Curiosity Drills Into Mars and Strikes Clay

"Aberlady," the section of exposed bedrock in Mount Sharp's "Clay-bearing Unit" that the Curiosity rover drilled a sample of on April 6, 2019. The drilling operation pulled up a section of the rock, shown by the fresh raised cracks surrounding the drill hole site.  (NASA/JPL-Caltech/MSSS)

While prospecting the slopes of Mount Sharp for evidence of Mars' past watery climates, NASA's Curiosity rover struck clay.

If this doesn't sound as worthy of a "Eureka!" as hitting the golden mother-lode, consider that, to scientists studying Mars' past climates, clay is as good as gold.

Mosaic of the "clay-bearing unit" that NASA's Curiosity rover arrived at in February. The edge of Vera Rubin Ridge, Curiosity's previous exploration site, can be seen at the top of the picture.
Mosaic of the "clay-bearing unit" that NASA's Curiosity rover arrived at in February. The edge of Vera Rubin Ridge, Curiosity's previous exploration site, can be seen at the top of the picture. (NASA/JPL-Caltech/MSSS)

Clay is a treasure to researchers because the minerals it contains are known to have formed in the presence of water.  So, analyzing Martian clays is a means of exploring what role water has played in Mars' past climates. Mars' once wetter, possibly more Earth-like, and maybe even life-friendly environment has long since dried up, but clues to it persist in the rocks.

Curiosity drilled the April 6 clay sample from a patch of exposed bedrock, nicknamed "Aberlady," within a region of Mount Sharp called the "clay-bearing unit."

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The Saga of Mars' History Written in Stone

Mount Sharp is a 3-mile-high mound of sedimentary rock sitting in the middle of 90-mile-wide Gale Crater, which we know once contained deep lakes that repeatedly formed and dried up in cycles.

The sediments were laid down at different times in the past two billion years, and each layer represents a page in the climate history of Mars. Erosion by wind action has opened up these pages for Curiosity to read.

Curiosity's Quest for Water

Mount Sharp's "clay-bearing unit" was discovered from orbit by NASA's Mars Reconnaissance Orbiter in the years prior to Curiosity's 2012 landing. That detection is one of the main reasons that Gale Crater, and particularly Mount Sharp, were chosen for Curiosity's expedition.

Curiosity can bore into hard rock to get samples, with a hammering rock drill on its long robotic arm. The drill's jack-hammer action was needed to penetrate earlier hard mudstones, but the April 6 clay tasting was of soft rock and required only rotary action.

The drilled rock samples are delivered by the robotic arm to Curiosity's internal laboratory instruments for analysis.

Curiosity started detecting clay minerals in mudstone samples shortly after landing, discoveries that only continued along its uphill trail. These lower mudstones are believed to have formed when rivers carrying sediments flowed into ancient lakes, where the sediments settled out on the lake bottom near the inlet.

Fine sediment layers along Mount Sharp's lower slopes typical of lake bottom sediments deposited by the waters of river inflow. Picture taken in 2014 by the Curiosity rover.
Fine sediment layers along Mount Sharp's lower slopes typical of lake bottom sediments deposited by the waters of river inflow. Picture taken in 2014 by the Curiosity rover.

While scientists await results of Curiosity's analysis of the Aberlady sample, they are surveying the unexplored territory surrounding the rover — maybe like kids in a candy shop. Several intriguing geological features beckon with promises of discovery. There's a lot to look forward to.

Curiosity's Progress and Future

With all the recent headlines grabbed by new and upcoming Mars missions — InSight and the Mars 2020 rover namely — plus 2018's loss of the veteran Opportunity rover, Curiosity's dogged and determined uphill progress may have been overshadowed by these robots of past, present, and future.

But, Curiosity weathered last year's major global dust storm without a hitch — the same dust storm that ended Opportunity's 15-year Martian marathon. Indeed, Curiosity has fed us regular reports of mineralogical paleo-water-sightings for many months now, making the truly remarkable findings almost a routine event.

Google Earth image showing Curiosity's 2012 landing site and its present location in the Clay-Bearing Unit above Vera Rubin Ridge. The summit of Mount Sharp is at the upper right, and the distant rim of Gale Crater is shown in the background.
Google Earth image showing Curiosity's 2012 landing site and its present location in the Clay-Bearing Unit above Vera Rubin Ridge. The summit of Mount Sharp is at the upper right, and the distant rim of Gale Crater is shown in the background. (NASA/Google Earth)

But with this new rung of Mount Sharp's sedimentary ladder now climbed, Curiosity's progress up the 3-mile-high mountain can be appreciated. Though it has only climbed a vertical distance of about 1,000 feet in seven years, and in the bigger picture is still much closer to Mount Sharp's foot than its summit, no other interplanetary rover in history can come close to boasting such a mountain-climbing record.

What will Curiosity encounter in this new phase of is exploration, and how much higher will it climb before it joins Opportunity in the history books?

More to come.

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