Reading rocks to find water on early Mars is an interesting scientific challenge

A 200-metre-high cliff at the edge of one of the largest impact craters in the solar system tells the story of an ancient water landscape. The cliff consists of sedimentary rocks, 3.7 billion years old, formed by rivers that were probably active for more than 100,000 years.

Over the past few decades, thanks to an armada of orbiters, rovers and landers, Mars' early past has been revealed step by step. In particular, morphological, geological and sedimentary clues have been identified and collected, indicating that the planet's surface has been experienced and shaped by large volumes of liquid water flows (rivers). This study adds a new piece to this extraterrestrial puzzle, pushing back the known era of Martian rivers, and providing a new insight into the amount of water that occupied these ancient landscapes.

The study, entitled "Sustained fluvial deposition recorded in Mars' Noachian stratigraphic record", was recently published in Nature Communications. Francesco Salese and an international team of scientists from the United Kingdom, the Netherlands and France, including Véronique Ansan, Senior Lecturer at the University of Nantes, examined high-resolution (25 cm/pixel) HiRISE* orbital data to study the stratigraphic characteristics of recently discovered sedimentary rocks in the north-western region of the Hellas Basin (Izola mensa).

For the first time, the orbital data revealed, through detailed high-resolution architectural analysis, a large outcrop of the Noachian, over 3.7 billion years old, covering an area 1500 m long and 200 m high, and to derive reliable palaeo-environmental interpretations based on sedimentary and stratigraphic evidence.


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 Figure - A. Mars (Mola topography) on which the black arrow indicates the location of the outcrop. B. Daytime thermal infrared image (THEMIS, 100m.pixel-1) showing the regional context: sedimentary plain in which depressions show the sedimentary deposits seen on the 200m high cliff, imaged by the HiRISE camera. C. Three-dimensional view of the mesa showing the location of the outcrop (DTM and HiRISE image). D. Zoom on the architecture of the sedimentary deposits, showing oblique stratifications typical of river environments (HiRISE image, ESP_055357_1540).

The study shows that a fluvial deposit, more than 200m thick, was set up in a hydrological context requiring large amounts of liquid water, perennial and regular over time, about 3.7 billion years ago on the surface of Mars. Such constant flow rivers would require an environment capable of sustaining large volumes of water for long periods of time, and whose hydrological cycle would certainly be controlled by precipitation. Moreover, this sedimentary deposit would demonstrate relatively stable hydrological conditions over more than 100,000 years, adding an additional element to the climatic scenarios of early Mars in favour of the long-time presence of liquid water on the Martian surface.

This type of ancient fluvial sedimentary record is also a potential site preserving the traces of primitive life.

HiRISE (High Resolution Imaging Science Experiment): high resolution visible camera acquiring image with a resolution of 25 cm.pixel-1on board of Mars Reconnaissance Orbiter (MRO) since 2006.


> Reference : Francesco Salese 1,2,6, William J. McMahon1,6, Matthew R. Balme3, Veronique Ansan 4, Joel M. Davis5 &Maarten G. Kleinhans1, Sustained fluvial deposition recorded in Mars’ Noachian stratigraphic record, Nature Communication,
1- Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
2- International Research School of Planetary Sciences, Università Gabriele D’Annunzio,Pescara, Italy.
3- Planetary Environments Group, Open University, Walton Hall, Milton Keynes, UK.
4- Laboratoire de Planétologie et géodynamique, UMR6112 CNRS, Université de Nantes, Université d’Angers, 2 rue de la Houssinère, BP 92208 44322 Nantes cédex 3, France.
5- Department of Earth Sciences, Natural History Museum, Cromwell Road, Kensington, London SW7 5BD, UK

> Contacts : Dr. ANSAN Véronique, email:, Phone: + 33 (0) 2 51 12 54 97