Nasa has unveiled an amazing simulation of the wet, warm planet that Mars used to be - before it all went wrong.

The artists' impressions video captures the look and feel of the planet, with rolling white clouds and lakes of liquid water on the surface.

Mars today has no liquid water on the surface, due to low atmospheric pressure and its cold temperature.

But around four billion years ago it was a different story. Nasa's probes on the surface have so far turned up evidence for a world rich with the conditions in which life could emerge.