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Fried Planets -- presented by Science@NASA
Astronomers have just 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.
Until then, for breaking science news, stay tuned to science.nasa.gov