ABORTED DRILL ATTEMPT AT VOYAGEURS
Curiosity attempted drilling into the top of Vera Rubin ridge at a site named Voyageurs on sol 2112 (16 July 2018). This Mastcam image, taken the next sol, shows that the drill barely penetrated at all, even using the drill's highest permitted percussion setting.
The drill barely penetrated. After only 3.7 millimeters, forward progress stopped. No sample.
With their enthusiasm dampened, but not their determination, the team commanded the rover to drive away from the very brightest hematite signal to a spot they thought might have softer rocks. Ailsa Craig, attempted on sol 2122, wasn’t any softer; it achieved only a couple more millimeters of depth, and it still was not deep enough to get any sample into the drill (the drill has to penetrate at least 15 millimeters into the rock for that). They drove away two sols later.
Drill attempt at Ailsa Craig
NASA / JPL / MSSS
DRILL ATTEMPT AT AILSA CRAIG
Curiosity attempted to drill at a site named Ailsa Craig, on Vera Rubin ridge, on sol 2122. The drill only penetrated a few millimeters, not deep enough to acquire a sample.
The failed drill attempts weren’t entirely useless. Both resulted in small piles of freshly ground rock powder. The APXS and ChemCam teams are very happy to target such fresh surfaces for elemental chemistry analysis, because even a small amount of scraping penetrates beneath the surface coating of dust and weathering rind that can obscure rock composition.
Searching for softer rocks
Clearly, it would save a lot of effort (not to mention precious mission resources) if the team could figure out ahead of time which rocks are going to be drillable, and which aren’t. The question comes down to how hard the rock is.
Those of you who have taken an Earth science class have probably heard of the Mohs hardness scale for minerals, but Mohs is not the scale that’s used for rock hardness. Rocks are composed of mineral grains. Mohs hardness (measured from 1 to 10, with talc being softest and diamond being hardest) refers to how resistant those grains are to being scratched -- a harder mineral scratches a crystal of a softer mineral. But the Mohs scale doesn’t say anything about how resistant the grains are to being broken apart. A block of solid talc will support more weight, and be harder to drill into, than a pile of teeny diamonds held together with honey.
To talk about rock hardness, geologists refer to its compressive strength. Curiosity’s drill is a percussion drill, so what matters is how resistant its grains are to being powdered by its percussive hammering. What clues might the Curiosity team use to figure out whether a rock will have low enough compressive strength for drilling to work, other than actually trying to drill it?
One possible clue comes from the rover’s brush, which has steel bristles. When the rover brushes a rock -- as it does almost every time it puts the APXS compositional instrument on a rock target -- the steel bristles of the brush sometimes scratch the rock surface. If the brush scratches the surface, the rock is probably on the soft side and an easy drill target. However, not scratching doesn’t necessarily mean it’s not drillable. And of course this scratch test requires the rover to actually reach out and touch its arm to a rock, which is costly in terms of mission time and resources.
One clue that Curiosity can see from a distance is veins. Veins are everywhere in Gale’s rocks. Most of the time, erosion leaves veins standing out from the rock surface, indicating that the rocks are less resistant to erosion than the veins. In some places on Vera Rubin ridge -- notably, at both Voyageurs and Ailsa Craig (see the photos above) -- the veins are places that are eroded into the rocks, indicating that the rocks are more resistant. So Curiosity needs to look for places where the veins stand out, or at least aren’t eroded away.
A third clue -- one that can even be spotted from orbit -- is in the geomorphology. You find harder rocks capping topography (which is why it’s no surprise the top of Vera Rubin ridge is made of especially hard rock; it's the highest topography around). If you see a break in slope -- a place where there is a steep scarp capping a shallow slope -- then you know that natural forces have had an easier time eroding the rock that makes the shallow slope than the rock that makes the steep scarp. So, all else being equal, the team might select drill targets in flatter rocks that they find at the toes of scarps.
Phil Stooke's Curiosity Route Map: Vera Rubin ridge drilling traverse, sols 2053-2132
NASA / JPL / UA / Phil Stooke
PHIL STOOKE'S CURIOSITY ROUTE MAP: VERA RUBIN RIDGE DRILLING TRAVERSE, SOLS 2053-2132
Success at Stoer
The team had picked Voyageurs and Ailsa Craig based on orbital chemistry (the hematite signal). When that didn’t work out, they drove to a spot near where they had seen veins standing out and where they found a flattish place at the base of a scarp. It wasn't as bright a spot from orbit, but the measurements from ChemCam and APXS were "within the in situ-derived chemical family" of the Pettegrove Point rocks they were trying to sample -- good enough. Once they got there, they used the brush, and scratched the rock. Then they tried drilling a third time. That’s how they succeeded at Stoer.
Curiosity pulled up to Stoer on sol 2132, and achieved the full commanded drill depth, 46 millimeters (of a commanded 45) on sol 2136. Delivery to CheMin happened on sol 2141, and to SAM on sol 2147. SAM decided not to take a second sample, and they dumped and cleaned the drill on sol 2154 and drove away on sol 2156. Pretty quick work!
Successful drill at Stoer, Curiosity sol 2136
NASA / JPL / MSSS
SUCCESSFUL DRILL AT STOER, CURIOSITY SOL 2136
It took multiple attempts, but the Curiosity team finally found a soft enough spot for drilling atop Vera Rubin ridge at Stoer on sol 2136 (9 August 2018). The drill penetrated 46 millimeters into the rock, deep enough to acquire plenty of sample powder.
If you look at the hematite map at the top of this post, though, Stoer lies in rocks that look a bit more like Duluth than the ridge top rocks from orbit. Did Stoer have the chemistry what they wanted to find? Did the Curiosity team actually learn something about the rocks that made the strong hematite signal visible from space? Alas, I can’t tell you. My blog updates focus on operational details because that’s what the mission shares in real time. Science takes longer, because it takes time to reduce data and place it into context and it’s normal for scientists to reach the wrong conclusions before they reach the right ones (or, at least less wrong ones). Scientists do their best not to share the likely-to-be-wrong early speculations publicly. I’m eagerly awaiting the first scientific presentations on the drilling campaign across Vera Rubin ridge.
If you’re keeping score at home, you might notice the commanded drill depths are decreasing over time. Before the feed anomaly, they routinely drilled to 65 millimeters. At Duluth, they commanded 50 millimeters. At Stoer, it was 45. I wouldn’t be surprised to see the next drill site commanded to a depth of only 40. They’re drilling less deep just to save wear on the drill, especially the percussion mechanism. Once the drill has penetrated into the ground to a depth of 20 millimeters, any further drilling won’t get more material to deliver to the instruments, it just contributes to the size of the eventual dump pile. They do want to have some material available to make a dump pile. The dump pile is what they analyze with the chemistry instruments, APXS and ChemCam. So they’ll always drill to whatever depth past 20 gets them a satisfactory dump pile.
The next drill site will be a spot where they can compare and contrast the “blue” and “red” rock types of the upper ridge (see this earlier Vera Rubin ridge post for some discussion of what those color names mean).
Curiosity attempted drilling into the top of Vera Rubin ridge at a site named Voyageurs on sol 2112 (16 July 2018). This Mastcam image, taken the next sol, shows that the drill barely penetrated at all, even using the drill's highest permitted percussion setting.
The drill barely penetrated. After only 3.7 millimeters, forward progress stopped. No sample.
With their enthusiasm dampened, but not their determination, the team commanded the rover to drive away from the very brightest hematite signal to a spot they thought might have softer rocks. Ailsa Craig, attempted on sol 2122, wasn’t any softer; it achieved only a couple more millimeters of depth, and it still was not deep enough to get any sample into the drill (the drill has to penetrate at least 15 millimeters into the rock for that). They drove away two sols later.
Drill attempt at Ailsa Craig
NASA / JPL / MSSS
DRILL ATTEMPT AT AILSA CRAIG
Curiosity attempted to drill at a site named Ailsa Craig, on Vera Rubin ridge, on sol 2122. The drill only penetrated a few millimeters, not deep enough to acquire a sample.
The failed drill attempts weren’t entirely useless. Both resulted in small piles of freshly ground rock powder. The APXS and ChemCam teams are very happy to target such fresh surfaces for elemental chemistry analysis, because even a small amount of scraping penetrates beneath the surface coating of dust and weathering rind that can obscure rock composition.
Searching for softer rocks
Clearly, it would save a lot of effort (not to mention precious mission resources) if the team could figure out ahead of time which rocks are going to be drillable, and which aren’t. The question comes down to how hard the rock is.
Those of you who have taken an Earth science class have probably heard of the Mohs hardness scale for minerals, but Mohs is not the scale that’s used for rock hardness. Rocks are composed of mineral grains. Mohs hardness (measured from 1 to 10, with talc being softest and diamond being hardest) refers to how resistant those grains are to being scratched -- a harder mineral scratches a crystal of a softer mineral. But the Mohs scale doesn’t say anything about how resistant the grains are to being broken apart. A block of solid talc will support more weight, and be harder to drill into, than a pile of teeny diamonds held together with honey.
To talk about rock hardness, geologists refer to its compressive strength. Curiosity’s drill is a percussion drill, so what matters is how resistant its grains are to being powdered by its percussive hammering. What clues might the Curiosity team use to figure out whether a rock will have low enough compressive strength for drilling to work, other than actually trying to drill it?
One possible clue comes from the rover’s brush, which has steel bristles. When the rover brushes a rock -- as it does almost every time it puts the APXS compositional instrument on a rock target -- the steel bristles of the brush sometimes scratch the rock surface. If the brush scratches the surface, the rock is probably on the soft side and an easy drill target. However, not scratching doesn’t necessarily mean it’s not drillable. And of course this scratch test requires the rover to actually reach out and touch its arm to a rock, which is costly in terms of mission time and resources.
One clue that Curiosity can see from a distance is veins. Veins are everywhere in Gale’s rocks. Most of the time, erosion leaves veins standing out from the rock surface, indicating that the rocks are less resistant to erosion than the veins. In some places on Vera Rubin ridge -- notably, at both Voyageurs and Ailsa Craig (see the photos above) -- the veins are places that are eroded into the rocks, indicating that the rocks are more resistant. So Curiosity needs to look for places where the veins stand out, or at least aren’t eroded away.
A third clue -- one that can even be spotted from orbit -- is in the geomorphology. You find harder rocks capping topography (which is why it’s no surprise the top of Vera Rubin ridge is made of especially hard rock; it's the highest topography around). If you see a break in slope -- a place where there is a steep scarp capping a shallow slope -- then you know that natural forces have had an easier time eroding the rock that makes the shallow slope than the rock that makes the steep scarp. So, all else being equal, the team might select drill targets in flatter rocks that they find at the toes of scarps.
Phil Stooke's Curiosity Route Map: Vera Rubin ridge drilling traverse, sols 2053-2132
NASA / JPL / UA / Phil Stooke
PHIL STOOKE'S CURIOSITY ROUTE MAP: VERA RUBIN RIDGE DRILLING TRAVERSE, SOLS 2053-2132
Success at Stoer
The team had picked Voyageurs and Ailsa Craig based on orbital chemistry (the hematite signal). When that didn’t work out, they drove to a spot near where they had seen veins standing out and where they found a flattish place at the base of a scarp. It wasn't as bright a spot from orbit, but the measurements from ChemCam and APXS were "within the in situ-derived chemical family" of the Pettegrove Point rocks they were trying to sample -- good enough. Once they got there, they used the brush, and scratched the rock. Then they tried drilling a third time. That’s how they succeeded at Stoer.
Curiosity pulled up to Stoer on sol 2132, and achieved the full commanded drill depth, 46 millimeters (of a commanded 45) on sol 2136. Delivery to CheMin happened on sol 2141, and to SAM on sol 2147. SAM decided not to take a second sample, and they dumped and cleaned the drill on sol 2154 and drove away on sol 2156. Pretty quick work!
Successful drill at Stoer, Curiosity sol 2136
NASA / JPL / MSSS
SUCCESSFUL DRILL AT STOER, CURIOSITY SOL 2136
It took multiple attempts, but the Curiosity team finally found a soft enough spot for drilling atop Vera Rubin ridge at Stoer on sol 2136 (9 August 2018). The drill penetrated 46 millimeters into the rock, deep enough to acquire plenty of sample powder.
If you look at the hematite map at the top of this post, though, Stoer lies in rocks that look a bit more like Duluth than the ridge top rocks from orbit. Did Stoer have the chemistry what they wanted to find? Did the Curiosity team actually learn something about the rocks that made the strong hematite signal visible from space? Alas, I can’t tell you. My blog updates focus on operational details because that’s what the mission shares in real time. Science takes longer, because it takes time to reduce data and place it into context and it’s normal for scientists to reach the wrong conclusions before they reach the right ones (or, at least less wrong ones). Scientists do their best not to share the likely-to-be-wrong early speculations publicly. I’m eagerly awaiting the first scientific presentations on the drilling campaign across Vera Rubin ridge.
If you’re keeping score at home, you might notice the commanded drill depths are decreasing over time. Before the feed anomaly, they routinely drilled to 65 millimeters. At Duluth, they commanded 50 millimeters. At Stoer, it was 45. I wouldn’t be surprised to see the next drill site commanded to a depth of only 40. They’re drilling less deep just to save wear on the drill, especially the percussion mechanism. Once the drill has penetrated into the ground to a depth of 20 millimeters, any further drilling won’t get more material to deliver to the instruments, it just contributes to the size of the eventual dump pile. They do want to have some material available to make a dump pile. The dump pile is what they analyze with the chemistry instruments, APXS and ChemCam. So they’ll always drill to whatever depth past 20 gets them a satisfactory dump pile.
The next drill site will be a spot where they can compare and contrast the “blue” and “red” rock types of the upper ridge (see this earlier Vera Rubin ridge post for some discussion of what those color names mean).
Curiosity update, sols 2093-2162: Three tries to successful drill atop Vera Rubin Ridge-- 2
![Curiosity update, sols 2093-2162: Three tries to successful drill atop Vera Rubin Ridge-- 2]()
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on
October 15, 2018
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