the thin crescent Moon setting over ESO’s Paranal Observatory in Chile

Astronomers looking at Earthshine reflected from the moon have concluded that there is life on Earth!  This technique can help in the search for Extraterrestrial life.

The image above shows the thin crescent Moon setting over ESO’s Paranal Observatory in Chile. Credit: ESO/B. Tafreshi/TWAN

By observing the Moon using ESO’s Very Large Telescope, astronomers have found evidence of life in the Universe — on Earth. Finding life on our home planet may sound like a trivial observation, but the novel approach of an international team may lead to future discoveries of life elsewhere in the Universe. The work is described in a paper to appear in the 1 March 2012 issue of the journal Nature.

We used a trick called earthshine observation to look at the Earth as if it were an exoplanet,” says Michael Sterzik (ESO), lead author of the paper. “The Sun shines on the Earth and this light is reflected back to the surface of the Moon. The lunar surface acts as a giant mirror and reflects the Earth’s light back to us — and this is what we have observed with the VLT.

The astronomers analyse the faint earthshine light to look for indicators, such as certain combinations of gases in the Earth’s atmosphere, that are the telltale signs of organic life. This method establishes the Earth as a benchmark for the future search for life on planets beyond our Solar System.

The fingerprints of life, or biosignatures, are hard to find with conventional methods, but the team has pioneered a new approach that is more sensitive. Rather than just looking at how bright the reflected light is in different colours, they also look at the polarisation of the light, an approach called spectropolarimetry. By applying this technique to earthshine observed with the VLT, the biosignatures in the reflected light from Earth show up very strongly.

Co-author of the study Stefano Bagnulo (Armagh Observatory, Northern Ireland, United Kingdom) explains the advantages: “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.

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