Astronomers Discover Two Midsized Planets ; the Find Moves Scientists `Step Closer' to Discovering Other Earths, Leader Says
Posted on: Saturday, 4 September 2004, 06:00 CDT
Two American teams yesterday announced the discovery of two midsized planets, a find that puts astronomers on the brink of locating other Earths.
"It puts us a step closer. We can't quite see the Earth-like planets yet, but we're seeing their big brothers," said one of the discoverers, Paul Butler of the Carnegie Institute of Washington.
One planet surprisingly circles the 3 billion-year-old dim star Gliese 436 about 30 light-years away from our solar system. Older stars of this type are among the most numerous in the galaxy but were not thought to have planets.
A light-year is the distance light travels in a year in space, about 6 trillion miles.
The second planet orbits 55 Cancri, a star much like our own some 41 light-years away. Cancri has three gassy giant planets circling it, giving scientists a chance to study diversity in extrasolar systems.
"This star is the premier lab for study of the formation and evolution of planetary systems," said another of the astronomers, Barbara McArthur of the University of Texas at Austin.
"This is a milestone. We've crossed a hurdle" from the Jovian gas giants to smaller planets such as Neptune and Earth, added Butler.
The two planets, some of the smallest yet to be found outside our solar system, are about the heft of Neptune.
Neptune's mass, 17 times that of Earth, is much smaller than most of the 135 extrasolar gargantuans discovered so far. Most of those planets are gaseous giants hundreds of times bulkier than compact Earth and unlikely to nurture life.
For the past decade, astronomers have raced to find new terrestrial territory. In the next decade, the planet hunters will have new space observatories from NASA to refine their quest for habitable worlds.
The planets were uncovered using a technique that detects the gravitational tug of the planet on the nearby star. The tug is very slight, so larger planets and their greater pull are easier to find than small worlds.
News from the American teams followed word from Swiss scientists of another Neptune-sized planet about 50 light-years away.
Taken together, the findings suggest that the Milky Way may be thick with planets of all types.
"The more we learn, the more it appears that planets are very common, and that they come in a wide range of sizes and orbits," said astronomer Ted Bunn of the University of Richmond. "Solar systems like ours, with small rocky planets, may well be very common."
University of Virginia astronomer Steve Balbus predicted that the Milky Way will reveal Earth-like planets in the next five years.
"This discovery marks the penultimate step before we begin to find Earth-like planets in orbit around other stars," said astronomer Ken Wilson of the Science Museum of Virginia.
The discoveries were led by McArthur and Butler and Geoff Marcy of the University of California at Berkeley, who used one of the twin Keck telescopes in Hawaii.
The findings by both teams were peer-reviewed and will be published in the Astrophysical Journal.
On the Internet
JET PROPULSION LABORATORY: http://planetquest.jpl.nasa.gov/ index.html
PLANET SEARCH: http://exoplanets.org/
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