Astronomers eyeing stars seek new solar systems

The two bright debris disks were observed by the Hubble Space Telescope.
San Francisco Chronicle
Astronomers studying two nearby stars in the Milky Way galaxy have discovered rings of frozen rocky debris surrounding them that strikingly resemble the ring of debris around our own solar system known as the Kuiper Belt.
They are now on the hunt for signs that at least one of those stars may be an alien sun with a solar system all its own containing one or more planets where life could develop, according to UC Berkeley research astronomer Paul Kalas.
The still-mysterious Kuiper Belt surrounds our own solar system, and hundreds of thousands of icy objects abide there, along with the many short-period comets that frequently flash across our skies. The newly discovered debris disks might well surround similar solar systems, Kalas and his colleagues say.
On Thursday, the Astrophysical Journal posted an online version of a new report by Kalas and his colleagues, saying observations by the Hubble Space Telescope have for the first time revealed details of the exceptionally bright debris disks surrounding two of 22 stars that the Hubble's new Advanced Camera has been surveying.
To Kalas' delight, the posting came on the same day that NASA -- after two days of weather delays -- launched its New Horizons spacecraft to explore Pluto, our most distant planet, for the first time and take a close look at other objects in the Kuiper Belt.
"We still know so little about that region on the edge of our solar system," Kalas said in an interview, "but what we find there could help us understand the debris disks around these other stars where habitable zones may exist for planets capable of supporting life."
About two stars
The two stars are only 60 light years away, and bear no names, but they have often been studied by other astronomers through other telescopes on Earth and in orbit. They are designated as HD53143 and HD139664.
The first of the two stars is estimated to be about a billion years old and the second about 300 billion years old. Kalas said these are only rough estimates based on the stars' chemical composition and their X-ray emissions. They could well be much, much older or possibly younger, he said.
The disk around each of the stars seems to have a central area that has been cleared of the icy debris, and that's where entire systems of planets may well exist, Kalas said.
Tough challenge
Searching for them in the space between the innermost edges of the two debris rings poses an extremely difficult challenge, Kalas said, but he and his colleagues will be heading for Hawaii next month to probe that space inside the debris rings, using the adaptive optics aboard the sophisticated Keck telescopes.
The Hubble also will focus on the two stars to aid the planet search.
"There could well be signs that planetary systems have already formed there," Kalas said, "and if any planets are at the right distance from their suns, they could well be habitable and capable of supporting life."
In our own solar system the Earth is the only planet known to hold life, and it lies about 93 million miles from sun -- a distance known as one astronomical unit, or 1 AU. The star known as HD 139664 is somewhat larger than our own sun and, therefore, any habitable planet there could probably be as much as 5 AU distant from the star, Kalas said.
Clear in visible light
About 100 other stars in the Milky Way are known to be surrounded by debris disks, and the first one was detected 20 years ago.
But the two reported Thursday were the first to be clearly observed in visible light, and they were first detected during a two-year survey by the Hubble.
A deeper understanding of the rings of icy rocks, dust and other debris surrounding stars like the two that Hubble has probed -- and a deeper understanding of the Kuiper Belt that the New Horizons spacecraft will begin to probe when it reaches Pluto 10 years from now -- should help scientists learn more about how the solar system itself was formed some 4.5 billion years ago, Kalas said.
His colleagues in the report were astronomers James Graham and Michael Fitzgerald of UC Berkeley and Mark Clampin of NASA's Goddard Space Flight Center in Greenbelt, Md.
Copyright 2006 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.