10-million-year-old star possibly making new planets

Scientists have discovered that an old star - 176 light years away from Earth - thought to be past its prime may still be creating new planets.

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, NASA said in a statement.

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.

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 lead researcher Edwin Bergin of the University of Michigan in Ann Arbor.

"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.

Using Herschel, researchers were able to take a fresh look at the disk with the space telescope to analyse 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 programme scientist at NASA Headquarters in Washington.