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Mission Update by Steve Squyres

(Return to archived mission updates list)

May 2005
May 28, 2005

Nothing really new at Meridiani. We're seeing slow, steady progress, at a remarkably constant rate. For every meter of wheel turns that we command, we get half a centimeter of actual motion. It's been like this since the start of the extraction process. We're typically doing 12 meters of wheel turns a day, and typically seeing about six centimeters of motion. We'll get out of here eventually, but it's a slow, laborious process.

At Gusev, though, the progress has been rather more satisfying. We're starting to understand this place. What we've got is a thick sequence of layered rocks, dipping gently to the northwest. As you go up and down the sequence, there is a remarkable diversity of textures. Some rocks, like Watchtower, which we saw at Larry's Lookout quite awhile ago, are massive. Others, like Keystone at Methuselah, are finely laminated. Still others, like Keel at Jibsheet and like a new one called Ahab that we've just found on the eastern side of Larry's Lookout, have an unusual bulbous or globular texture. So texturally, the rocks in this sequence are all over the map.

Despite the huge diversity in texture, though, all of these rocks have the same chemical composition. Every single rock we've looked at in this region shows a distinctive chemical "fingerprint" of high titanium, high phosphorous, and low chromium. They're all fundamentally made of the same stuff.

But then, despite the constant chemistry, the rocks show an enormous range in how severely they have been altered. Alteration is something we can assess with our Moessbauer spectrometer, and the Moessbauer spectra of these rocks are incredibly diverse. Keystone, for example, is only lightly altered, with plenty of the mineral pyroxene in it. Paros, on the other hand (which, like Ahab, is on the eastern side of Larry's Lookout) is one of the most heavily altered rocks we've ever seen at Gusev. And some of the most-altered rocks contain the mineral goethite, which is a clear sign that their alteration involved water.

So what are we dealing with here? Our best bet is that this is a stack of "volcaniclastic" rocks... granular rocks of volcanic origin. Some of the rocks may have formed by violent eruptions, followed by ashfall from the sky or hot, ground-hugging flows. Others may have formed when volcanic deposits were "reworked" by other processes, stirred up and redeposited. The very constant chemistry suggests that all the layers in the stack came from a common volcanic source.

We're still working out some of the implications of the alteration. Is the alteration greatest at the bottom of the stack and least at the top, indicating a decrease in alteration processes with time? Or does the alteration also vary laterally, with rocks of the same age that are only tens of meters apart showing very different amounts of alteration? This is the piece of the puzzle that we're still struggling with, taking lots of Moessbauer measurements and trying to work out stratigraphic relationships between rocks in different outcrops. It's an important question, because it's related to what the water was doing.

And I wouldn't say that we're 100% convinced yet that these are volcaniclastic rocks. While it seems like the best explanation, we haven't ruled out the possibility that they could have been formed by impacts. Impacts are violent explosions too, and impacts certainly were happening on Mars billions of years ago when these rocks formed. These don't look anything like impact deposits on the Moon, but Mars has an atmosphere, and back when these rocks formed it may have had a more substantial one. So it's possible that martian impact deposits could look like this too. We're keeping our minds open to the possibility, and looking for clues that might settle it definitively.

Finally, an interesting side note. If some of the rocks are highly altered and some lightly altered, but they all have the same amount of phosporous in them, that suggests that the phosphorous was primary. In other words, the phosphorous was in the rock before any alteration took place, not put there by the alteration. When we first saw this high phosphorous signature, all the way back at Wishstone five or six months ago, our initial suspicion was that it was in phosphate salts that had been deposited by water. But it's looking now like this stuff was phosphorous-rich from the git-go.

May 18, 2005

Gradual progress. To extract Opportunity from her little predicament, we've commanded a total of 12 meters of wheel turns so far... 2 meters, then 2 meters, then 4 meters, then 4 meters. We've seen slow, steady progress each time. We're going to kick her into a slightly higher gear today, commanding 8 meters of wheel turns, and we'll see what we see. Optimism continues to run high.

At Gusev, Spirit has arrived at a safe standoff position for observing the eastern side of Larry's Lookout. We're going to sit here and do some serious Pancamming for a sol or two, and then we're going to have to decide what comes next. There are a bunch of possibilities, and we're going to have a very interesting time choosing among them.

May 16, 2005

Sorry I haven't done an update in awhile! I was on the West Coast most of last week and my laptop died while I was out there, cutting me off from the world for a little bit.

We have begun the extraction process at Meridiani. So far we've executed three sols worth of activity. On the first one we simply straightened the wheels, which worked fine. The next two sols were executed over the weekend, and each commanded two meters worth of wheel turns. We were pleased with the outcome of those, too. The rover moved more than a centimeter in the expected direction during each maneuver, which was just the kind of behavior we were hoping for. (In fact, the motion was actually more than I was personally expecting to see this early in the game.) We clearly moved some soil in the process, and there was an encouraging amount of clearing of caked-up debris from between cleats on some of the wheels.

We'll be continuing to work at this over the coming week. Each day, for the next few days at least, we'll command some number of meters worth of wheel turns, based on the results we got from the prior sol. Today we chose 4 meters, based on the good progress that each of the 2-meter sols gave us over the weekend. After that we may keep it at 4 meters for awhile, drop it back to 2, or bump it up to something even higher, depending on what we see.

Anyway, we're real pleased with the results so far, and we'll keep chugging away, bit by bit, until we're out.

Over at Gusev, life is good. We've finished our work on Jibsheet, the composition and texture of which both fit nicely into an evolving story that we have on all the rocks here on Cumberland Ridge. With Jibsheet done, we're now planning a drive back toward Larry's Lookout. This will be a long one, at least by Columbia Hills standards, but since it's mostly downhill we expect it to go pretty quickly. The plan is to drive to a point that's on safe ground a few meters shy of the east side of the Lookout. There are some rocks there that lie stratigraphically older than anything we have seen yet... in fact, they may be the oldest rocks that we have yet seen at Gusev. We'll look at them from a safe distance first, and see what we see. After that, we've got some decisions to make. Back when we had lots of dust on the solar arrays, we had to get around to the south side of Husband Hill quickly or the rover would die. With clean arrays now, though, it's a different world, and we've got a lot of options. We're going to be making some very interesting strategic decisions with Spirit over the next couple of weeks.

May 7, 2005

Okay, we're going to be ready soon to start making our move at Meridiani.

This has been a long, hard week of testing. We tested with one mix of materials, decided it wasn't quite nasty enough, and then made the mix nastier and tested again. We tested getting the rover stuck and then unstuck in a bunch of different configurations, some of which we think were worse than the one we've gotten ourselves into on Mars. The goal of this kind of testing is to be "conservative"... to test under conditions that are at least as bad as -- and preferably worse than -- what you're dealing with in reality. You can see pictures of one of the test setups on the JPL MER web site, though the pictures don't really do justice to all the work that was done, or to all the different kinds of tests that were run.

Then, once we'd done the testing, we brought in a panel of experts from outside the project to give us an independent review of whether we'd done things right or not. Like conservative testing, outside reviews are standard operating procedure in the space biz.

So soon it'll be time to put what we've learned into action on Mars. We've learned quite a bit, and one of the things that we've learned is that it can take a lot of wheel turns to move the rover from a configuration like the one we're in. And while it's tempting to go for it all in one shot, the smart approach is to be cautious about it and do the job in small steps. So that's what we're going to do.

And here's something to keep in mind: The early steps in the extraction process don't look like much. The wheels turn and turn, and even though you're making crucial progress, moving soil bit by bit beneath the wheels, the rover itself hardly moves... sometimes for quite awhile. So when we do begin the extraction process and you see lots of evidence for wheels turning on Mars but not much movement by Opportunity, don't worry... that's exactly what we're expecting. Like the testing, this is going to take awhile.

Over at Gusev, we've finished up our work on Methuselah and done a nifty, complicated little one-sol drive over to a close standoff distance from Jibsheet. The purpose of the standoff is to let us take some good Pancam images over the weekend to plan our attack, just like we did a couple of weeks ago with Methuselah. (And, in the meantime, it also lets us do some IDD work on soil, which we haven't done in quite awhile.) After that, we'll see what we see. Jibsheet is a much tougher target than Methuselah was... tall, rugged, and with a steep and slippery-looking sand slope below it. The Monday morning Spirit SOWG meeting will be an interesting one.

May 4, 2005

We've made some substantial progress over the past week in getting ready to get Opportunity out of the drift that she's driven into. All the action so far has been on Earth, doing testing with the two rovers we have on this planet. It's been nasty work... shovel-and-wheelbarrow stuff, moving around literally tons of fine-grained soil. Rob Sullivan from the science team came up with a "recipe" for a soil mix that rather nicely matches the properties of what we've gotten ourselves into on Mars. Jeff Biesadecki has led the charge from the engineering side, pulling some very long hours in the testbed driving the rovers into and out of the dirt, working out the best way to do it on Mars. We're still testing, and it's going to be a few more days, at least, before we're ready to try anything on Mars. So patience is still necessary. But there are some very good people out at JPL working very hard on this problem, and I remain optimistic that we're going to be out of this stuff and on our way again before too long.

Over at Gusev crater, wonderful things have been happening. We took an enormous Microscopic Imager mosaic on Keystone recently: 4000 by 6000 pixels, the most MI frames we've ever taken on a single rock. The resulting mosaic is stunning, and it reveals Keystone to be finely layered and with a strange porous texture.

The big surprise, for me at least, was the composition. I was expecting Keystone (and by inference all of Methuselah) to be rich in sulfates, like the rocks called Peace and Alligator that we found some time ago. I based this expectation on the fact that Keystone looked a bit like Peace and Alligator in the MI images. Instead, Keystone turns out to have a composition much like Wishstone, a massive-looking piece of loose rock that we encountered during our climb to Larry's Lookout. Like Wishstone (and like Larry's Lookout) Keystone has lots of titanium and lots of phosphorous in it... a distinctive chemical "fingerprint" that many of the rocks on this side of Husband Hill seem to share.

The really good news is that we now have emerging the first true stratigraphy that we've seen in the Columbia Hills... a suite of stratified rocks that we can put together into a time-ordered sequence and work out a history of geologic events. We don't have the whole story yet, but it's really coming together now. I'm hoping to be able to report on it at the American Geophysical Union meeting that's coming up in New Orleans in a few weeks.

In order to add to our emerging understanding of this stratigraphy, we've planned out our moves with Spirit for what'll probably be the next couple of weeks. We're just now finishing up some arm work on "Pittsburgh", another target on Methuselah. After that, we're going to leave Methuselah and head back to an outcrop named Jibsheet that we passed by on our way up the hill. And after we've learned what we can there, the plan is to head back toward Larry's Lookout once more, this time circling around toward the eastern side of the Lookout. There are some rocks there, down low on the outcrop, that we have become very interested in...