Scientists say they have discovered a huge frozen sea lying just below the surface of the planet Mars.
Experts have known there is water near the poles of the Red Planet for sometime, but this is the first evidence that water exists elsewhere.
According to Nature magazine the European team think the icy sea, which is about 800 by 900km wide, was formed by a flood five million years ago.
The huge blocks of ice were spotted in images taken by the probe Mars Express.
The space craft has been orbiting the Red Planet since December 2003.
Space expert Jan-Peter Muller said the discovery of the frozen sea is very important: "It's been predicted for a long time that you should find water close to the surface of Mars near the equator.
"But no-one has ever seen a sea before, and certainly no-one has ever seen pack ice before," he added.
Life on Mars hope
The new discovery has made some experts think it's even more likely that life could exist - or at least once existed - on Mars.
Some scientists are now calling for the European Space Agency to send another lander to the planet to find out more.