Originally created 06/20/02

Astronomers spot new solar system



WASHINGTON -- A young, sun-like star with orbiting blobs of dust and rock may be forming planets, giving astronomers their first chance to observe the evolution of a planetary system like our own.

The star, named KH 15D, is unique in astronomy because it is periodically obscured by clouds of matter that orbit between the star and viewers on Earth, said William Herbst of Wesleyan University in Middletown, Conn.

Herbst said Wednesday the orbiting material may be building planets, perhaps following the same evolutionary process that is thought to have formed the Earth and its sister planets.

"The processes that are going on in this inner disk region could be analogous to what was going on in the formation of the Earth," said Herbst. "It could shed light on our origins by helping us to understand how our Earth and the planets in the solar system came to be."

Although many distant stars have been observed to have orbiting debris, Herbst said KH 15D "is the only one that behaves in this way" and the only one seen with matter orbiting so close to the central star.

"The star is eclipsed by material that is circling it," said Herbst. "Essentially, the star winks at us."

The eclipse comes at very regular intervals, with the star dimming over a two-day period and then brightening again following the eclipse.

"It stays bright and then every 48.36 days it drops to a mere shadow of its former self - only 4 percent of its normal brightness," said Herbst.

Catrina Hamilton, also of Wesleyan University, said there is evidence there may be two "blobs" of material in directly opposing orbits. This means that as one cloud of debris eclipses the star, from the viewpoint of Earth, the other cloud of debris would be on the opposite side of the star.

KH 15D is 2,400 light years from Earth. A light year is about 5.8 trillion miles.

The Wesleyan astronomers presented their findings Wednesday at a meeting of astronomers who are conducting research on extrasolar planets - planets that orbit stars other than our sun. So far, astronomers have found almost 100 such planets, nearly all of them large gaseous bodies the size of Jupiter or bigger.

Alan Boss, an astronomer at the Carnegie Institution in Washington, said the Wesleyan team's discovery of KH 15D gives astronomers a unique opportunity to gain understanding about the life and times of planets such as those in the sun's family.

"It is not an exact analogue of our own system," said Boss, but KH 15D will allow astronomers to observe key phases of planetary system formation.

KH 15D is a young star, only about three million years old, and it already has evidence that a single giant gaseous planet, rather like Jupiter, has formed and is circling the star closer than the planet Mercury orbits the sun, the astronomers said.

If further study proves there is a planet, said Herbst, it suggests planet formation can start very early after a star is born.

Herbst said an analysis of the starshine from KH 15D shows that when it is eclipsed, the dimmed light is actually bluer than when it is shining brightly. Usually when star or sun light is dimmed by small dust particles, such as at sunset, the light appears to be red. This is because small particles tend to more readily scatter the blue part of the light spectrum, leaving more red to be seen. The blue light from KH 15D suggests the light is being reflected off larger objects in the disk and not just small dust particles, he said.

In order for the debris to be formed into clumps suggests that some massive object, such as a planet, is gravitationally forcing the smaller particles into a blobs, like a shepherd keeps a flock of sheep in one group. Without this shepherding effect, said Herbst, the debris would be evenly distributed around the orbit and not be clumped in a way that causes eclipses.

On the Net:

KH 15D: http://www.astro.wesleyan.edu/kh15d