Alien-hunters have developed a powerful new tool to discover life on other worlds. It works by checking a distant planet’s atmosphere for the “fingerprints” of ET.

an impression of sunlight shining through the Earth's atmosphere as seen from the MoonAstronomers tested it by using the Moon as a mirror during a total lunar eclipse to reflect back sunlight that had passed through the Earth’s own atmosphere.

A giant UK telescope in the Canary Islands was used in the experiment – which provided even more powerful evidence of life on Earth than the scientists expected.

They say it vastly improves our chances of finding alien life outside the solar system. It comes hot on the heels of news that US scientists have devised a way to detect oceans of water on planets outside the solar system.

The test was carried out during a total lunar eclipse because that is when the only light we see from the Moon is sunlight that has been scattered onto it through our own atmosphere.

The light carries vital data about the chemistry of our own planet in what is called a transmission spectrum. Astronomers say they will observe similar spectra when an alien planet passes in front of its parent star and the starlight shines through that planet’s atmosphere.

The experiment, using the UK’s William Herschel Telescope and neighbouring Nordic Optical Telescope on La Palma, is reported in this week’s issue of Nature.

Enric Palle, lead author of the paper, from the Instituto de Astrofisica de Canarias, said: “Now we know what the transmission spectrum of a inhabited planet looks like, we have a much better idea of how to find and recognize Earth-like planets outside our solar system where life may be thriving.

“The information in this spectrum shows us that this is a very effective way to gather information about the biological processes that may be taking place on a planet.”

Pilar Montañes-Rodriguez, from the Instituto de Astrofisica de Canarias, added, “Many discoveries of Earth-size planets are expected in the next decades and some will orbit in the habitable zone of their parent stars.

“Obtaining their atmospheric properties will be highly challenging; the greatest reward will happen when one of those planets shows a spectrum like that of our Earth.”

More than 300 planets have been found orbiting other stars in the last 15 years and astronomers expect to find more resembling Earth soon using space telescopes and improved techniques on the ground.

Picture: An artist’s impression of sunlight shining through the Earth’s atmosphere as seen from the Moon. (Credit: Gabriel Perez Diaz, SMM, Instituto de Astrofisica de Canarias).