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Mars may have had an ocean

Elizabeth Howell, News Writer
Jul 18, 2013, 7:00 UTC

Sen—The wet past of the Red Planet may involve quite a bit more water than previously imagined.

New images captured by NASA's Mars Reconnaissance Orbiter reveal evidence of an ancient delta, or sediment deposited by a river, that could have flowed into a Martian ocean.

While not definitive proof, the new images provide compelling evidence that the Martian lowlands in the northern hemisphere were actually the bed of an ocean billions of years ago.

There are other possible clues as well: the hemisphere is very flat, and lower than the southern hemisphere, much like what one would see in Earth's oceans. Following that line of thinking, the border between north and south could have been a Martian coastline.

Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter

Mars and Earth deltas

An ancient delta on Mars (left) compared with a more modern one on Earth. Credit: DiBiase et al./Journal of Geophysical Research/2013 and USGS/NASA Landsat

"In our work and that of others -- including the Curiosity rover -- scientists are finding a rich sedimentary record on Mars that is revealing its past environments, which include rain, flowing water, rivers, deltas, and potentially oceans," stated Mike Lamb, an assistant professor of geology at the California Institute of Technology who co-authored the paper.

"Both the ancient environments on Mars and the planet's sedimentary archive of these environments are turning out to be surprisingly Earth-like."

Mars deltas are becoming a common find on the Red Planet. However, most of these discoveries are in geographic areas that are isolated, such as inside a crater. While water could have flowed inside these areas -- think lakes -- such deltas do not necesssarily provide evidence of greater bodies of water.

Scientists decided to study the hypothetical coastline between the northern and southern hemispheres to see if they could find any evidence of deltas, zeroing in on a 100-square-kilometer area that is in the Aeolis Dorsa region.

The area is known to be covered in features called inverted channels, which are locations where gravel and other materials build up on river bottoms. The larger materials remained behind even after the river and finer, lighter grains evaporated. Aerial views of the region show the channels fanning out, which could suggest several ways they formed.

While an ocean inlet is one possible hypothesis, the researchers noted these could also be evidence of a drainage system that was on a mountain, or that the water was heading in the opposite direction and created an alluvial fan -- a formation where one river channel becomes several smaller ones.

With that being said, in this case scientists noted "an abrupt increase in slope of the sedimentary beds near the downstream end of the channels" -- something often seen on Earth when a stream is going into a much bigger body of water. Unless a surrounding crater or other boundary was present and eroded away over billions of years, it's possible this could be a pointer to a Martian ocean.

The team aims to conduct more observations along the boundary to see if they can find other deltas that could point to more ocean evidence. Results appeared in the July 12 issue of the Journal of Geophysical Research.