Earth may be devoured by ageing sun 5 billion years from now

The finding is based on the discovery of the first evidence of a planet's destruction by its ageing star.

The evidence indicates that the missing planet was devoured as the star began expanding into a "red giant" - the stellar equivalent of advanced age.

"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," said Alex Wolszczan, Professor of Astronomy and Astrophysics at Penn State University.

Wolszczan, who is one of the members of the research team, also is the discoverer of the first planet ever found outside our solar system.

The astronomers also discovered a massive planet in a surprisingly elliptical orbit around the same red-giant star, named BD+48 740, which is older than the Sun with a radius about eleven times bigger.

Wolszczan and colleagues from Nicolaus Copernicus University in Torun, Poland; and 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 ageing 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.

"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," Adamow said.

Lithium is easily destroyed in stars, which is why its abnormally high abundance in this older star is so unusual.

The second piece of evidence discovered by the astronomers is the highly elliptical orbit of the star's newly discovered massive planet, which is at least 1.6 times as massive as Jupiter.

Because gravitational interactions between planets are responsible for such peculiar orbits, 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.

The paper describing this discovery is published in the early edition of the Astrophysical Journal Letters.