Post by Sowelu on Jan 26, 2006 8:17:41 GMT -5
Earth's twin found at heart of Milky Way
Marilyn Head
ABC Science Online
Thursday, 26 January 2006
Astronomers have discovered the most Earth-like planet so far, close to the centre of our galaxy.
The international team says the planet's relatively small size and large orbit imply a rocky-icy composition with a thin atmosphere.
The discovery, involving a global network of telescopes and reported in today's issue of the journal Nature, is good news for astronomers searching for planets outside our solar system that may support life.
"This discovery is a strong hint that these lower-mass objects are very common," says lead author Dr Jean-Philippe Beaulieu from the Institut d'Astrophysique de Paris.
The discovery of OGLE-2005-BLG-390Lb also backs current theoretical models of planetary formation, the scientists say.
These models predict finding planets the size of Earth to Neptune orbiting red dwarf stars, small cool stars, between one and 10 times the distance from the Earth to our Sun.
The new planet has mass more than five times that of Earth and orbits a red dwarf at more than two-and-a-half times the distance between the Earth and the Sun.
This makes it the first relatively small extrasolar planet discovered not huddled close to its parent star.
The planet is about 28,000 light years away, near the centre of the Milky Way, and was discovered using a technique astronomers say is better at finding smaller planets.
Hunting for extrasolar planets
Most extrasolar planets discovered have been 'hot Jupiters' or gas giant planets in small orbits, detected by the gravitational 'wobble' they induce in the parent star.
"That technique is sensitive to massive planets orbiting nearby stars. But the microlensing method ... can detect much smaller planets orbiting at larger distances around distant stars," says New Zealand's Dr Michael Albrow from the University of Canterbury.
Albrow is a founding member of the PLANET collaboration, which found the planet, one of the three microlensing collaborations involved from 32 institutions in 12 countries.
Dr Andrew Williams from Australia's Perth Observatory explains how microlensing works.
"The gravity of a dim intervening star acts as a giant natural telescope, magnifying a more distant star, which brightens temporarily. A small 'defect' in the brightening reveals the existence of a planet around the lens star."
Because the chances of exact alignment are very rare, astronomers continuously monitor dense star fields such as the galactic centre, which is best seen from the southern hemisphere.
The Japanese-New Zealand Microlensing Observations in Astrophysics group supplied extra data.
The group happened to be testing the world's largest dedicated microlensing telescope at the time, a 1.8 metre telescope at Mount John University Observatory in Tekapo, New Zealand.
abc.net.au/science/news/stories/s1554907.htm
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