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Astronomers Discover Fifth Planet Orbiting Distant Star

By Art Chimes
Washington, DC
07 November 2007

Astronomers Tuesday announced the discovery of another planet orbiting a distant star, making it the most crowded planetary system outside our own. VOA's Art Chimes reports.

More than 260 planets have been identified outside our solar system. The most recently discovered exoplanet, as they're called, orbits a star in the constellation Cancer.

According to Geoff Marcy of the University of California, one of the authors of a new paper announcing the discovery, astronomers already knew the star had four planets.

"We've been observing a sunlike star called 55 Cancri, star 55 in the constellation Cancer, for 19 years, and we watch the wobble of this star as it's yanked on by the planets orbiting it," he said. "And we're just now announcing the discovery of the fifth planet, the first planetary system with five full planets orbiting a sunlike star."

Our solar system has eight planets.

Astronomers estimate the newly-found planet is about 45 times more massive than Earth, and has a year lasting 260 Earth days. Lead author Debra Fischer says the planet may resemble Saturn in some ways.

"This planet, we think, is likely to have a fairly substantial atmosphere," she said. "It's very massive. It might not be the sort of place that, at least life as we know it, would find to be a comfortable environment. However, this planet, in fact, orbits in what we call the habitable zone."

Planets in the habitable zone have a range of temperatures that might support life, if not on the planet itself, then possibly on a moon, if the planet has any moons.

Exoplanets are generally discovered indirectly by detecting changes in the light coming from a star as its orbit is affected by nearby planets. Sometimes it can take years to sort out these Doppler observations.

The more massive the planet, the easier it is to detect. But Debra Fischer, of San Francisco State University, says the growing sophistication of the technique increases the chances of finding planets more like our own.

"So what we're doing right now with our observational technique, the Doppler technique, is taking really the very first steps to finding Earth-like planets. You know, we'll basically give NASA the addresses, the names and addresses, of the most likely candidates for Earth-like planets."

Debra Fischer and her colleagues will publish their findings in an upcoming edition of Astrophysical Journal.

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