A Gigantic Flood Carved Up Mars Not Too Long Ago

Researchers have created new maps of Mars that reveal an ancient network of underground channels, likely formed by a gigantic flood.

The findings were published online Thursday, March 7, in the journal Science.

The discovery was made using a radar instrument on NASA's Mars Reconnaissance Orbiter, a spacecraft that beams back images and other information about Mars.

The Shallow Radar instrument, or SHARD, looks like a long pole that extends out from the spacecraft. It beams sound waves a few hundred feet (and up to 3,000 feet) below the surface of Mars, looking for evidence of liquid or frozen water.

The instrument's antenna detects the frequency of the waves that are returned after bouncing off whatever is beneath the orbiter. These waves will vary with the different densities and composition of the ground — like sand versus water. Because water is good at conducting waves, it will have a stronger radar return, for example.

In this case, the radar tool enabled scientists to reconstruct three-dimensional maps of the biggest underground system of flood channels on Mars. The channels sit in the youngest volcanic region on the planet. Until now, the source, scale and structure of the channels have not been well understood because they are buried by lava flows on the planet's surface.

With the ground-penetrating radar they were able to make out the different layers — the channels and the volcanic rock that is covering it — because of their different makeup.

The 600-mile channel system, known as Marte Vallis, is believed to have been carved out 500 million years ago by a major flood. This is unexpected because Mars is thought to have been cold and dry for the past 2.5 billion years. The channels are also twice as deep as originally estimated.

Researchers have also identified the source of the floodwater — a now-buried series of fractures known as Cerberus Fossae.

The finding tells scientists how water has shaped Mars, including the surface and climate.

The idea that large amounts of water once flowed on Mars — both on the surface and underground — is not new. Giant craters found on the Red Planet's surface suggest that these depressions used to be filled with liquid water, based on the mineral composition of the crater floor.

Finding past evidence of water is important because it is considered a fundamental building block of life — just like carbon or oxygen. Life as we know it could not exist without water.