As I wrote this post, the Sun set on Curiosity's 562nd sol on Mars. When I last checked in with Curiosity, the rover had driven westward down Moonlight and Violet valleys, and I wrote about how the mission's new strategy of keeping to sand-filled valleys would provide some really nice views of geology in the valley walls. Curiosity proved that right away, grabbing some fine mosaics of pretty rocks in the middle of the very long sol 548 drive. This spot is called "Scrutons":
And this 3D view shows "Junda" in the foreground, with Mount Sharp in the background. Junda was the first really good look Curiosity got at the so-called "striated terrain" that crops out in lots of places in this particular region. It's beautifully layered, and those layers are tilted. I'll have more to say about that below, when I talk about another outcrop called Kylie.
Before I get going into the details, here's a nice route map covering the region discussed in this post.
As usual, I'm peppering this post with some brief updates from scientist Ken Herkenhoff, via the USGS Astrogeology website.
The Sol 549 drive brought the rover close enough to the outcrop dubbed Bungle Bungle to allow MAHLI and APXS measurements, so the Sol 550 plan focuses on contact science. First, ChemCam will zap and image the outcrop, then the arm will be deployed. After the contact science has completed, the rover will drive about 22 meters to get a better view of the path ahead.
Bungle Bungle is such a beautiful outcrop. If you don't enlarge any of the other images in this post, make sure to click through twice to enlarge this one to its full 7544-pixel-wide glory. It seems to be made of lots of large chunks of other rocks of a variety of sizes. Those chunks are slightly rounded but not what I'd call "round." The variety of sizes and incomplete roundness tell you that these chunks weren't transported very far from wherever they originated. The roundness tells you that there was some water involved. We see lots of rocks that look like this in the mountains around Los Angeles. Those Los Angeles rocks formed from underwater slumps or slides of material being shed off of the rapidly rising mountains, and the mountains' rapid rise continued to lift those rocks above the water where we can see them today. There probably weren't tectonic (mountain-building) forces like that operating in Gale crater, though, so we'll need another explanation for how these rocks formed. We are probably looking at just one or a few sediment deposition events, where a brief flood of water quickly shoved a whole lot of sediment around, dumping a bunch of poorly sorted stuff in the spot we see here.
Here is the view ahead into the north-south segment of valleys that Curiosity turned into after finishing up at Bungle Bungle. She was parked on the saddle between Violet Valley and the valley containing the Kylie outcrop. The layered stuff in the middle ground is Kylie.
They took a long drive into that valley on sol 552 that put them immediately north of Kylie, and another long drive on sol 553, which placed them to the west of Kylie. Here are two Mastcam views from those drives. I have stretched the heck out of the color in these two panoramas, trying to discern differences among the rocks in the outcrops. First, the sol 552 view, from the north:
Next, a view combining images from after the sol 553 drive and before the sol 554 drive, from the west:
The "striated terrain" that you can see in HiRISE images is clearly made up of some kind of finely laminated rock whose layers are slightly tilted. On Earth, a common reason for tilted layers is layers that formed flat and were tilted as a result of tectonics. On Mars, that's a less likely scenario; it's better to ask how you can form layers that were tilted in the first place. There are two main ways to do that on Earth. One way is to blow sand around with wind, which makes cross-beds. We've seen those on Mars a lot, especially at Opportunity's landing site. But there's another, potentially more interesting way to make fine-grained tilted layers: in a delta, where a river containing fine sediment reaches a lake and drops its load. The delta builds outward in tilted beds in a way that looks superficially similar to windblown sand. I don't know which one we're looking at here. If forced to guess, I'd guess we're looking at windblown sands, but I would love to be wrong and find out we're looking at a delta deposit, because that is a particularly excellent kind of depositional environment to trap and preserve organic material.
There had been discussion of Kylie as a possible surrogate for the kind of science they are planning to do at the outcrops at Kimberley, but it appears that they decided that Kimberley was superior, so they kept right on moving, with a wheel-imaging drive on sol 554 and then another long drive on sol 555 that blasted past Kylie for good, keeping them on the road toward Kimberley.
I have been traveling this week to a meeting of the HiRISE (the big camera that has been taking images of rovers from orbit, science team, so am catching up with what MSL has been up to. Drive progress has been good, requiring some discipline on the part of the MSL science team to resist diverting the rover toward interesting outcrops. In addition, the SAM instrument has been doing overnight combustion experiments that require lots of power. The last one of these is planned early in the morning of Sol 558, so there are no daytime activities planned for Sol 557. Later on Sol 558, Mastcam and ChemCam observations of a target dubbed "Mount Amy" are planned, followed by MAHLI and APXS observations of a soil target named "Johnny Cake." The rover will then drive about 60 meters on Sol 559 and take the standard post-drive images to prepare for possible contact science on Sol 560.
Here is a picture of the terrain ahead of the rover after the sol 559 drive. We're looking in the direction that Curiosity had planned to be driving, over a little rise down into a valley that would give them a nearly straight shot at Kimberley. Unfortunately, this terrain doesn't look nice at all. It's not pointy bedrock, like the kind that chewed up Curiosity's wheels before they got to Dingo Gap, but there are a lot of big rocks lying around. It looks like the Pathfinder landing site. And I don't like the fact that the horizon is so close; we'd have to drive up and into this rocky field just to see the terrain ahead.
It's been a while since I traveled to JPL to serve as SOWG Chair for MSL planning, so I decided to spend a few days in Pasadena this week. I'm glad I did, because it would have been much more difficult to get the job done this morning from Flagstaff. Several options were "on the table" including contact science, a full set of MAHLI wheel images, targeted remote sensing, and a couple of drive direction choices. So the science team had to prepare contingency plans for these varied scenarios and react to updates from the engineering team regarding the risk of the rover slipping in response to arm motions and potential drive hazards. Once the rover state and nearby terrain were evaluated, we settled on contact science followed by a drive toward the west, and the rest of the planning day went very smoothly. The Sol 560 plan includes APXS and MAHLI observations of a rock dubbed "Secure" followed by a ~27-meter drive.
Instead of driving straight through this rocky stuff, Curiosity detoured to the west (right), around it. You can see how the sol 560 drive skirted the edge of that extremely rocky terrain.
Here's a funny tweet from one of the rover drivers, Matt Heverly, about this kind of terrain:
At the beginning of tactical operations this morning, the plan for Sol 561 was to take a set of MAHLI wheel images. But the nearby terrain was not ideal for wheel imaging, and a safe path ahead was visible, so we decided to drive toward the west again. This didn't leave much power for other activities, but we were able to squeeze in a few, including a CheMin vibration activity in preparation for the next sample ingestion/analysis.
Here's the view after sol 561:
Just right of center in that panorama is what looks like a nice little valley for driving. Curiosity will drive toward that area, but not go very far in that direction; she needs to take a sharp left turn, south, in order to move toward Kimberley. We can't quite see Kimberley from here, yet; there are a couple of rises that block the view. It looks just a bit rocky going down into the next valley. I wonder if they'll drive backwards on sol 563. They did a wheel survey on sol 562, and are planning sol 563 today; according to rover driver Matt Robinson, it'll be a drive and arm-work sol.
To me it doesn't look likely that they will quite make it to Kimberley before the next big milestone on the mission: the annual Lunar and Planetary Science Conference, a meeting of planetary geologists that runs from March 17 to 21. There is not a special session specifically devoted to Curiosity at LPSC, but there will undoubtedly be a press briefing and there'll be lots of talks spread over several oral and poster sessions, which I will, of course, be attending. Stay tuned for that!