Oct. 25, 2012: An international team of astronomers has caught a star in the act of devouring one of its planets. BD+48 740, a red giant they observed using the 9.2-meter Hobby-Eberly Telescope at the McDonald Observatory in Texas, appears to have the fumes of a scorched planet in its atmosphere. This is consistent with a rocky world, recently destroyed.
Could the same thing happen to Earth?
Yes indeed, says Alex Wolszczan, a member of the research team from Penn State University: "A similar fate may await the inner planets in our solar system when the sun becomes a red giant some five billion years from now."
Researchers who specialize in stellar evolution have long known that the inner planets are in danger. The trouble starts in the distant future when the sun's core runs out of hydrogen fuel for nuclear fusion. To keep the fires burning, the sun will begin to fuse hydrogen outside the core, in a layer closer to the stellar surface. This will turn the sun into a red giant, at least 200 times wider than it is today. Mercury, Venus, Earth and possibly even Mars could be engulfed.
The fate of Earth is not a certainty, however. Some researchers believe that Earth's orbit might spiral outward, keeping the planet at a safe distance from the approaching inferno. This could happen if solar winds carry away a significant fraction of the sun's mass in the years leading up to the red giant phase.
On the other hand, the sun might expand so quickly that our planet has no chance to escape. Earth would get caught in the sun's rapidly advancing atmosphere and spiral inward to oblivion.
Observations of red giant BD+48 740 lend credence to the second possibility.
"Our detailed spectroscopic analysis of BD+48 740 reveals that the red giant contains an abnormally
high amount of lithium," says Monika Adamow who led the study at the Nicolaus Copernicus University in Torun, Poland.
Because lithium is easily destroyed in stars, finding lots of it in an old red giant is unexpected. The most likely source is a planet. Wolszczan explains: "It is probable that the lithium production in BD+48 740 was triggered by a mass the size of a planet that spiraled into the star and heated up while the star was digesting it."
The team found another piece of evidence, too. BD+48 740 has a gas giant planet 1.6 times bigger than Jupiter which has not yet been devoured. The big planet has a highly elliptical orbit. In fact, it is the most elliptical orbit ever found for a planet around an older star. Its orbit, which almost surely started out circular, was probably altered by some catastrophic event--like its star having an inner planet for lunch.
One day, he says, our own solar system may end up the same way. In five billion years, the fried planet could be Earth.
The original research of Adamov et al may be found in their article "BD+48 740 - Li overabundant giant star with a planet. A case of recent engulfment?"