Curiosity finds historical ripples on Mars

NASA's Curiosity rover has been exploring Mars since 2012 and recently found evidence of ice-free ancient ponds and lakes on the surface. The rover found small ripples like those seen in sandy lake beds on Earth. They would have been formed by wind-driven water moving back and forth across the surface. The inescapable conclusion is that the water would have been exposed to the elements rather than covered by ice. The discovery suggests that the waves formed 3.7 billion years ago.

Mars is the fourth planet in our solar system and the second smallest of all large planets. It is known for its vibrant red color, which is caused by iron oxide in the surface material. Classified as a terrestrial planet, Mars resembles Earth in many ways, with valleys, volcanoes and even evidence of dry riverbeds. The similarities end there, however, with the polar ice caps, which consist largely of carbon dioxide ice, an atmosphere that is unbreathable, and a surface that is cold and dry. It has always held a particular fascination for us, largely due to vague hints over the centuries of extraterrestrial intelligence, but more recently that it may once have been habitable.

A full disk view of Mars, courtesy of VMC. Photo credit: ESA

One such rover exploring the Martian landscape is the Curiosity Rover, sent by NASA in 2011. It arrived on Mars in August 2012 and has been exploring the region around Gale Crater ever since. Curiosity's main goal is to study the climate and geology and assess whether they might have supported the life of indigenous people in the past. To achieve this goal, it is equipped with a range of instruments, from drills for collecting soil samples to cameras and instruments for analyzing atmospheric samples.

New simulations are helping the Curiosity rover's ongoing sampling campaign. Image credit: NASA/JPL-Caltech/MSSS

A recent paper published in the journal Science Advances by John Grotzinger, Harold Brown Professor of Geology at Caltech, and Michael Lamb, Professor of Geology, shared their findings. They found two sets of seemingly ancient ripples on the surface of Mars, thought to be dry bodies of water with ripples preserved in the rock. The waves are tiny waves and are commonly observed on beaches and lake beds on Earth as wind-driven water flows over the shallows. The team is particularly pleased that the water was not frozen and was once exposed to the elements as a liquid.

The waves discovered by Curiosity in Gale Crater are the strongest evidence yet that liquid water existed in the history of the Red Planet. Analysis of the rocks and waves suggests that they were formed 3.7 billion years ago. It is believed that Mars' atmosphere and climate must have been much warmer than today and more dense. Tight enough to carry liquid water outdoors.

NASA's Curiosity rover continues to search for signs that conditions in Mars' Gale Crater may support microbial life. Image credit: NASA/JPL-Caltech/MSSS.

The team was able to create computer models from the waves they found to try to determine the size of the lake. The size of the waves and the distance can be used to determine how much water was present. The wave height of 6 mm and the spacing of 4 to 5 cm suggest that the lake was shallow, possibly even less than 2 meters deep. One of the wave groups, known as Prow Outcrop, was found in an area that once consisted of wind-blown dunes. The other set was found nearby in the sulfate-bearing Amapari Marker Band. The two regions come from slightly different times, showing us that the warm, dense atmosphere occurred at multiple times or at least over a long period of time.

The discovery was a tremendous help to paleoclimate studies on Mars, which attempted to map the changing conditions on Mars. NASA's Opportunity Rover was the first mission to detect waves on the surface, but the nature of the waters was uncertain. This latest discovery has provided a fascinating glimpse into early conditions on Mars, with bodies of liquid potentially scattered across the landscape. Further research is needed to determine how frequently the waves occur.

Source: Signatures of ice-free ancient ponds and lakes on Mars

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