Curiosity Front Hazcam Left B image taken on Sol 2156, August 30, 2018.
Credit: NASA/JPL-Caltech


Now in Sol 2156, the NASA Curiosity Mars rover is on duty.

“After an extremely productive couple of weeks, we are finishing up our work at Stoer!” That’s the report from Abigail Fraeman, a planetary geologist at NASA/JPL in Pasadena, California.

The plan calls for taking quick Chemistry and Camera (ChemCam) and Mastcam observations of the tailings dump pile before packing up and starting the rover’s drive up the ridge towards a next drill location.

Curiosity Mars Hand Lens Imager (MAHLI) photo acquired on Sol 2156, August 30, 2018.
Credit: NASA/JPL-Caltech/MSSS

Sharing a story

“As we leave Stoer, I’d like to take some time to share the story of how and why we came to drill this particular location,” Fraeman explains.

“We first attempted to drill Vera Rubin Ridge back on sol 2112 at the ‘Voyageurs’ target. However, the drill made only a few millimeters of progress into that target before stopping because the rate of downward progress was so slow,” Fraeman adds. “The drill itself performed exactly as it was designed but the Voyageurs rock was simply too hard! It was pretty interesting from a science perspective to see this result, but it also meant we had to work quickly to figure out a plan B.”

The science team agreed, Fraeman continues, that it was scientifically important enough to get a drill sample from the lower part of Vera Rubin Ridge that researchers should try again.

Curiosity Navcam Left B image taken on Sol 2156, August 30, 2018.
Credit: NASA/JPL-Caltech

Think like geologists

But how could they improve their chances of finding a rock that would be softer and easier to drill than Voyageurs? It was time to think like geologists, Fraeman points out.

“In the absence of direct data on rock mechanical properties, we came up with three criteria that we could use to try to find a softer rock. Fraeman reports: (1) Did the bristles of the DRT [Dust Removal Tool] brush leave scratches on the rocks’ surfaces? While not necessarily a direct indicator of what the rock strength would be when we drilled into it, we could at least say rocks that got scratched with the DRT had a softer surface than those that didn’t. (2) How well exposed are the white calcium sulfate veins?”

Curiosity Navcam Left B image taken on Sol 2156, August 30, 2018.
Credit: NASA/JPL-Caltech

Large-scale topography

“On some rock targets, like Stoer, we clearly see veins. On other targets, like Voyageurs, the veins are recessed into the rock,” Fraeman observes. “Recessed veins erode much faster than the surrounding bedrock because the surrounding bedrock is harder. Non-recessed veins tell us the bedrock may be similar in strength to the veins, or, if the veins stick out, the bedrock may be lower in strength.”

Fraeman’s point 3: What does the large-scale topography tell us?

“Broadly, Vera Rubin Ridge is a ridge because it is composed of hard rocks that are more resistant to erosion than their surroundings,” Fraeman notes. “We realized we might use this same logic to find softer rocks within the ridge by trying to drill in local topographic lows or at bases of scarps where the bottom of the scarp is eroding more quickly than the hard rocks on top.”

Curiosity Mastcam Left photo taken on Sol 2155, August 29, 2018.
Credit: NASA/JPL-Caltech/MSSS

Next drill targets

Fraeman says that, fortunately, because Mars researchers had already explored a lot of Vera Rubin Ridge, they already had lots of data in hand to search for next drill targets.

“Several members of the science team put in impressive efforts to quickly go through all of the images we’d taken in the last 200 sols, and we found just a handful of candidates that fit our criteria,” Fraeman reports. “The area near ‘Ailsa Craig’ was close to Voyageurs and looked different enough that we thought it was worth a go. We made more progress drilling into this target than Voyageurs, but still not enough.”

Looking back

“Stoer” was a final choice, and it was initially chosen because it was near the base of a scarp and had more prominently expressed veins.

“We all had a really good feeling about this target.” Fraeman notes, “when we saw the DRT had scratched it, and were thrilled when we saw a successful drill hole. Apparently third time really was the charm for us!”

Looking back on all the drills over the course of the mission, Fraeman says Stoer has got to a favorite spot. “Not only have I been personally wondering about the rocks on Vera Rubin Ridge for six years, but the fact that the science team worked so hard to find this not-so-hard rock makes this particular drill extra sweet.”

Credit: NASA/JPL-Caltech/Univ. of Arizona

Road map

A new Curiosity traverse map through Sol 2156 has been issued by JPL.

The map shows the route driven by NASA’s Mars rover Curiosity through the 2156 Martian day, or sol, of the rover’s mission on Mars (August 30, 2018).

Numbering of the dots along the line indicate the sol number of each drive. North is up. The scale bar is 1 kilometer (~0.62 mile). From Sol 2132 to Sol 2156,

Curiosity had driven a straight line distance of about 127.30 feet (38.80 meters), bringing the rover’s total odometry for the mission to 12.20 miles (19.64 kilometers).

The base image from the map is from the High Resolution Imaging Science Experiment Camera (HiRISE) in NASA’s Mars Reconnaissance Orbiter.

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