Evidence for Tsunamis in an Ancient Martian Ocean and the Search for Habitable Environments

shoreline stand and Tsunami deposites

By Ginny Gulick, Senior Research Scientist

Early in its geological history, Mars was thought to have experienced massive outpourings of ground water that erupted from beneath an ice-rich permafrost, carving the enormous flood channels still seen today and inundating large regions of the northern plains to form an ocean.

However, a problem with this hypothesis has been the lack of identifiable and unambiguous paleo-shoreline features.

Using geomorphic and thermal image mapping combined with numerical modeling, a recent study published in Scientific Reports shows evidence for two mega-tsunami events that happened approximately 3.4 billion years ago.  These produced widespread, landward facing flow deposits and associated backwash channels extending for tens to hundreds of kilometers into the cratered highlands.

“We were surprised to find that the older and younger tsunami deposits look so different,” said lead author J. Alexis P. Rodriguez, who is a senior research scientist at the Planetary Science Institute in Tucson, Arizona. “The older tsunami washed ashore and deposited enormous volumes of debris, and evidence for the water hurtling back into the ocean is represented in widespread ‘backwash.’”

“We think that after the ocean shoreline receded to a lower elevation – which likely took place during a period of extreme climatic cooling lasting several million years – the younger tsunami occurred.  Enormous waves froze as they washed over the frigid Martian landscape, before they had a chance to flow back into the ocean,” Rodriguez said.

“The tsunami deposits likely contain rocks and sediments from the ocean floor that were picked up and transported landward by these very large waves,” noted Virginia Gulick, a SETI Institute senior research scientist and a co-author on the paper. “Tsunami deposits are similar to flood deposits, except that they’re moving in the reverse (landward) direction.”

The researchers believe that, in comparison to the extremely cold and dry surface thought to have characterized Mars at the time, the ocean floor is more likely to have included habitable environments. In addition, the long amplitude and wavelength of a tsunami wave could transport marine material landward from several hundred meters in depth. Therefore, exploring tsunami deposits on Mars would allow sampling of a variety of potential ecosystems from a pre-existing ocean.

“On Earth, tsunami deposits contain a significant mud or fine-grained component.  On Mars, this finer-grained component could have preserved physical or chemical evidence of past microbial activity, if it existed,” said Gulick. “If there were habitable environments, then biosignatures could have also been preserved in the large boulders visible in the older flow deposits.”

The research was conducted using visible and thermal images, combined with digital topography from Mars Odyssey, the Mars Reconnaissance Orbiter (MRO), and the Mars Global Surveyor. The research team was supported by the NASA Postdoctoral Program, NASA’s Planetary Geology and Geophysics Program, NASA’s MRO HiRISE, and the NASA Astrobiology Institute. 

Read More: http://www.nature.com/articles/srep25106

 


Virginia Gulick
Senior Research Scientist

Wielding degrees in geoscience, Ginny Gulick examines erosional features on Mars, looking for the tell-tale signs of running water. Some of the meandering valley networks that lace the martian landscape may be proof of a warmer, wetter world, one that existed billions of years ago. But other features, including gullies found around many impact craters and valley walls, may bespeak water that’s still erupting and flowing on the martian surface today.

These clues as to where there was, and still may be, water on the Red Planet deserve more careful scrutiny, and Ginny is part of the HiRISE (High Resolution Imaging Science Experiment) team that directs the high resolution camera on the Mars Reconnaissance Orbiter, now busy snapping pictures of this alien landscape. It’s important to choose which parts of Mars will be photographed, as the MRO will only be able to image about 1% of the total surface.

In addition to these research efforts, Ginny is heavily into education. She has led the development of a web-based, image target suggestion tool which will allow anyone (especially students) to offer their opinions as to which martian features should be photographed with the MRO, and then allow them to collaborate in the analysis of the photos. Studying gullies is one way to avoid a research rut. More Info.