Thursday, January 26, 2006
The new planet was found in the constellation Sagittarius.
SCRIPPS HOWARD
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. But 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.
But the new planet, in the constellation Sagittarius, has about 5-1/2 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 today 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.
Question of life
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.
"This is an important breakthrough in the quest to answer the question 'Are we alone?'" said Michael Turner, assistant director for mathematical and physical sciences at the National Science Foundation, a sponsor of the research.
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.