Signs of Earth life are on the Moon
Astronomers have spotted signs of life after pointing the world's largest telescope at the Moon.
But ET has not been hiding next door. The biological fingerprints discovered in moonlight were left by life on Earth.
The scientists were analysing the faint "earthshine" caused by reflected light from the Earth bouncing off the lunar surface.
Encoded within the light waves are tell-tale "biosignatures" - specific combinations of oxygen, ozone, methane and carbon dioxide that betray the presence of organic life.
The researchers also pioneered a super-sensitive method of identifying biosignatures by studying light polarisation.
Similar techniques may in future be used to confirm the existence of life on "exoplanets" orbiting distant stars.
Dr Stefano Bagnulo, one of the astronomers from the Armagh Observatory in Northern Ireland, said: "The light from a distant exoplanet is overwhelmed by the glare of the host star, so it's very difficult to analyse - a bit like trying to study a grain of dust beside a powerful light bulb. But the light reflected by a planet is polarised, while the light from the host star is not. So polarimetric techniques help us to pick out the faint reflected light of an exoplanet from the dazzling starlight."
When light is polarised, its waves have a specific orientation instead of vibrating in all directions.
The new research, published in the journal Nature, was conducted using the Very Large Telescope (VLT), an array of four telescopes on a mountain in Chile that work together. The VLT, which began operating in 1998, is the world's most powerful visible-light telescope.
Using the VLT, the astronomers simulated observing an exoplanet light years away to look for clues about the Earth. Relying purely on the earthshine data, they determined that the Earth's atmosphere is partly cloudy, that part of its surface is covered in oceans, and that vegetation grows on the planet.