Washington, Aug 21 (IANS): Astronomers have come by the first ever evidence of an ageing star devouring its own planet especially after it expanded into a "red giant", the equivalent of old 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 and study co-author.

Wolszczan also discovered the first planet ever found outside our solar system. Astronomers 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 11 times bigger, the Astrophysical Journal Letters reports.

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 ageing star and search for planets around it.

The evidence includes the star's peculiar chemical composition, plus the highly unusual elliptical orbit of its surviving planet, according to a Penn statement.

"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 presence in this older star is so unusual. "Theorists have identified only a few, very specific circumstances, other than the Big Bang, under which lithium can be created in stars," Wolszczan added.

"In the case of BD+48 740, it is probable that lithium production was triggered by a mass the size of a planet that spiralled into the star and heated it up while the star was digesting it," said Wolszczan.