Astronomers Find Evidence of Planet Being Destroyed by Its Aging Star

Posted on August 21, 2012

A team of international astronomers have reported the first evidence of a planet being destroyed by its aging star. The evidence indicates that the missing planet was devoured as the star began expanding into a red giant. The star, named BD+48 740, is older than the Sun with a radius about eleven times bigger.

Alex Wolszczan, an Evan Pugh Professor of Astronomy and Astrophysics at Penn State University, says, "A similar fate may await the inner planets in our solar system, when the Sun becomes a red giant and expands all the way out to Earth's orbit some five-billion years from now."

The astronomers also discovered a massive planet in a surprisingly elliptical orbit around the same red-giant star. Wolszczan and the team's other members, Monika Adamow, Grzegorz Nowak, and Andrzej Niedzielski of Nicolaus Copernicus University in Torun, Poland; and Eva Villaver of the Universidad Autonoma de Madrid in Spain, detected evidence of the missing planet's destruction while they were using the Hobby-Eberly Telescope to study the aging star and to search for planets around it. The evidence includes the star's peculiar chemical composition, plus the highly unusual elliptical orbit of its surviving planet.

Adamow says, "Our detailed spectroscopic analysis reveals that this red-giant star, BD+48 740, contains an abnormally high amount of lithium, a rare element created primarily during the Big Bang 14 billion years ago. Theorists have identified only a few, very specific circumstances, other than the Big Bang, under which lithium can be created in stars."

The second piece of evidence is the highly elliptical orbit of the huge planet discovered orbiting the star. The astronomers suspect that the dive of the missing planet toward the star before it became a giant could have given the surviving massive planet a burst of energy, throwing it into an eccentric orbit like a boomerang.

Villaver says, "Catching a planet in the act of being devoured by a star is an almost improbable feat to accomplish because of the comparative swiftness of the process, but the occurrence of such a collision can be deduced from the way it affects the stellar chemistry. The highly elongated orbit of the massive planet we discovered around this lithium-polluted red-giant star is exactly the kind of evidence that would point to the star's recent destruction of its now-missing planet."

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