Traces of ancient rivers in the Aeolis Dorsa region on Mars

Traces of the ancient rivers of Aeolis Dorsa (Image courtesy Cardenas et al)
Traces of the ancient rivers of Aeolis Dorsa (Image courtesy Cardenas et al)

An article published in the journal “GSA Bulletin” describes a research on the region of the planet Mars called Aeolis Dorsa. Benjamin T. Cardenas and other colleagues from the Jackson School of Geosciences at the University of Texas at Austin used images captured by space probes to determine the presence of traces of rivers that existed about 3.5 billion years ago. That region contains some of the most spectacular and dense river deposits on Mars.

Aeolis Dorsa is a region that is part of the Aeolis quadrangle, as well as two craters where two NASA rovers landed: Spirit in Gusev crater and Curiosity in Gale crater. The Aeolis Dorsa sedimentary basin has already been the subject of research for the presence of traces of ancient rivers, for example the one described in an article published in the magazine “Icarus” in June 2015.

Today, it’s possible to see the sedimentary deposits that formed during the Esperian period, between 3.7 and 3 billion years ago, with current surfaces exposed to erosion during that period up to the beginning of the next one, the Amazonian. That thanks to the process called topographic inversion, where the deposits that once filled the rivers are exhumed in such a way that now has ridges above Mars surface.

Using high resolution images and topographic data from NASA’s Mars Reconnaissance Orbiter and Mars Global Surveyor that are orbiting Mars, the researchers identified the traces of these river deposits but also changes in the sedimentation styles controlled by changes in the coasts. They also developed a method to measure the direction of the paleo-transport direction for a part of those ridges.

In particular, some of the most exposed sedimentary deposits are present in the Medusae Fossae Formation of Aeolis Dorsa. The Medusae Fossae stretch over 5,000 kilometers (more than 3,000 miles) along Mars equator and for this reason are split into various quadrangles.

The researchers found in the sediment traces similarities between the scale of multiple episodes of rise and decline in the water level of Aeolis Dorsa’s rivers and those of sea level changes on Earth. In both cases, over the course of time there were differences of over 50 meters and this suggests a long-term stability, not catastrophic hydrological events such as floods.

These cycles on Mars are consistent with the presence in ancient times of a large lake, a sea or even an ocean with fluctuations in water levels. That’s not surprising considering the results of other researches on the geology and climate that existed on Mars over 3 billion years ago when the red planet was similar to Earth.

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