A paper published today in the journal Science, and based on data from NASA’s Mars rover Curiosity, describes an ancient system of lakes and streams in Mars’ Gale Crater.
Gale crater is 155 km in diameter and now holds a layered mountain rising about 5 km above the crater floor. This illustration depicts a lake of water partially filling the crater. Image credit: NASA / JPL-Caltech / ASU / UA / Sci-News.com.
While previous theories about this region’s history have been based on observations from afar, on-the-ground data from Curiosity is allowing researchers to directly test the hypothesis that large impact craters were capable of accumulating and storing water for substantial periods of time.
Within Gale Crater, the rover discovered basin surfaces (clinoforms) that could not be observed from orbit.
A large team of planetary researchers from Canada, France and the United States, analyzed sediments along these clinoforms, noting that the basin surface rose with time.
Combining these observations with calculations of the crater’s rim erosion suggests that aggradation – an increase in land elevation caused by the deposition of sediment – occurred.
“Observations from the rover suggest that a series of long-lived streams and lakes existed at some point between 3.8 billion to 3.3 billion years ago, delivering sediment that slowly built up the lower layers of Mount Sharp (more formally known as Aeolis Mons),” said co-author Dr Ashwin Vasavada of NASA’s Jet Propulsion Laboratory.
“However, this series of long-lived lakes is not predicted by existing models of the ancient climate of Mars, which struggle to get temperatures above freezing.”
Erosion of Gale’s northern crater wall and rim generated gravel and sand that were transported southward in shallow streams.
Over time, these stream deposits advanced toward the crater interior, transitioning into finer-grains downstream.
These deltas marked the boundary of an ancient lake where the finest sediments accumulated.
“These finely laminated mudstones are very similar to those we see on Earth,” said co-author Prof. Woody Fischer of the California Institute of Technology in Pasadena, CA.
A view from the Kimberley formation looking south. The strata in the foreground dip towards the base of Mount Sharp, indicating the ancient depression that existed before the larger bulk of the mountain formed. Image credit: NASA / JPL-Caltech.
The analysis suggests that, although water presence was likely transient, ancient individual lakes in this region were stable for 100 to 10,000 years at a time – potentially long enough to support life.
The area traversed thus far by Curiosity would have taken 10,000 years to 10 million years to accumulate, suggesting that the transient lakes were likely sourced throughout time by a common groundwater table.
Furthermore, evidence suggests that over time, wind-driven erosion shifted deposits in the crater to create Aeolis Mons.
These new data provide unparalleled insights into the Mars’ past water patterns, climate and habitability.
“We have tended to think of Mars as being simple,” said lead author Prof. John Grotzinger, also of the California Institute of Technology.
“We once thought of the Earth as being simple, too. But the more you look into it, questions come up because you’re beginning to fathom the real complexity of what we see on Mars.”
“This is a good time to go back to reevaluate all our assumptions. Something is missing somewhere,” he concluded.
_____
J.P. Grotzinger et al. 2015. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars. Science, vol. 350, no. 6257; doi: 10.1126/science.aac7575
