Baby Star 'Winks,' Hints at Nascent Planet System
Wed Jun 19,12:51 PM ET

By Deborah Zabarenko

WASHINGTON (Reuters) - A Sun-like star just out of infancy has winked at astronomers, indicating its eclipse by cosmic dust and rocks, the stuff of which planets like Earth could possibly form, scientists reported on Wednesday.

A sun-like star just out of infancy has winked at astronomers, indicating its eclipse by cosmic dust and rocks, the stuff of which planets like Earth could possibly form, scientists reported June 19, 2002. This illustration shows a possible model of what this eclipse may look like. (Geoffrey Bryden/NRC Research Associate/Jet Propulsion Lab via Reuters)

The star, located in the Unicorn constellation about 2,400 light-years from Earth, disappeared from view for regular periods of about 48 days over the past six years. Its disappearance suggested an eclipse, but not a typical one caused by an intervening planet, star or moon.

Only a collection of smaller objects, like dust and rocks, could cause the long eclipse the astronomers saw.

Known as KH 15D, the star is only about 3 million years old, a prime age for monitoring by astronomers interested in our solar system's planet-forming past.

"We've monitored thousands of these stars over the years and this is the only that behaves this way," said astronomer William Herbst of Wesleyan University, in Connecticut.

"Essentially the star winks at us," Herbst told reporters at a meeting on extrasolar planets at the Carnegie Institution in Washington.

The dust that caused the wink is different from the fine interstellar dust that is distributed throughout the cosmos, Herbst said. Its particles are bigger, indicating that it is clumping into what astronomers call a protoplanetary disk -- the disk from which planets can form.

"Is there a mass in here that is somehow sculpting the obscuring clouds so that it's producing these rings of material which then circle around the star and alternately block the object? We think that's very possible," Herbst said.

COSMIC TODDLER

There could be two blobs circling the star, or just one, but there is no confirmation as yet of exactly what could be causing this kind of disk to form, said Herbst's colleague Catrina Hamilton.

At just 3 million years old, KH 15D is a cosmic toddler barely out of infancy. By contrast, our solar system is thought to be about 4.5 billion years old. However, some astronomers believe the planets may have begun forming when the Sun was a few million years old.

The disk is forming quite close to the star, closer than the planet Mercury is to the Sun.

"The star is ... like the Sun was when it was 3 million years old, so the processes that are going on in this inner disk region, where terrestrial planets would be forming ... could be analogous to what was going on with the formation of Earth," Herbst said.

The discovery was made with a relatively small 24-inch telescope, so it could well be the subject of other astronomers' scrutiny with other, larger instruments.

"I think this gives us a whole new window into how planets form and it's one that a lot of astronomers will be trying to exploit with their telescopes in the next few years," said NASA ( news - web sites) astronomer Steve Maran. "We're finally seeing the planetary formation system in action."

"I think this object might turn out to be something of a Rosetta Stone for deciphering some of the mysteries of planet formation," said Alan Boss of the Carnegie Institution.

Astronomers have already detected dozens of so-called extrasolar planets, but this is the first time they have looked at the apparent formation of a protoplanetary disk.

The new research was performed by an international team that included astronomers from Uzbekistan, Israel and Germany as well as several U.S. institutions.