Curiosity rover confirms ancient Martian lake

View from Yellowknife Bay in Gale crater, looking west-northwest. This area of sedimentary deposits is now known to be the former bottom of a freshwater lake. Photo Credit: NASA/JPL-Caltech

Paul Scott Anderson

Some exciting new results from the Curiosity rover mission on Mars were announced yesterday at this year’s American Geophysical Union meeting in San Francisco. Basically, as previously suspected, Curiosity landed in an ancient lakebed inside Gale crater, and those habitable conditions apparently lasted for a longer time than previously thought.

Curiosity had already confirmed that a fast-moving river or stream once ran through the landing area, leaving behind gravel deposits just like those found on Earth. The water cut through the eroding crater wall and collected inside the crater. Just how much water there was in total in Gale crater isn’t known yet, but now Curiosity has confirmed that there was at least one long lake covering part of the crater bottom, including where the rover landed and is still traveling now.

The lake was similar to long narrow lakes on Earth called “finger lakes” and fed from the water which emptied into the crater. Not only that, but analysis by the rover of mudstone on the former lake bottom showed that it was a freshwater lake, not too acidic or salty. It was probably a cold lake according to the analysis, but it was certainly a very habitable environment. From the press release:

“Not only has Curiosity accomplished its primary goal of finding evidence for an ancient environment that could have supported life, but it also has provided evidence habitable conditions existed more recently than expected and likely persisted for millions of years.”

The implications are that such habitable conditions lasted longer than previously thought. As Curiosity project scientist John Grotzinger explains:

“This habitable environment existed later than many people thought there would be one. This has global implications. It’s from a time when there were deltas, alluvial fans and other signs of surface water at many places on Mars, but those were considered too young, or too short-lived, to have formed clay minerals. The thinking was, if they had clay minerals, those must have washed in from older deposits. Now, we know the clay minerals could be produced later, and that gives us many locations that may have had habitable environments, too.”

Mineral analysis of sedimentary rocks at the Yellowknife Bay location near the landing site revealed smectite, a type of clay mineral. According to David Vaniman of the Planetary Science Institute in Tucson, Ariz.:

“Smectite is the typical clay mineral in lake deposits. It is commonly called a swelling clay – the kind that sticks to your boot when you step in it. You find biologically rich environments where you find smectites on Earth.”

This was also the first time ever that a rock sample on Mars had been dated from analysis of its mineral content in-situ; that is, while it still sat in place on the surface of the planet instead of being examined in a laboratory on Earth such as for Martian meteorites or Moon rocks brought back by Apollo. The drilled sample, from the Cumberland rock outcrop, is estimated to be between 3.86 billion and 4.56 billion years old.

While the rocks themselves are that old, other analysis indicated that they have been exposed on the surface for only about 60-100 million years. The mudstone is gradually being weathered and exposed by abrasion from wind-blown sand.

Finding such exposures of more recently exposed rocks will also help scientists in their search for preserved organic material in the rocks. Now, the best place to look seems to be at the base of retreating scarps (steep or near vertical cliffs or escarpments), on the downwind side, similar to where Curiosity was before in Yellowknife Bay. Drilling in these areas offers the best chance to find organics which haven’t been destroyed yet by cosmic rays hitting the surface. Curiosity’s previous drillings so far were not in such locations and yielded very low detection of organics. But that is how we learn, and science advances, from repeated experimentation and analysis over time. As it happens, another good scarp location is coming up along the rover’s drive path, which Curiosity should reach in a couple of months.

The related science abstracts and papers are available here

This article was first published on Examiner.com

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