When we last left our hero, on sol 569, Curiosity had just spotted her next science stop, a place called Kimberley. Kimberley is easy to spot in orbital images: three conical mounds at its corners are organized in a way that looks like the holes on a bowling ball. Those mounds are the topmost of three types of rock exposed at Kimberley. Below it is a smooth unit, and below that, something called the "striated unit." From orbit, you can see the striated unit all over this area; appears stripey, with the stripes generally oriented east-west. Curiosity photographed it at Kylie. As I write, it's sol 584; with long-ish drives on sols 572 and 574 and a short bump on sol 581, Curiosity has now driven up to the northern edge of Kimberley and is doing some arm work at the outcrop of the striated unit.
Next they will drive the rover around the northeastern mound and up and onto the striated unit, where they plan to drill, acquiring the first rock sample since Cumberland on sol 279, ten months ago now. They had some problems on sols 576 and 578 with arm activities they were doing to prepare for the Kimberley drilling campaign. There's nothing wrong with the rover and they're back to normal operations now, but the problems did cost them most of a week's worth of activity. The cloud has a silver lining; the delay gave scientists more time to check out the amazing outcrop that's sitting in front of them. They're wrapping up some arm work there and should hit the road again this weekend.
Here's a detailed report on the activities of the last two weeks. As usual I'm folding in Ken Herkenhoff's informative updates, which he posts on the USGS website.
Sol 571 - 573 Update On Curiosity From USGS Scientist Ken Herkenhoff: APXS the Observation Tray (17 March 2014)
We had the option to perform contact science on Sol 571, but there were not compelling targets within the arm's reach, so an APXS integration on the observation tray was substituted. It had been over a year since such a measurement, which will be useful as a baseline before another sample is dumped onto the tray. I was supporting ChemCam planning for the weekend plan, focusing on fitting an RMI calibration activity into the plan, but the rover orientation was not ideal for this observation and we decided not to include it. The rover will drive again on Sol 572, followed by untargeted remote science on Sol 573.
Here's the photo of the observation tray. Compare it to this one, taken on sol 70. It's convenient that the wind cleans off the tray between sample inspections! There's just a light coating of dust over everything, as is always the case on Mars.
On sol 571 they also shot a 360-degree panorama that's particularly beautiful for its low light. You can see the full panorama here; I like Damia's "postcard" version, below.
To return to Ken's updates:
Sol 574 Update On Curiosity From USGS Scientist Ken Herkenhoff: No Targets to Reach, Let's Drive (18 March 2014)
I was traveling again, so was not involved in Sol 574 planning. The Sol 574 tactical planning team considered the option of contact science before driving, but with no interesting targets in the arm workspace, they decided to acquire more ChemCam and Mastcam data instead. Then a drive of about 40 meters is planned toward an interesting outcrop that may be the target of contact science.
Sol 575 Update On Curiosity From USGS Scientist Ken Herkenhoff: Out of Synch (19 March 2014)
MSL and Pasadena times are out of synch, so planning is restricted and Sol 575 is an untargeted science sol while we wait for the data needed to drive again. CheMin, ChemCam and SAM will perform calibration and related activities in preparation for the upcoming analyses at the "Kimberley" waypoint.
Sol 576 Update On Curiosity From USGS Scientist Ken Herkenhoff: "thwack" (20 March 2014)
The Sol 574 post-drive images show nice outcrops in front of the rover, suitable for contact science. This image shows the favored rock face for contact science at upper left. The Sol 576 plan starts with a ChemCam observation of this rock face, plus a Mastcam stereo mosaic of the outcrop. Then the arm will be deployed to "thwack" and vibrate CHIMRA to clean out any remnants of the "John Klein" sample, followed by Mastcam and RMI imaging of the CHIMRA sieve. After stowing the arm, the rover will bump about 2.7 meters toward the outcrop and take the data needed to plan contact science this weekend.
Here's the view they shot after the sol 574 drive, which left Curiosity about 4 meters from the outcrop. If you have 3D glasses you may also enjoy this stereo version. The rock layers here are dipping away from Curiosity, which means the rover sees them almost edge-on, a nice perspective for studying the way in which the layers were laid down.
Here's a view of part of that rock, shot with ChemCam's Remote Micro-Imager, and colorized with Mastcam data. (Here's the Mastcam image that was used to colorize it.) There is a lot going on here.
NASA and JPL issued a news story about Kimberley last week, explaining what it is that the scientists are curious about at this particular stop. All of the rocks appear to be sandstones, and yet they have very different appearances, eroding differently, producing different kinds of landforms. To a geologist, a sandstone is a rock that is composed of sand particles that have been cemented together. As I've explained before, sand means something very specific to a geologist: sand is composed of particles of rock that range from 0.63 to 2 millimeters in diameter. If they're all sandstones, how can they look different? The difference, as they explained in the news story, may have to do with what cements them together. Sand becomes rock when other minerals get deposited between the sand grains, gluing them together. Here's an excerpt:
Material filling the space between grains of sand in sandstone is called cement, whatever its composition. Characteristics of the cement can vary greatly, depending on the environmental history that affected the rock. Sandstones with some clay-mineral cements are quite soft. Tap them with a hammer and they crumble. Sandstones with quartz cement can be very hard. Hit them with a hammer and they ring.
"A major issue for us now is to understand why some rocks resist erosion more than other rocks, epecially when they are so close to each other and are both likely to be sandstones," said Michael Malin of Malin Space Science Systems, San Diego. He is the principal investigator for the Mast Camera and the Mars Descent Camera on Curiosity.
Malin said that variations in cement material of sandstones could provide clues to different types of wet environmental conditions in the area's history.
As in the southwestern United States, understanding why some sandstones are harder than others could help explain the major shapes of the landscape where Curiosity is working inside Gale Crater on Mars. Erosion-resistant sandstone forms a capping layer of mesas and buttes. It could even hold hints about why Gale Crater has a large layered mountain, Mount Sharp, at its center.
So this is the question motivating their investigations at Kimberley. What is holding the rocks together? They will not be able to answer that question with cameras or even with the APXS instrument on the arm. The APXS can tell them what elements are present in the rock, but not the minerals, and it's the mineral information we need in order to answer the cement question. For mineralogy, we need SAM and Chemin, and that means drilling.
Which means it's time to get ready to drill. Preparations for drilling activity began with cleaning and inspection of all of the surfaces of CHIMRA (pronounced "chimera"), the sample-handling mechanism on the end of the arm. Unfortunately, this activity, planned for sol 576, didn't go to completion; look at the images for sol 576 and you'll see several of CHIMRA and then just some Hazcam images. There was a "fault" -- the rover predicted that an activity it was being asked to do with the arm was outside the safety parameters that have been imposed on it.
We're pretty used to arm faults on the Mars Exploration Rovers; they happen from time to time as a part of normal operations. When the rover doesn't think it'll be safe to do an activity, it stops all work and waits for further instruction. This isn't like a safe mode, where something bad actually happened and the rover switches into an emergency mode. Since nothing bad did happen -- the rover only thought that something bad might happen if it continued to follow its instructions -- it stays in its normal operating mode, it just stops executing the sequence that it thinks might cause something bad to happen. Typically, with arm faults, the rover has been instructed to be over-cautious; the rover drivers double-check the commands, adjust some of the parameters that the rover uses to assess its own safety, and re-issue the instructions. The only harm to the mission is lost time. Because the Curiosity mission is currently operating in restricted sols -- where Earth and Mars time has lined up so that the information from Mars arrives too late in an Earth day to use it for planning for the next Mars day -- a fault can mean two mostly-lost sols of work on Mars, though they can sometimes recover some time by doing remote sensing work like shooting photos that doesn't require them to move anything except the mast head.
The fault happened midway through sol 576, but Earth didn't find out about it on the day they were planning 577, they only learned about it in time to plan sol 578, which is when they managed to do most of the stuff that they had planned for sol 576. Partway through sol 578, there was another fault. But they managed to recover more quickly from that one and are now back in business.
So there are lots of photos of CHIMRA spread out over sols 576, 578, and 581, looking at all its surfaces. One rare activity that they performed is something called a "primary thwack," which Ken mentioned was planned for sol 576. A "thwack" is the robot's equivalent of banging your sieve against the countertop to knock out anything that may be stuck in the sieve holes. There's a powerful spring inside CHIMRA that they wind up and then release to give the sieve a bang to knock loose any sediment that may be stuck in the holes. It looks like the thwack was pretty effective, because the sieve looks pretty clean now; but it could have been pretty clean before:
One thing that was mentioned at the briefing is that they are being cautious to avoid a causing a potentially serious problem within CHIMRA, the set of devices on the turret that collects, sieves, and portions rock powder. Dan Limonadi explained at the briefing that three identical units were built; two have been in use on Earth for testing, and one is on Mars. One of the Earth units developed a problem about halfway through its design lifetime involving the 150-micrometer sieve, the one that separates out powder fine enough to be dropped into Chemin. It was first noticed late last year (some time between the DPS and AGU meetings). "Edge welds" that hold the sieve to its chamber are popping apart, which creates a gap that could allow particles larger than 150 micrometers to pass by the sieve. The same problem has not been observed on the other Earth test unit (which is the one that is installed on the Earth testbed copy of the rover), and they are now watching for it but have not seen it on Mars. The unit that had the popping edge welds survived through its complete design lifetime and the was able to perform its function well throughout the test period. After that, it was pulled apart and subjected to intense study. To prevent the problem from occurring on Mars, they are already changing how they use CHIMRA.
Here's a photo of the sieve that was taken on sol 80, after they scooped soil at Rocknest but before they drilled in Yellowknife Bay. I include it here both to show the locations of the edge welds and as a "before" comparison for the sol 578 image. I don't see any changes.
With the arm inspection finally out of the way, they were able to carry on with their work. They began, on sol 580, with a gargantuan Mastcam-100 mosaic of the outcrop, to give context for their arm work. There are still a couple of frames that haven't downloaded yet; this version of the panorama is still missing the lower tier. It's worth visiting the Gigapan version to explore it in all its glory. I've received several questions from readers about this photo, asking me about things they think seem water-carved. I see lots of cascades of dry material, places where windblown dust has recently fallen downslope. It's a process that's similar to the one that makes slope streaks on Mars but smaller in scale, and it's all dry. According to a later update from Ken Herkenhoff (at the bottom of this post), the Curiosity team thinks that some of the little cascades were triggered by the vibration of Curiosity herself, driving up to the outcrop.
After taking that mosaic, they bumped forward a few meters. Here are Ken's summaries:
Sol 581 Update On Curiosity From USGS Scientist Ken Herkenhoff: Fault and New Targets (24 March 2014)
The Sol 578 activities were interrupted by another arm "fault" caused by a command error, but this error is well understood, and the rover is healthy and ready to resume arm activities on Sol 581. First, ChemCam and Mastcam will observe new targets on the outcrop in front of the rover, then the rover will "bump" toward the outcrop and take data to enable contact science planning on Wednesday.
Sol 582 Update On Curiosity From USGS Scientist Ken Herkenhoff: Still Restricted (26 March 2014)
Planning is still restricted, so the Sol 582 plan includes only untargeted observations. The ChemCam calibration images of the sky we planned for Sol 577 were not acquired due to the first arm fault, so we added them to the Sol 582 plan. SAM activities, in preparation for sample analysis at The Kimberley, were also included.
Sol 583 Update On Curiosity From USGS Scientist Ken Herkenhoff: In a Good Position (27 March 2014)
The bump toward the outcrop put us in a good position for contact science, so it was a busy day for me as MAHLI/MARDI uplink lead. We planned an APXS raster (5 positions) on the cleaner vertical face of the outcrop, with MAHLI imaging of each APXS spot. In addition, ChemCam and Mastcam observations of a target dubbed Hooper were planned.
Look at all this juicy rock:
And now they have the arm on it:
The spot where they're sitting now turned out to be a nice one from which to inspect the dune fields that lie a ways away to the south. The embedded version of this panoramic view really doesn't do it justice; you have to zoom in. On the extreme left side, the dunes are a couple of kilometers away, close enough for us to make out the ripples riding up their backs. Toward the right the dunes are farther away, more like 4 kilometers, and those ripples too hard to see.
As I was wrapping up this post, Ken Herkenhoff posted one more update:
Sol 584 Update On Curiosity From USGS Scientist Ken Herkenhoff: Layers and Landslides (28 March 2014)
MSL planning is still restricted, but because the rover has not moved we were able to plan more targeted contact science on Sol 584. After ChemCam and Mastcam observations of a couple nearby rock targets, a big mosaic of the recessive layers in the outcrop in front of us is planned. Then MAHLI will image a couple of small landslides (visible here) that were probably caused by vibration of the surface as the rover drove up to this outcrop. The contact science block will conclude with MAHLI images of Pandanus Yard. But that's not all--after more ChemCam and Mastcam observations late in the afternoon, APXS will integrate and CheMin will perform a calibration analysis overnight. It was a busy planning day!
By the end of the weekend, look for Curiosity to have packed up work at this outcrop, and to have driven back and toward the east edge of Kimberley. It will still probably be at least a month -- through April -- before Curiosity has completed work at Kimberley, assuming no more faults slow us down. It will have taken us about 300 sols, all told, to get to Kimberley, which is about halfway to Murray buttes. I don't believe they'll make much faster time on the second half of the trip, so it's beginning to look like it'll be 2015 before we get to those dune fields and the rocks at the base of Mount Sharp.