from bbc.co.uk: Astronomers have estimated how many of the 100 billion stars in our galaxy hosts a potentially habitable planet. Using data from Nasa’s Kepler space telescope, they argue that one in five stars like the Sun hosts an Earth-sized world located in the “habitable zone“. This zone is the region around a star where temperatures allow for water – a key ingredient for life – to stay liquid at the surface. The researchers have published details in the journal PNAS.