Was this huge delta of the Mars River where its oceans finally disappeared?

For some time, scientists have known that Mars was once a much hotter and wetter environment than it is today. However, there are between 4.2 and 3.7 billion years ago, its atmosphere was slowly eliminated, which turned the surface into a cold and desiccated place that we know today. Even after several missions have confirmed the presence of ancient beds and rivers, there remain unanswered questions about the amount of water in Mars.

One of the most important questions is whether large seas or an ocean have existed in the northern lowlands. According to a new study conducted by an international team of scientists, the ancient river system of Hypanis Valles is actually the remnant of a river delta. The presence of this geological feature indicates that this fluvial system once flown into an ancient Martian sea in the northern hemisphere of Mars.

In the interest of their study, titled "The Delta of Valles Hypanis: the last peak of a sea in early March?" which has recently appeared in the journal Scientific letters of the Earth and planets, the international team consulted data from Mars Reconnaissance Orbiter (MRO) and the 2001 Mars Odyssey probe to study the morphology, sedimentary architecture, and sedimentary environment of the region. Hypanis Valles.

This delta is what separates the southern highlands from the northern lowlands, where an ancient ocean would have existed – a theory that has not yet been proven. Based on the High Resolution Imaging Science Experiment (HiRISE) instrument data and the Odyssey THermal Emission Imaging System (THEMIS) in 2001, the team found evidence convincing that a large expanse of water once covered the northern third of Mars.

As Joel Davis, a postdoctoral researcher at the Group of Planetary Surfaces at the Natural History Museum and co-author of the paper, explains in a recent NHM press release:

"A Martian ocean means that Mars probably has a water cycle very similar to the Earth, with rivers, lakes and now oceans, which probably interacted with the planet. hydrologic about 3.7 billion years ago, and began to close some time later.Our study is not definitive proof for an ocean, but these geological features are very difficult to explain without a . "

Determining whether or not Mars had expanses of water in the past has not been an easy challenge, mainly because Mars does not have the apparent indications of the lakes and oceans on its surface (deposits fine-grained sand or open shoreline). As a result, scientists had to look for other ways to identify where the water was flowing and where the sand was settling, that is, what was going on. say where the sedimentary fans come in.

In this case, the identified fan was a river delta, which forms when a river slows down in the presence of a slower or slower water mass. As a result, all small sediments carried by the river settle on the ground and form geological features (eg, small islands at the mouth of the river) over time. In the past, river deltas were found on Mars, but only in craters where water was flowing into a lake.

For example, the Curiosity rover, which has been studying Gale Crater since landing in 2012, has found ample evidence that the crater was once a lake. This evidence included clay minerals at the base of Mount Sharp, as well as sedimentary deposits and channels found in the crater wall and Mount Sharp, which could only be explained by the waters entering the crater.

Through their study, scientists can now state with certainty that the Hypanis sedimentary blower is evidence of a body of water large enough to be an ocean. Their study also shows how the ocean was removed as the climate became colder and drier. Basically, as the ocean level decreased by nearly 500 meters, the Hypanis Delta began to develop.

Finally, they determined that about 3.6 billion years ago, the water system dried up and disappeared, which is consistent with the time when Mars lost most of its ancient atmosphere. Since then, no water has been able to subsist on the surface except for ice, except for a recently discovered underground lake.

As Dr. Peter Fawdon, Associate Researcher of the Open University and lead author of the study, explains,

"Research has contributed significantly to our understanding of the climate in early March, and we now know that a water cycle similar to the Earth's has become a cold, desert landscape in a relatively short period of time. to gain a better understanding of the number of these river deltas on Mars in order to determine the position and size of its ancient seas. "

This study has not only provided definitive evidence that it is an ocean on Mars, but also that the shoreline of this ancient ocean is close to landing the ExoMars 2020 and March 2020 rovers in the coming years. The fact that an ocean once existed increases the chances that these rovers will find evidence of past Martian life – which is their main goal.

In the last century, our collective understanding of Mars has changed dramatically. Once a planet crossed by canals and populated by little green men, the first robotic missions on the red planet revealed a frozen landscape hostile to life. However, in recent decades, evidence has shown that Mars may have supported life in the past.

And whether life is there or not today, Mars remains a dynamic and fascinating place that can teach us a lot about the history and evolution of our solar system. However, if there are still microbes on the red planet, it is probably the exoMars 2020 and March 2020 that will find them.

Explore more:
A huge lake of liquid water under the south pole of Mars

More information:
Peter Fawdon et al. The delta of Hypanis Valles: the last summit of a sea in early March? Scientific letters of the Earth and planets (2018). DOI: 10.1016 / j.epsl.2018.07.040