Once, this region of Mars was flooded with a “megaflood”

Thanks to multiple robotic missions that explored Mars’ atmosphere, surface and geology, scientists have concluded that Mars was once a much warmer and more humid place. In addition to having a denser atmosphere, the planet was actually warm enough that running water could exist on the surface in the form of rivers, lakes, and even an ocean that covered much of the Northern Hemisphere.

According to new research based on data collected by NASA Curiosity mission, it appears that the Gale Crater (where the rover has been exploring for the past eight years) suffered massive flooding about 4 billion years ago. These findings indicate that Mars’ mid-latitudes were also covered by water at the same time and offer further clues that the region once supported life.

These findings were the subject of a study that appeared recently in the November 5 issue of Nature Scientific Reports. The responsible research team was led by Dr. Ezat Heydari (professor of physics at Jackson State University) and included several earth scientists, astronomers and researchers from NASA’s Jet Propulsion Laboratory (JPL), Cornell University and the University of Hawaii.

This bottom-up self-portrait of NASA’s Curiosity Mars rover shows the vehicle at the site it came from to drill a rock target called the “Buckskin” on lower Mount Sharp. Credits: NASA / JPL-Caltech / MSSS

On Mars, evidence of the planet’s watery past is written across the landscape in the form of well-preserved geological features. Ironically, it is the nature of the Martian environment today – freezing cold, dry, with no running water and a very rarefied atmosphere – that has allowed this evidence to be preserved over billions of years.

As they indicate in their study, the team analyzed the data obtained from Curiosity on the gravel ridges in the Hummocky Plains Unit and on the ridge and trough band formations in the Striated Unit. These wave-shaped sedimentary deposits are the so-called “megaripples” (aka. Antidunes). As co-author Alberto G. Fairén, a visiting astrobiologist at the College of Arts and Sciences, explained to the Cornell Chronicle:

“We first identified megafloods using detailed sedimentological data observed by the Curiosity rover. The deposits left by the megafloods had not previously been identified with the orbiting data. “

These antidunes at the bottom of the Gale crater measure approximately 9 meters (30 feet) high and are spaced approximately 137 (450 feet) from each other. Furthermore, they are dated to around 4 billion years ago and are identical to the layered sedimentary features on Earth that were deposited by melting ice during the first Quaternary Ice Age (around 2 million years ago).

MRO image of the Gale Crater illustrating the landing site and path of the Curiosity Rover. Credits: NASA / JPL / T. Reyes

Here too, the research team attributes the formation of these characteristics to the melting of ice, likely caused by a large impact that released carbon dioxide and methane from the planet’s frozen reservoirs. The resulting release of water vapor and gases combined to produce a greenhouse effect which led to a temporary increase in temperatures and wetter conditions.

As this water vapor cooled, it condensed to form clouds which led to torrential rains that may have been all over the planet. In the Gale crater, this water accumulated and combined with the waters flowing down from Mount Sharp, located in the center of the crater. The result of all this was a series of flash floods that created mega-cities at the bottom of the crater, which remained intact after the water disappeared.

This latter evidence is yet another indication that the Gale crater once had persistent lakes and streams, as shown by sedimentary deposits. The presence of these long-lived water bodies remains one of the strongest indications that microbial life may have existed in the Gale Crater and Mount Sharp billions of years ago. As Fairén summed up:

“Early Mars was an extremely geologically active planet. The planet had the necessary conditions to support the presence of liquid water on the surface and on Earth, where there is water, there is life. So the first Mars was a habitable planet. Was it inhabited? This is a question that the next Perseverance rover … will help answer. “

Artist’s impression of the Perseverance rover on Mars. Credit: NASA-JPL

On February 18, 2021, the Curiosity rover will be joined by its sister mission, Perseverance. Once he reaches the surface, this robotic explorer will join the search for life on Mars (past and present) and will be the first mission to obtain samples for an eventual return to Earth. Analyzing these will allow scientists to finally get a closer look at Martian soil and rock, which may contain telltale signs of past life.

This mission, and others that will arrive in the coming years, will help pave the way for eventual manned missions to Mars, which will open stores on the Red Planet and attempt to unravel the enduring mysteries about its geological history and evolution.

Further reading: Cornell Chronicle, Nature Scientific Reports

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