Vanishing space dust baffles astronomers

Astronomers monitoring a cloud of cosmic dust around a star say that the surprising rate at which the haze eventually disappeared suggests that the creation of planets may be a far quicker process than once imagined.

The findings are published in Thursday's edition of the journal Nature.

'The most commonly accepted time scale for the removal of this much dust is in the hundreds of thousands of years, sometimes millions' Inseok Song, University of Georgia

Scientists have long held that miniature particles of dust and gases are the raw material for terrestrial planets, and that the planet builds itself from the surrounding particles as it orbits its host star.

In this instance, the warmed debris swirling around the sun-likestar known as TYC 8241 2652 1 was firstobserved in the Scorpius-Centaurus stellar nursery in the 1980s using a mid-infrared imager.Scientists revisited the star in 2008 andnoted that the infrared emission pattern hadn't changed in decades.But only ayear later, the infrared emission dropped by nearly two-thirds.

By 2010, an examination of the same hot star showed that the surrounding disk of debris had mostly vanished. Such a process for that scale of dust was expected to take eons to complete.

Instead, it appeared to have only taken two to threeyears.

Compared toa magic trick

The scientists compared the phenomenon to a magic trick: Now you see it, now you don't.

"Only in this case we're talking about enough dust to fill an inner solar system, and it really is gone," lead author Carl Melis, a post-doctoral fellow at the University of California inSan Diego, said in a release.

Co-author Inseok Song, an assistant professor of astronomy with the University of Georgia,added that "the most commonly accepted time scale for the removal of this much dust is in the hundreds of thousands of years, sometimes millions."

The conventional theory of "runaway growth"in which planets are formed when gravitational forces clump together enough dust to create something at first the size of a pebble and then eventually a planet could be much more rapid than previous models had calculated, the authors say.

Creation of a planet was generally thought to take hundreds of thousands of years.

"The implication is that if the conditions are right around a star, planet formation can be nearly instantaneous from an astronomical perspective," Song said.

Unfortunately, the star observed by scientists is 450 light years away, meaning that any planet that might have been formed out of the dust would be far beyond the reach of the latest imaging devices.

A second theory accounting for the disappearance of the dust is that the grains were pulled into the star anddestroyed, while a third theory posits that the particles were so tiny that they were pushed out of the star's orbit by photons and dispersed into space.

The team is now looking to monitor dust surrounding other stars to see if they'll be able toobserve a similar event.