(Reuters) - It remains in the realm of science fiction for now but the discovery of a new planet just four light years away will reignite a race to find a twin of planet Earth that may host extraterrestrial life.
The step change comes as the most powerful telescopes ever built are about to enter into service and as ideas about where life could exist are being turned on their head. At the same time, scientific discussion about the possible existence of alien life is becoming more mainstream.
"I think scientists are very happy having a rational conversation about the likelihood of life out there," said Bob Nichol, an astronomer at Portsmouth University in Britain.
Nichol said this was partly driven by the discovery of new planets such as one identified this week in the Alpha Centauri star system, the closest yet outside our solar system.
Over 800 of these so-called exoplanets have been discovered since the early 1990s.
"An explosion in the number of planets makes it so much more likely," said Nichol, adding that the many formats in which life appears on Earth is indirect evidence, though not proof, that life is out there.
Researchers from the Geneva Observatory said the newest planet to be found was too close to its own sun to support life. But previous studies have suggested that when one planet is discovered orbiting a sun there are usually others in the same system.
Rival astronomers are now likely to start scouring Alpha Centauri for more planets, possibly in the habitable zone around its stars.
NEW EYES AND EARS
The technological eyes and ears that scientists have at their disposal are about to take a leap forward too, broadening and deepening their search.
Barring a surprise discovery of microbes on Mars, we will see alien life long before we are ever able to touch it.
"I think it is realistic to expect to be able to infer within a few decades whether a planet like Earth has oxygen/ozone in its atmosphere, and if it is covered with vegetation," Martin Rees, Britain's Astronomer Royal, told Reuters.
The next decade will see two record-breaking telescopes come on line; the Square Kilometre Array (SKA), a huge radio telescope sited in South Africa and Australia, and Europe's Extremely Large Telescope (E-ELT) that will sit on a mountain top in Chile's Atacama desert and be the largest optical telescope ever built.
Their main task will be to probe the origins and nature of galaxies, but they will also look for signs of life on planets that can now only be seen in the roughest detail.
"I think the capabilities of new telescopes means that the detection of an ETI (extraterrestrial intelligence) is more likely in the next few decades, than it was in the last," said Mike Garrett, general director of Astron, the Netherlands Institute for Radio Astronomy.
With a mirror almost 40 meters in diameter, The E-ELT will be able to reveal planets orbiting other stars and will produce images that are 16 times sharper than the Hubble Space Telescope.
When completed in 2024, the SKA radio scope will comprise 3,000 dishes, each 15 meters (50 feet) wide, together with many more antennae that together will be able to see 10 times further into the universe and detect signals that are 10 times older.
Among those signals could be radiation given off by military radar from the nearest million or so stars. "So," said Nichol, "if there are advanced civilizations on planets around those stars, we could see them".
Isobel Hook, an Oxford University astrophysicist who is working on the E-ELT, said the new telescope will boost the search for life elsewhere.
"The ELT should also allow us to study the atmospheres of extra-solar planets and look for ‘bio-markers' such as water, carbon dioxide and oxygen molecules in their spectra," she said.
With the right equipment, Hook said the ELT may be able to use spectroscopy, the study of the particular wavelengths of light reflected by an object, to detect signs of vegetation on distant planets.
The search for alien life has long been framed by the dogma of a ‘goldilocks zone' around faraway suns that is just the right temperature - neither too hot nor too cold - to allow liquid water, essential for life as we know it.
That theory is now being challenged, expanding the potential area in which life could exist.
Other sources of heat have been identified and scientists have come up with radically new ideas about the forms life could take after studying organisms that live in some of the most inhospitable places on Earth.
Earlier this year, Xavier Bonﬁls of the Institute of Planetology and Astrophysics in Grenoble estimated there could be tens of billions of rocky planets in our galaxy alone with the right temperature to support life.
Meanwhile, researchers at Aberdeen University in Scotland are working on a computer model which suggests astronomers should sharply increase the number of planets they regard as capable of hosting life.
Although scientists would expect water on the surface of a planet outside a habitable zone to be frozen, researcher Sean McMahon has argued the heat generated from inside a planet could be enough for large underground reservoirs of liquid water.
The study of pockets of life on Earth in places not dissimilar to an area being probed on Mars by NASA's rover Curiosity has also altered conventional wisdom.
A team from Centro de Astrobiología in Madrid led by Felipe Gomez studied organisms in the sun-baked Chott el Jerid salt pan in Tunisia, the acidic Rio Tinto in Southern Spain and the permafrost on Deception Island in Antarctica.
Another team from North Carolina State University recently published research on a single-celled organism that lives in a hot spring near Mount Vesuvius in Italy and is able to eat uranium and draw energy from it.
The research suggests that planets hostile to human life might nevertheless suit these so-called extremophiles, leading to what Duncan Forgan at the Royal Observatory in Edinburgh calls "a much more complicated and richer concept of the habitable zone."
But at roughly 100,000 light years across, the universe is a big place and even if there is intelligent life elsewhere sending out signals astronomers say the chances of not hearing them are still considerable.
(Editing by Andrew Osborn)