Astronomers
say they have discovered the youngest planet to date circling a sun-like star,
a find that will be a boon to the field of planet-formation theory.
The
extrasolar planet is an estimated 8 million to 10 million years old, a mere
toddler compared to Earth, which is 4.5 billion years old. Until now, the
researchers say, no planet younger than 100 million years old has been detected
circling a sun-like star.
"It
means we're opening up a new field of trying to find planets around very young
stars," said Alan Boss, a planet-formation theorist at the Carnegie
Institution of Washington. "So it's the very first example, and we hope
there will be a lot more." Boss was not involved in the discovery.
The newly
found world is so infantile that it resides in the star's "protoplanetary
disk," a ring of gas and dust circling the star. It has been catalogued as
TW Hya b.
"This
demonstrates that planets can form within 10 million years, before the disk has
been dissipated by stellar winds and radiation," the researchers write in
the Jan. 3 issue of the journal Nature.
Weighing in
at nearly 10 Jupiter masses, the planet circles at a distance of .04
Astronomical Units (AU) from its host star, TW Hydrae, in the constellation
Hydra. One AU is the average distance between the Earth and sun.
The gassy
"hot Jupiter" takes 3.56 days to orbit its star. The host star is
located 180 light-years away from Earth.
Planets are
thought to form within disks of dust and gas around newly born stars. Catching
a planet
in its childhood can give astronomers lots of information about how planets
materialize.
"The
discovery shows that what we always call as 'protoplanetary' disks are indeed
protoplanetary; they form planets," study researcher Johny Setiawan of the
Max-Planck Institute for Astronomy in Germany told SPACE.com.
"There are many 'protoplanetary' disks detected around young stars, but no
planets so far have been detected within such young systems."
Around some
young star systems, however, astronomers have found signs
of planets by noting clear lanes of dust within the disks. In these cases,
it's presumed that young planets are forming and have scooped up the dust, but
the planets themselves have not been detected.
Setiawan
and colleagues discovered their new world by measuring a wobble in the host
star due to the gravitational tug from the orbiting planet. This so-called
radial-velocity method is great at detecting extrasolar planets, but it also
can produce false positives — suggesting a planet is there when in fact the data
owe to some other object or phenomenon.
That's
particularly true in young star systems. For one, nascent stars are incredibly
active and their changing outer atmospheres can at the very least make for
background noise. In addition, if the star rotates about its axis, that can be
problematic.
"There
are lots of other things going on in these young stars that could give you a
false positive, where you think you're seeing a planet but you're actually
seeing some other stellar activity," Boss said in a telephone interview.
Boss thinks
the discoverers ruled out these non-planet signals. "They've done a good job of trying to
address those worries," he said.
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