Why scientists are so excited about Saturn's icy moon Enceladus
Scientists explain how they discovered a water ocean beneath the ice shell of Saturn's moon Enceladus.
The ocean was revealed after Nasa's Cassini spacecraft spotted plumes of water-ice erupting from fissures at the moon's south pole.
The finding showed that there might be many places in the Solar System where life could get a foothold.
There's more about the Cassini mission in a special Horizon programme on BBC Two which will review the mission on Monday 18 September at 21:00 BST.
14 Sep 2017