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A small, rocky planet orbiting a small, dull star may be the most Earth-like world yet discovered outside the solar system, according to a team of European astronomers. The planet is at the right distance from its star for liquid water, so it’s possible that oceans cover part of its surface.

Artist’s concept of Gliese 581’s possible watery planet. (ESO)

The planet orbits Gliese 581, a red-dwarf star that is 20.5 light-years away. The small, cool star emits only about 1 to 2 percent as much energy as the Sun. Using a telescope at the European Southern Observatory in Chile, astronomers discovered the planet by measuring its minute gravitational pull on the star. They calculate that its diameter is about 1.5 times that of Earth, or roughly 12,000 miles.

The planet orbits the star once every 13 days, at a distance of less than seven million miles — far closer than Earth is to the Sun. At that distance, the planet’s average temperature is above freezing, so it could be a comfortable abode for life.

However, scientists won’t know more about the planet’s habitability until new spacecraft that are designed to measure the composition of planets in other star systems enter orbit in the coming years.