Has Hubble found life on Jupiter's largest moon?

NASA scientists believe they may have found signs of life on another world, after the Hubble Space Telescope spotted evidence of a deep reservoir of water on Jupiter's largest moon.

Ganymede, the planet's biggest moon, hides a subterranean ocean thought to hold more water than all of Earth combined.

Scientists have hailed the finding as a "significant milestone", arguing that finding liquid water is one of the key factors in the search for habitable worlds other than Earth, and the search for life as we know it.

Ganymede is slightly larger than Mercury, and is almost 500 million miles from the Sun.

Temperatures are so cold that the water on the surface of the planet freezes as hard as rock - but evidence from Hubble suggests there may be liquid around 100 miles below the crust.

Hubble was used to monitor aurorae above the moon's surface.

The aurorae are tied to the moon's magnetic field, and an ocean lying below the surface would affect the way the magnetic field behaves as it interacts with Jupiter's own enormous magnetic field.

Based on the movement of the aurorae - which is much smaller than it would be if there were no ocean - scientists believe the ocean is around 60 miles deep.

The method was developed by a team based at the University of Cologne in Germany.