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Scientists Spot Earth-Like Planet Near Core of Milky Way

Posted on: Monday, 30 January 2006, 06:00 CST

By Lee Bowman

An icy, probably rocky ball detected near the Milky Way's center by an international network of telescopes is the most Earth-like planet yet found outside our solar system, scientists say.

Astronomers have recorded more than 150 planets beyond our neighborhood in the last decade or so. All of them are Jupiter- sized or larger (Jupiter has the mass of 317 Earths) -- so large that their gravitational pull causes the stars they orbit to wobble, giving their existence away to human observers.

The new planet, in the constellation Sagittarius, has about 5 times the mass of Earth and a relatively cool parent star that it circles about every 10 Earth years, according to a report on the discovery published Thursday in the journal Nature. Also, the scientists report, the planet's distance from its sun is more than three times what Earth's is from its sun.

"This planet is actually the first and only planet that has been discovered so far that is in agreement with the theories for how our solar system formed," said Uffe Grae Jorgensen, an astronomer with the Niels Bohr Institute in Copenhagen, Denmark, and a member of the discovery team.

Researchers don't think the planet can sustain life, given that it has an estimated surface temperature of minus-364 degrees Fahrenheit, about the same as Pluto's. While it may have a thin atmosphere, the planet's rocky surface is probably covered with deep frozen oceans.

More than 73 scientists from 32 institutions took part in the study. For many of the researchers, the most exciting result was proving that their search technique, called gravitational microlensing, could find such a small planet. Scientists presumably will be able to find objects closer in size to Earth and orbiting in "habitable zones" around stars where temperatures could potentially sustain liquid water on their surfaces.

"With this method, we let the gravity of a dim, intervening star act as a giant natural telescope for us, magnifying a more distant star, which then temporarily looks brighter," said Andrew Williams of the Perth Observatory in Australia, one of the observing stations.

"A small 'defect' in the brightening reveals the existence of a planet around the (intervening) lens star. We don't see the planet, or even the star that it's orbiting; we just see the effect of their gravity."

The planet's gravitational pull bends light rays from the distant star and magnifies them like a lens. By analyzing the brightening of the distant star's light rays, researchers can identify and estimate the size of objects passing in front of it.

Each giant planet discovered so far was detected by observing a wobble in a star caused by the gravitational effects of the respective planet.

Source: Cincinnati Post

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