Thanks to multiple robotic missions that have explored Mars’ atmosphere, surface, and geology, scientists have concluded that Mars was once a much warmer, wetter place. In addition to having a thicker atmosphere, the planet was actually warm enough that flowing 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’s Curiosity mission, it appears that the Gale Crater (where the rover has been exploring for the past eight years) experienced massive flooding roughly 4 billion years ago. These findings indicate that the mid-latitudes of Mars were also covered in water at one time and offers additional hints that the region once supported life.
These findings were the subject of a study that recently appeared in the Nov. 5th issue of Nature Scientific Reports. The research team responsible was led by Dr. Ezat Heydari (professor of physics at Jackson State University) and included multiple earth scientists, astronomers, and researchers from NASA’s Jet Propulsion Laboratory (JPL), Cornell University, and the University of Hawaii.
On Mars, evidence of the planet’s watery past is written all across the landscape in the form of well-preserved geological features. Ironically, it is the nature of the Martian environment today – freezing cold, desiccated, no flowing water, and a very thin atmosphere – that has allowed for this evidence to be preserved over the course of billions of years.
As they indicate in their study, the team analyzed data obtained by Curiosity on the gravel ridges in the Hummocky Plains Unit and the ridge-and-trough band formations in the Striated Unit. These wave-shaped sedimentary deposits are what is known as “megaripples” (aka. antidunes). As co-author Alberto G. Fairén, a visiting astrobiologist in the College of Arts and Sciences, explained to the Cornell Chronicle:
“We identified megafloods for the first time using detailed sedimentological data observed by the rover Curiosity. Deposits left behind by megafloods had not been previously identified with orbiter data.”
These antidunes at the bottom of the Gale Crater measure about 9 meters (30 feet) high and are spaced about 137 (450 feet) apart. In addition, they are dated to about 4 billion years ago and are identical to layered sedimentary features on Earth that were deposited by melting ice during the early Quaternary Ice Age (ca. 2 million years ago).
Here too, the research team attributes the formation of these features to melting ice, which was 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 that led to a temporary rise in temperatures and wetter conditions.
As this water vapor cooled, it condensed to form clouds that led to torrential rain that may have been planetwide. In the Gale Crater, this water pooled and combined with waters flooding down from Mount Sharp, located in the center of the crater. The result of all this was a series of flash floods that created the megaripples at the bottom of the crater, which remained there intact after the water disappeared.
This latest 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 bodies of water remains one of the strongest indications that microbial life could have existed in the Gale Crater and on Mount Sharp billions of years ago. As Fairén summarized:
“Early Mars was an extremely active planet from a geological point of view. The planet had the conditions needed to support the presence of liquid water on the surface – and on Earth, where there’s water, there’s life. So early Mars was a habitable planet. Was it inhabited? That’s a question that the next rover Perseverance … will help to answer.”
On February 18th, 2021, the Curiosity rover will be joined by its sister-mission, Perseverance. Once it reaches the surface, this robotic explorer will join in the search for life on Mars (past and present) and will be the first mission to obtain samples for eventual return to Earth. The analysis of these will allow scientists to finally get an up-close glimpse of Martian soil and rock, which could contain the telltale signs of past life.
This mission, and others that are due to arrive in the coming years, will help pave the way for eventual crewed missions to Mars, which will set up shop on the Red Planet and attempt to unlock the enduring mysteries about its geological history and evolution.