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Scientist says possibility exists for life elsewhere

Posted on: Friday, 4 July 2003, 06:00 CDT

Another planet has been added to the list of 100 or so worlds that astronomers have discovered around distant stars - but unlike all those other planets, this one is in a solar system that may be capable of supporting another Earth.

The discovery, which was announced today at a conference in Paris and is to be published in an upcoming issue of the Astrophysical Journal, marks the first time that the search for extrasolar worlds has produced a planet orbiting in a system so strikingly similar to our own.

"This planet and its orbit are quite reminiscent of Jupiter," said Brad Carter, an astronomer at the University of Southern Queensland and lead author of the upcoming Astrophysical Journal article.

The planet, which is a gas giant about twice the size of Jupiter, travels around a star very much like our own sun in a nearly circular orbit about three-fifths the size of our solar system's resident giant. Located 90 light years from Earth in the Southern sky constellation Puppis, this planet circles its sun, known as HD70642, every six years.

What is most interesting about this system, though, is what the astronomers didn't find.

Unlike other systems with Jupiter-like planets orbiting at Jupiter-like distances, this system does not have any other gas giants closer to its sun in the region where liquid water could exist - the so-called habitable zone. The finding suggests that this void could be filled by smaller rocky planets.

"If we see a big empty gap," said astronomer Debra A. Fischer, co- author of the Astrophysical Journal article, "we have to wonder if it's really empty."

Our own solar system is "filled up with planets," Fischer said. "If you dropped another planet in, all the other orbits would become chaotic." Because the Jupiter-like planet is in a stable circular orbit it's a good indication that smaller, more Earth-like planets could also be in stable orbits.

The vast majority of the 100 or so extrasolar planets that astronomers have discovered to date are in somewhat chaotic orbits, making it unlikely that a tiny rocky planet could remain in the habitable zone long enough for advanced life forms to evolve. The larger gas giants would most likely kick them out.

The technique that astronomers used to discover this planet, along with the majority of the other planets found over the last decade, will not reveal any "Earths," which would be too small to detect. But it will help astronomers refine their search so, as Carnegie Institution of Washington astronomer Paul Butler said, "perhaps in the next 20 years - within our lifetimes - Earth-like planets might be found."

The method, which Butler pioneered with University of California, Berkeley, astronomer Geoff Marcy, is known as the Doppler Wobble technique. True to its name, this technique detects the slight "wobble" that stars exhibit when their large planets tug on them. The larger the planet, the more the stars wobble, making it much easier to detect huge gas giants than tiny rocky worlds.

"It doesn't seem possible that we can detect Earth-like worlds in Earth-like orbits using ground-based technology," Carter said, referring to the four-meter Anglo-Australian Telescope used to detect the newest extra-solar planet. "What we're doing is laying the groundwork for future missions."

But even though this latest find doesn't give direct evidence that another Earth exists, Carter added: "It improves the chances that there are Earth-like worlds and life out there among the stars."

The National Aeronautics and Space Administration has a trio of spacecraft missions in the works to aid the search for planets like our own: Kepler, the Space Interferometry Mission and the Terrestrial Planet Finder. Kepler, due for launch in 2007, will be the first of the missions to pick up where ground-based telescopes leave off.

Don Brownlee, professor of astronomy at the University of Washington and the co-author of "Rare Earth: Why Complex Life is Uncommon in the Universe," said that the upcoming Kepler mission "will really tell us how common Earth-like planets are around stars similar to the sun."

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