Tuesday, 21 August 2012

Astronomers have found evidence for a planet being devoured by its star, yielding insights into the fate that will befall Earth in billions of years.

The team uncovered the signature of
a planet that had been "eaten" by
looking at the chemistry of the host
They also think a surviving planet
around this star may have been kicked
into its unusual orbit by the
destruction of a neighbouring world.
Details of the work have been
published in Astrophysical Journal
The US-Polish-Spanish team made the
discovery when they were studying
the star BD+48 740 - which is one of a
stellar class known as red giants. Their
observations were made with the
Hobby Eberly telescope, based at the
McDonald Observatory in Texas.
Rising temperatures near the cores of
red giants cause these elderly stars to
expand in size, a process which will
cause any nearby planets to be
"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 co-author Prof Alexander
Wolszczan from Pennsylvania State
University in the US.
Lithium boost
The first piece of evidence for the
missing planet comes from the star's
peculiar chemical composition.
Spectroscopic analysis of BD+48 740
revealed that it contained an
abnormally high amount of lithium, a
rare element created primarily during
the Big Bang 14 billion years ago.
Lithium is easily destroyed in stars, so
its high abundance in this ageing star
is very unusual.
"Theorists have identified only a few,
very specific circumstances, other
than the Big Bang, under which
lithium can be created in stars," Prof
Wolszczan explained.
"In the case of BD+48 740, it is
probable that the 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."
The second piece of evidence
discovered by the astronomers is the
highly elliptical orbit of a newly
discovered planet around the red
giant star. The previously undetected
world is at least 1.6 times as massive
as Jupiter.
Co-author Andrzej Niedzielski of
Nicolaus Copernicus University in
Torun, Poland, said that orbits as
eccentric as this one are uncommon
in planetary systems around evolved
"In fact, the BD+48 740 planet's orbit
is the most elliptical one detected so
far," he added.
Because gravitational interactions
between planets are often
responsible for such peculiar orbits,
the astronomers suspect that the dive
of the missing planet toward its host
star before it became a giant could
have given the surviving massive
planet a burst of energy.
This boost would have propelled it
into its present unusual orbit.
Team member Eva Villaver of the
Universidad Autonoma de Madrid in
Spain commented: "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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