Caltech Scientists Discover Evidence of Ancient Ocean on Mars

NASA's Mars rover Curiosity has already discovered evidence of water on Mars, including the presence of flowing rivers that may have coursed across the red landscape. Yet there has been little evidence to support larger bodies of water, such as oceans. Now, though, scientists at Caltech have discovered evidence for an ancient delta on the Red Planet where a river may have once emptied into a vast ocean.

In order to learn a little bit more about the surface of Mars, researchers used new high-resolution images from the Mars Reconnaissance Orbiter (MRO) in order to study a 100-square-kilometer area. Previous images have shown that this area is covered in ridge-like features of inverted channels, but researchers weren't sure exactly how these channels may have formed. With the newest images, they were able to get a closer look at the formations.

"Scientists have long hypothesized that the northern lowlands of Mars are a dried-up ocean bottom, but no one yet has found the smoking gun," said Mike Lamb, a coauthor of the paper, in a news release.

In the images, these channels appear to fan out, which hints at three possible origins. They could have once been a drainage systems in which streams flowed down a mountain and converged to form a larger river, they could have once flowed in the other direction and formed an alluvial fan, or the channels are actually part of a delta, which emptied into a large body of water such as an ocean.

In order to find out which of these scenarios was most plausible, the researchers analyzed data from images taken by the HiRISE camera at different points in orbit. They then examined the statigraphic layers of the inverted channels, piecing together how sediment might have been deposited along the ancient rivers. In the end, they found which way the water flowed in the channels, suggesting that they were looking at the remains of an alluvial fan or a delta. They then narrowed down their findings further; they discovered an abrupt increase in slope of the sedimentary beds near the downstream end of the channels. This meant that the most likely scenario was a delta rather than an alluvial fan.

"This is probably one of the most convincing pieces of evidence of a delta in an unconfined region-and a delta points to the existence of a large body of water in the northern hemisphere of Mars," said Roman DiBiase, one of the authors of the new paper, in an interview with Discovery News.

The findings could be huge for understanding the history of Mars. If an ocean did exist in the planet's ancient past, it's very possible that it once may have harbored life. In addition, the findings could allow scientists to better target areas for future exploration.

The findings are published in the Journal of Geophysical Research.