An ancient alien 'mega flood' has been revealed using 3D scans of the surface of Mars.
Water-carved channels deep beneath the planet's surface show have long suggested that the dry, dusty planet was once saturated with water.
The latest discovery suggests the channels created by one of those floods may be twice as deep as was previously thought.
Above: Nasa's map of Mars reveals areas beneath the Elysium Planitia usually covered by long-cooled lava
This so-called 'mega flood' shaped the planet's surface, carving huge canyons and landmarks.
While the planet has been barren and dry for the last 2.5 billion years, which most of its water frozen at the poles, occasional floods have dramatically altered its surface.
Scientists used the shallow radar onboard Nasa's Mars Reconnaissance Orbiter space craft to scan underneath the Elysium Planitia, an area of Mars which contains one of the largest channels on the planet.
The scan included a 3D picture of Marte Vallis, a 500-mile long system of channels whcih are at least 230 feet deep.
The team at the Smithsonian's National Air and Space Museum said that the source of the floodwater which created the relatively young channels may have originated from a deep reservoir underground, released by volcanic activity.
"Our findings show the scale of erosion that created the channels previously was underestimated and the channel depth was at least twice that of previous approximations," said Gareth Morgan, lead author on the paper.