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| Artist's concept illustrates an icy planet-forming disk around a young star called TW Hydrae. [Image Credit: NASA/JPL-Caltech] |
Washington: A star thought to have passed the age at which it can form
planets may in fact be creating new worlds. The disk of material surrounding
the surprising star called TW Hydrae may be massive enough to make even more
planets than we have in our own solar system.
The findings were
made using the European Space Agency's Herschel Space Telescope, a mission in
which NASA is a participant.
At roughly 10 million
years old and 176 light years away, TW Hydrae is relatively close to Earth by
astronomical standards. Its planet-forming disk has been well studied. TW
Hydrae is relatively young but, in theory, it is past the age at which giant
planets already may have formed.
"We didn't
expect to see so much gas around this star," said Edwin Bergin of the
University of Michigan in Ann Arbor. Bergin led the new study appearing in the
journal Nature. "Typically stars of this age have cleared out their
surrounding material, but this star still has enough mass to make the
equivalent of 50 Jupiters," Bergin said.
In addition to
revealing the peculiar state of the star, the findings also demonstrate a new,
more precise method for weighing planet-forming disks. Previous techniques for
assessing the mass were indirect and uncertain. The new method can directly
probe the gas that typically goes into making planets.
Planets are born out
of material swirling around young stars, and the mass of this material is a key
factor controlling their formation. Astronomers did not know before the new
study whether the disk around TW Hydrae contained enough material to form new
planets similar to our own.
"Before, we had
to use a proxy to guess the gas quantity in the planet-forming disks,"
said Paul Goldsmith, the NASA project scientist for Herschel at NASA's Jet
Propulsion Laboratory (JPL) in Pasadena, California. "This is another
example of Herschel's versatility and sensitivity yielding important new
results about star and planet formation."
Using Herschel, they
were able to take a fresh look at the disk with the space telescope to analyze
light coming from TW Hydrae and pick out the spectral signature of a gas called
hydrogen deuteride. Simple hydrogen molecules are the main gas component of
planets, but they emit light at wavelengths too short to be detected by
Herschel. Gas molecules containing deuterium, a heavier version of hydrogen,
emit light at longer, far-infrared wavelengths that Herschel is equipped to
see. This enabled astronomers to measure the levels of hydrogen deuteride and
obtain the weight of the disk with the highest precision yet.
"Knowing the
mass of a planet-forming disk is crucial to understanding how and when planets
take shape around other stars," said Glenn Wahlgren, Herschel program
scientist at NASA Headquarters in Washington.
Whether TW Hydrae's
large disk will lead to an exotic planetary system with larger and more numerous
planets than ours remains to be seen, but the new information helps define the
range of possible planet scenarios.
"The new results
are another important step in understanding the diversity of planetary systems
in our universe," said Bergin. "We are now observing systems with
massive Jupiters, super-Earths, and many Neptune-like worlds. By weighing
systems at their birth, we gain insight into how our own solar system formed
with just one of many possible planetary configurations."