating and tilting the inner planet's orbit.
In this scenario, the Earth's solar system may have been unusually lucky. Either it avoided catastrophic gravitational encounters between massive planets or it suffered such interactions so long ago that most of the planets had time to resettle into nearly circular orbits with little or no tilt, says Frederic Pont of the University of Exeter in England.
"The presence of advanced life on Earth may be contingent on our planetary system having avoided the brunt of planet-planet scatter," keeping Earth on a circular, Goldilocks-style orbit--neither too hot nor too cold for known forms of life, he speculates.
In one of the new studies, posted online August 24 at arXiv.org, Pont and colleagues examined the orbit of the planet COROT-lb. …