British scientists say they will lead a $650 million program searching for chemical signs of life on planets orbiting distant stars.

Researchers at University College London are at the head of the Exoplanet Characterization Observatory mission, backed by the European Space Agency, that will use a new space telescope to look for biomarkers in the atmospheres of exoplanets, The Independent reported Monday.

They will search for molecules of chemicals that may indicate the presence of life, they say.

"One of the key aims of our mission is to see if we can detect molecules such as ozone and carbon dioxide in the atmospheres of planets not much bigger than Earth," head UCL researcher Giovanni Tinetti said.

"These molecules are key biomarkers -- signs that life might be, or might have been, present."

The EChO mission will focus on Earth-sized planets in the "habitable zone" of Sun-like stars, also known as the "Goldilocks zone, the region where conditions are not too hot and not too cold but "just right" to allow the existence of liquid surface water.

The EChO space telescope is scheduled to be launched between 2020 and 2022.

ESA's decision to back the mission follows discoveries made NASA's Kepler space telescope.

Earlier this month, Kepler scientists announced a new tally of 1,235 planet "candidates" orbiting stars beyond the Sun, including 54 potential "habitable zone" planets, five of which were Earth-sized.