Out of more than 6,000 known planets beyond our solar system, astronomers have identified just 45 as the most promising candidates for harbouring life. The catalogue, published in the Monthly Notices of the Royal Astronomical Society on 19 March, is the result of a study led by Professor Lisa Kaltenegger at Cornell University's Carl Sagan Institute. It marks the first systematic attempt to determine which rocky worlds sit within the right conditions for liquid water to exist on their surfaces.