In April 2007, astronomers announced the discovery of the most Earth-like planet so far found outside our Solar System. This planet is not much bigger than the Earth. It orbits the faint star Gliese 581, which is 20.5 light-years away in the constellation Libra. The mean temperature of this ‘'super-Earth' is between 0 and 40 degrees Celsius, which means that any water there could exist in liquid form.

Its radius is estimated at only 1.5 times the Earth's radius, and models predict that the planet could be either rocky, or covered with oceans. It will become the prime target for telescopes in space that can discern the tell-tale light signs of biological processes. The orbiting observatories would look for trace atmospheric gases like methane, or signs of chlorophyll, essential to plant life on Earth. See: ‘'Red Edge / Earth Shine'.