Scientists from around the globe have discovered evidence of ancient rivers on Mars more than 3.7 billion years old, using high-resolution 3D imaging data.
Sedimentary rocks, found in a 200-metre high Martian rocky cliff, formed by the ancient rivers proves that water was not only present on Mars, but the rivers were probably active for 100,000 years.
This study, published in Nature Communications, adds a new piece to this puzzle, pushing the known timeframe of Martian rivers further back into the past, and providing novel insight into how much water occupied these ancient landscapes.
Dr Matt Balme, Senior Lecturer of The Open University, Dr Francesco Salese and Dr William McMahon from Utrecht University, Netherlands, and Dr Joel Davis, Postdoctoral Researcher at the Natural History Museum, worked alongside a team of international collaborators to make the discovery.
The team of scientists examined high resolution satellite data of the “Izola Mensa” region within the enormous Hellas Impact Crater on Mars, to study the characteristics of the newly discovered sedimentary rocks.
The key observation is that of a 200-metre thick stack of layered rocks visible within the cliff walls. The cross-cutting relationships revealed by the high-resolution data allowed the team to interpret the huge rock outcrop as comprising “fluvial” sedimentary deposits, i.e. formed by sediments deposited by running water.
The team used terrestrial geological field experience to conclude that the cliff face contains stacks of river channels deposits, bounded by distinct horizons which represent periods where erosion dominated the area.
The total time recorded in the continuous parts of the 200-metre-thick succession represents only a fraction of the actual time river processes were likely active in this region. The majority of the stratigraphic record will have either been lost to erosion or is preserved in rocks as of yet undiscovered. Hence it appears that the river processes that formed these rocks occurred over a very long time period.
Dr Matt Balme, Senior Lecturer in the Planetary Environments Research Group at The Open University, said:
“This study shows that rivers were present more than 3.7 billion years ago on Mars, and that they didn’t just erode into the surface, they deposited sediments carried in the flow, built up floodplains, had sandy bottoms, and basically acted just like rivers do on Earth.
The fact these deposits are so old provides more evidence that this ancient period on Mars is the best time period to study if we want to understand whether life ever got started on Mars.”
Dr Joel Davis, a geologist at the Natural History Museum in London, said:
“There are two key differences in this study from previous works. Firstly, the rocks in Hellas are really, really old, possibly even pre-dating the emergence of life on Earth. Secondly, the rivers that formed these rocks weren’t just a “one off” event – they were probably active for tens to hundreds of thousands of years. And we’ve learned this from just one outcrop.”
The technology needed to make these observations comes from NASA’s High-Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter spacecraft, which can take 25cm/pixel resolution images of the Martian surface. For the study, the team used stereo pairs of these high-resolution images to create the high-resolution 3D topography data required.
William McMahon, a geologist at Utrecht University, said:
“Here on Earth, the stratigraphy (i.e. the order and position of sedimentary layers) of sedimentary rocks has been used by geologists for generations to place constraints on what conditions were like on our planet millions or even billions of years ago. Now we have the technology to extend this methodology to another terrestrial planet, Mars, which hosts an ancient sedimentary rock record that extends even further back in time than our own.”
The scale of the preserved river channels seen in the outcrop, and the total thickness of sediment preserved, points to prolonged water discharges consistent with a Martian water-cycle that included precipitation, i.e. rain or snow. This conclusion points to a prolonged presence of water on the surface during Mars’ Noachian period, more than 3.7 billion years ago. This evidence bolsters hope that sedimentary rocks from this period could be the ideal targets for the search for evidence of past life on Mars.
In 2022, the European Space Agency will launch the Rosalind Franklin ExoMars Rover, which will explore Noachian sedimentary terrains looking for evidence of life. Rosalind Franklin will drill down two metres into these sediments and examine the samples for bio-signatures that could point to the presence of past life. Currently, The Open University is working as part of an international team to characterise the landing site for the Rosalind Franklin ExoMars Rover.
For more on the discovery of ancient rivers on Mars read the paper published today in Nature Communications.