Herschel Finds Old Star Possibly Making Planets

WASHINGTON -- A star thought to have passed the age when 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.

Herschel is a European Space Agency (ESA) telescope, with science instruments provided by a consortium of European institutes, and with important participation from NASA. 

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. In theory, TW Hydrae is of the age at which giant planets already may have formed. 

Planets are born out of material swirling around young stars and the mass of this material is one factor that controls their formation. Before the new Herschel study, astronomers did not know whether the disk contained enough material to form planets similar to our own.

Astronomers were able to calculate the weight, or mass, of the star's planet-forming disk with the highest precision by using Herschel. The space telescope sees longer-wavelength, or "far," infrared light, allowing it to search for the spectral signature of a gas molecule called hydrogen deuteride. This molecule has one atom made of hydrogen, and one made of a heavier version of hydrogen, called deuterium. It is correlated with regular hydrogen molecules, which are the main gas component of planets. 

"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.

Astronomers did not expect to see so much gas around TW Hydrae, according to 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.

The new method can directly probe the gas that typically goes into making planets, whereas previous techniques were indirect and uncertain.

"Before, we had to use a proxy to guess at what the gas quantity was in the planet-forming disks," said Paul Goldsmith, the project scientist for Herschel at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This is another example of Herschel's versatility and sensitivity yielding important new results about star and planet formation."

Astronomers do not know whether TW Hydrae's large disk will lead to an exotic planetary system with larger and more numerous planets than ours, but the new information helps define the range of possible planet scenarios in the universe.

"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." 

NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at Caltech, supports the United States astronomical community. Caltech manages JPL for NASA. 

For NASA'S Herschel website, visit: http://www.nasa.gov/herschel

For ESA'S Herschel website, visit: http://www.esa.int/SPECIALS/Herschel/index.html

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