|Courtesy of Gabi Perez/IAC/ESO|
The Orion nebula, where large groups of stars are being born, would seem the ideal place to manufacture planets. Indeed, 90 percent of young stars there possess dusty disks that could potentially clump into new worlds. But making a planet, it turns out, isn't all that easy to do. Intense radiation streaming from the nebula's brightest infant stars can stop the process in its tracks, says astronomer C. Robert O'Dell of Vanderbilt University in Nashville, Tennessee. "Radiation evaporates away the disks in a few hundred thousand years or less," he says, leaving little or no time for planets to coalesce.
In other cases, when planets do manage to form, they must contend with their own suns. Garik Israelian of the Astrophysics Institute of the Canary Islands and his colleagues have found evidence that at least one star has consumed a planet. The team looked at a mature, sun-like star called HD82943, which has two giant planetary companions. The star contains traces of lithium-6, a metal that is normally burned up in the earliest stages of star formation. Israelian believes the metal came from a planet that migrated too close and was engulfed by the star. "It could be that this is a common phenomenon," he says. In fact, it will almost surely happen here in about 7 billion years, when the sun balloons into a red giant star and vaporizes the inner planets, possibly including Earth.