Earth-like planet's chilly reception

THE discovery of a planet similar to Earth should happen within the next five years, with the confirmation of alien life forms as little as ten years later, astronomers said yesterday, as they revealed the closest match to our own planet to date.

Scientists at St Andrews University played a leading role in the find, which is being hailed as a breakthrough in the search for extra-terrestrial life.

While it is unlikely to support life - the surface temperature is believed to be -220C - its discovery, announced in the journal Nature, strongly suggests that rocky planets like ours are far more common than lifeless gas giants such as Jupiter.

The planet, designated OGLE-2005-BLG-390Lb, was found using telescopes combined with the gravity of a distant star, which acts like a lens to magnify objects even further away - as predicted by Albert Einstein.

It is about 28,000 light years away and five times as big as the Earth, making it the smallest known planet outside our solar system.

Professor Keith Horne, leader of St Andrews's RoboNet "microlensing" planet search team - one project in an international collaboration involving more than 70 astronomers around the world - said a truly Earth-like planet could be discovered as early as this summer.

He said the astonishing discovery of alien life could come just ten years later, with a search for the main tell-tale sign of living organisms - oxygen in the atmosphere.

"We're very excited about this planet. It's only the third planet we have found with this experimental lensing method. It shows small planets are quite common," Prof Horne told The Scotsman. "Our equipment is 50 times more sensitive to the large planets. That suggests there are 20 to 30 times more little ones than big ones."

He said the discovery of a planet the size of Earth could happen this summer, when observations resumed, but he added: "My best bet would be about 2010."

Prof Horne, one of the world's leading planet-hunters, said it was more difficult to predict when astronomers might find evidence of a planet with life on it.

"The first thing we want to learn is whether habitable planets are common or rare. If they are common, the nearest one is fairly close by," he said. "There are techniques to take pictures of these planets, and from the pictures we can determine whether the planet is alive or not.

"We are looking for signs of pollution caused by living organisms. In our atmosphere, oxygen is 'pollution' caused by plants. That will be the first signature of life. That would probably come about 2020."

The newly-found planet is unlikely to be the site of "first contact" with alien life.

Prof Horne said: "It's freezing. It's like the whole planet is Antarctica. That's because it's far out from its host star, and the host star's temperature is cooler than the Sun."

The planet was not seen directly. Instead its presence was revealed when it passed in front of its star, causing it to "wink".

Dr Martin Dominik, a colleague at St Andrews and co-leader of another planet- hunting team, said: "We saw the usual brightening reaching a peak magnification on 31 July, 2005, after which the event started to fade back symmetrically."

"But on 10 August there was a small 'flash' lasting about half a day. By catching this with two of our telescopes and with careful monitoring, we could conclude that the lens star is accompanied by a low-mass planet."

America designs probe to search for life in Mars ice

NASA plans to search for life in underground ice on Mars by firing a probe that will blast a 30ft crater on the surface of the planet.

The Thor probe - named after the Norse god of thunder but also standing for Tracing Habitability, Organics and Resources - is due to be launched in 2011.

It will be the first time the sub-surface water ice on Mars has been investigated. The idea is to look for water, but also organic compounds such as methane which have been detected in the atmosphere by other missions.

Thor's principal investigator, Phil Christensen, of Arizona State University's Mars Space Flight Facility, said they were adopting a straightforward approach.

"The mission's goal is to expose snow and ice in a previously unexplored part of Mars - the deep subsurface. We'll do this by blowing a crater at least 30ft deep in the Martian ground," he said. "In many areas of Mars's middle latitudes, we see tantalising evidence of dust-covered layers of snow or ice. Thor will aim for this material.

"This unexplored region of Mars may provide chemical and mineral clues to tell us about habitable areas on the planet."