The Planet Hunters - Planet OGLE-2005-BLG-390Lb

The smallest and most Earth-like planet outside the Solar System has been discovered and astronomers say it increases the chances of finding extra-terrestrial life. Image right: This artist's illustration shows an icy/rocky planet orbiting a dim star. Astronomers detected an extrasolar planet five times as massive as Earth circling a red dwarf, a relatively cool star.
The distance between the planet, designated OGLE-2005-BLG-390Lb, and its host is about three times greater than that between the Earth and the Sun.
The planet's large orbit and its dim parent star make its likely surface temperature a frigid minus 364 degrees Fahrenheit (minus 220 degrees Celsius).
Credit: NASA, ESA and G. Bacon (STScI) Scientists are excited at the detection of the planet, unromantically named OGLE-2005-BLG-390Lb, because it has a low mass, is rocky and has a thin atmosphere.
With a surface temperature of around -364F (-220C) it is unlikely to support living organisms but researchers believe that the find increases the probability that many other such worlds exist and that some could be suitable for life forms.
OGLE-2005-BLG-390Lb, around five times the mass of Earth and twice its diameter, is more than 20,000 light years away in the constellation Sagittarius, near the centre of our Milky Way galaxy.It is only the third extra-solar planet - one that orbits a star other than the Sun - to be detected using gravitational microlensing, a method that relies on light from a background star being bent and magnified by the gravitational field of a star in the foreground.

Keith Horne, professor of astronomy at St Andrews University, is one of the 73 researchers from 32 institutions who collaborated to make the discovery, which is announced today in the journal Nature.
He said: "Our methods are 50 times more sensitive to the discovery of large gas giant planets, so the fact that the third we found is small and rocky means that there must be a large number of them.
"I expect we will go on finding more small rocky planets. This probably increases the likelihood of the existence of some form of life outside our Solar System."
The new planet orbits a parent star a fifth the size of the Sun. Its surface is thought to be buried deep under frozen oceans.
Gravitational microlensing was first proposed by Einstein. For the effect to work, a star must pass almost directly between the observer and the planet or star being observed. As such events are rare, many distant stars must be continuously monitored to detect planets at a reasonable rate.
Michael Turner, of America's National Science Foundation, said: "This is an important breakthrough in the quest to answer the question, 'Are we alone?'
"The team has discovered the most Earth-like planet yet and demonstrated the power of a new technique that is sensitive to detecting habitable planets. We can now probe a much greater portion of our galaxy."The previous most Earth-like extra-solar planet is GJ 876d, which is 7.5 times the mass of Earth but is too hot to support life.

(Perhaps life as we know it, but extremophiles can and do endure incredible heat.
true masked wabbit)