MER press briefing, February 9, 2004
February 9, 2004Edit
Natalie Godwin: Both rovers are on the move on Mars. 3:30am at Gusev, 12 hours later on the other side of Mars.
Tim McElrath: As you saw with Spirit, a variety of ways to perform localization on the surface. I'm going to talk about radio data. We'll also hear about descent images and IMU propagation, then post landing MOC images. First graphic shows THEMIS imagery. Blue ellipse is based on tracking during approach. 44 miles long, 5 miles across. When we got to Mars we were fortunate and had two DSN complexes in view. So we had tracking data from Canberra and Goldstone so that gave us differenced one-way doppler data. 5 minutes after EDL we got the tracking data all the way down to parachute deploy. That's the black ellipse which we were able to come out with about 35 minutes after landing. That's about 5.3 miles by 1.4 miles. That confirmed several things we'd seen with relatively late parachute deploy and narrow descend. Needed to wait 'till we were on the surface to get a much closer tie on where we were. On the surface we have 2-way doppler tracking DTE and we also have UHF 2-way doppler tracking to Odyssey which comes over twice a day. That little white ellipse is 145 ft. by 3 ft. from two Odyssey passes and 6 DTE communications spread over 3 sols and that pins us down quite well in an inertial frame but problem is that the map is not tied in well with the inertial frame, could be off as much as a quarter mile but turns out much better at only about 500 feet. Since we've got the map tie solved for this location, we can get the same type of location resolution if we need it.
Andrew Johnson: I'm gonna talk about the second way we determine position. This is using EDL telemetry. This is a mosaic of the three DIMES descent images and a line showing the path that Opportunity took. Over to the left is the direction we're coming in from, going basically East but near the end start moving to North and when we cut bridle we are actually moving North. Another view of the same scene what it shows is the descent trajectory coming down and bouncing along the surface. Final graphic is another blowup of the bouncing across the surface. 26 bounces official number of bounces. We bounced along and some how ended up in this crater :D We rolled 200 meters, about 1/8th of a mile for more than 1 minute. Velocity when we cut loose of the bridle was 9m/s N 2m/s W which is 20mph N 4.5mph W.
Tim Parker: How many golfers out there ;-) First graphic is to look at the horizon views from lander and compare to features seen from orbit. Mosaic of 3 images, far right is 18-20 m/px THEMIS vis image. The next image covers most is a MOC image and the final image canted at an angle there is one of the DIMES images. Here is the reconstruction based on triangulation to three craters visible on the horizon. One was visible pre-standup mission success pano. The other two were seen in post-standup pan. The large crater to the east was obstructed by the rim of the crater we're in. This was difficult because the crater we're at was so small that we can't identify features in it's rim to compare to orbiter views. We've zoomed in here on the last prediction from DIMES team on where the first bounce would have occurred in green and the blue diamond is the last nav solution for where we wound up. That is a remarkably close match to where we actually are with respect to the surface. It's only 120-130 m from the center of the crater. That's far down in the noise with respect to our precision of tying the Mars surface to the geodetic grid.
Mike Malin: As you know, I have a camera in orbit of Mars and it flies over the landing site twice a day, once in the morning and once in the afternoon and we've attempted to take pictures of the landers from this camera which has a nominal 1.5m/px resolution but we can use the spacecraft to assist us in getting "super-resolution" of about 0.5m/px and I'm going to show a combination of both resolutions. This is a picture that shows the overall area, the large crater to the right was in the right side of Tim's picture. If your eyes are really good then you can see that crater that had the lines coming from it in Tim's picture has a little dot in it. That dot is the lander. There are other things on the picture as there were with Spirit. We see going from right to left where the heat shield hit. We see a plume pattern where the retro-rockets fired and where the first bounces occurred. We also have a track of all the bounces. At the far left is where the back shell and parachute hit. This is a picture of the vehicle. One of the things to note is how bit it is relative to the crater. The lander fills a fairly sizable portion of the crater. If you'll go to the next picture, I _believe_ :D that we are actually seeing the rover. The rover will not be right because it has dark solar panels. Not at the right angle to see them glint. Won't know for sure until I take another picture after the rover has moved. One of the fun things is that I knew where everything was and about the same hour, a picture we had taken with the Navcam a couple of days earlier had finally came in and it included in the upper corner a view of the back shell and the parachute from the lander, in the direction you'd expect and the right distance. Justin Mackey first saw it. Pancam team took a special picture of it. Really evocative. At the very bottom just off the edge is the crater rim. Outside the crater showing you the parachute and the back shell. That's a view out over the rim of the crater looking out across this vast flat surface and there is the hardware that we've littered the surface with. A nice view. Steve's gonna tell you about some really neat science.
Steve Squyres: OK. Let's see. Where to begin. We had a big weekend, probably the biggest three days of science since we landed. I've got a lot of stuff to show you. Start at Meridiani where the really crazy stuff is. The deeper we get in, the more it reminds me of a mystery novel. You get clues, kinda one at a time. Some of them mean something, some are probably red herrings, you don't know which is which. We're working our way through the clues here. So what I've got is a few more, some pretty tantalizing ones of what we're seeing here at Meridiani. Video shows the familiar outcrop that we've named Opportunity Ledge after the spacecraft that found it. At the far right is this rock we originally named Snout, now named Stone Mountain - we tend to pick quick names sort of in the heat of battle and then we come back with something better later. You'll see a Pancam image as we zoom in. This is a color Pancam that shows this outcrop in detail for the first time. This pretty close to true-color. It is buff colored, or tan, finely laminated, thickness of layers a few mm at most. And then, embedded in it, like blueberries in a muffin, are these little spherical grains I'm calling spherules, spherical granules, because we don't know what they are yet, though I'm gonna run through the theories. They are different in color. The spherules are very, very gray - much, much different from the matrix they're embedded in. This next image is false color generated using infrared bands processed to really bring out those bright dots in the outcrop. Those are the spherules and this emphasizes the point that they are different in color and that's a hint that they may be different in composition which could be a very important piece of information. We drove up to this guy and slapped our instruments down on it. I'm going to show you some Microscopic Imager pictures and what you will see is wild looking stuff. You can see the layers, inherently very, very fine-grained sitting there for millions of years being sandblasted. This stuff sits there, the wind blows, these grains are striking and eroding the softer portions developing this intricate texture telling you how well indurated the rock is. Then embedded in the stuff are the little spherules. Those seem to be pretty tough. So what happens is that the rock erodes away as it gets sandblasted and the little blueberries drop out and roll down the slope where we take pictures of them. There's one in the process of being eroded out. Look at this next MI image. Look at this guy. One of the spherules broken in half. it's hanging out there. If you look carefully and follow the crack that runs upward from that running diagonally. Follow that crack and there's another one, and another one, strung like beads along that crack. I think there are 4 of them. This rock is being eroded away and the spherical grains are dropping out. Now, there are some things here that we know and some things that we don't know. I'm going to take you through the hypothesis still standing. There are several still standing. For the matrix, there's really only two ideas still holding up, that it's volcanic ash or wind-blown dust compacted into a sedimentary rock. This is so fine grained. It ain't a sandstone. Either some kind of ash or stuck together indurated dust. As for the spherules, there are three hypothesis still open but one fading fast. The idea that it's lapilli is fading fast. I wouldn't rule it out yet, we go back and forth. Remember, lapilli form when you have suspended ash above a volcano and the ash agglomerates forming spherical balls that fall out of the sky. The thing is that they tend to be made of the same stuff in which they're embedded. Now we don't yet have, say separate Mossbauer on the matrix and the spherules. We're gonna do that and I think that'll really nail it down but the fact that their spectra are so different suggest to me that they're made of different stuff. So that's one hypotheses but running in 3rd place. Other is that it's some kind of spherical grains formed when molten rock is sprayed into the air, freezes in air, and these droplets of rock, made in impacts, a high energy volcano, fall down on the surface. Third possibility is that they're what geologists call concretions. Concretions form when fluids carrying dissolved stuff diffuses through a rock and precipitates around a nucleus and it grows little spherical granules within the rock. We think we should be able to test all of those. What we're planning over the next few sols is a thorough survey of this outcrop, what we're calling a shoot and scoot where we shoot a bunch of pictures, scoot over about 3m and shoot some more, getting Pancam and mini-TES shots and then we'll find a couple of the best places and go hit 'em with everything we've got. What do I mean by best? For example where the matrix is really well exposed and we can go in with the RAT and see what those layers are like. What I'd really like to find is a place with a bunch of these spherules, RAT across those and see what they look like in cross-section then stick the Mossbauer up against them and see what they're made of, see if they're different from the matrix. One other teaser, a clue that just popped up, not gonna quote any numbers yet, but we have now completed an APXS measurement on the outcrop and it has got a lot of sulfur in it, maybe a few times more sulfur than we've seen at any other location on Mars. So that's what's new on Meridiani so let's go on to Gusev. This is the RAT and our old friend Adirondack. Adirondack looking a bit different thanks to Steve Gorvan and honeybee robotics team have had their way with this rock. It has really opened up a window into the interior that we can use to understand it very well. Pancam image where RAT has ground a hole 2-3mm deep. Next image shows before and the next image shows brushed off and next image shows cut away. Beautiful cut, polished rock surface. Looks like a basalt and Mossbauer and APXS confirm that it is indeed a volcanic basaltic rock. We know what it is. Time to move on.
Mark Maimone: We've had a very busy day. Both rovers drove on the surface of Mars. Opportunity in the last few hours drove another 4 meters on the surface. Earlier than that the Spirit drover drove a long drive of about 6.4 meters. We have an image to show you the trail behind the Spirit rover. See the tracks. Lander out of view. See the back face of Adirondack. It may have looked really big but we drove right over it. Another interesting thing is that this was a drive to get to White Boat, a small white rock but also the first test on Mars of the rovers Autonomous Navigation System. That means the rover was in charge of its drive. The people on the ground tell it where we want it to go but it decides how to get there. That opens up new opportunities and distances. We can only plan so far in the images we see. What's gonna happen now is we start to let the rover make its own decisions. It takes a look in front of it, builds a map, avoids the red, goes on green and yellow. This animation shows the process inside the rover's brain as it drives on the surface of Mars. This will continue. What's nice is that until yesterday, the Opportunity rover was leading the game but Spirit tore out ahead with a total distance of about 12.5 meters. Though I just learned that Opportunity moved another 4 meters so it's up to 13 :) Not that anybody's counting. The race is on. Our plans are to explore the crater at Meridiani and at Gusev going for very long drives. Not sure exactly how far they'll be because it's up to the rover to decide how safe. We're going to let it choose its path for some of the way.
Q. Can you elaborate on the concretion model for the spherules and do any of those, how those form, exclude the theories about how the rock layers form?
Steve: I think the idea that they're lapilli would only work with the matrix being volcanic ash. Those two are tied together. With respect to concretions, if you have fluid, water with dissolved stuff in it flowing through a sediment, it can precipitate minerals, stuff that's dissolved in the water, and commonly will nucleate in a spot and this concretion will grow and grow in a spherical fashion. These are found in a variety of settings on the earth. By making observations about how these round things are related to the layers, we can test distinguish between the various hypothesis. For example, if you have a nice layer in the sediment, and then you grow one of these concretions you might see the layering preserved within the concretion. So if we see one of these spherical guys in place with a layer running through it, that would favor the concretion idea. If, on the other hand, you've got layers forming and you've got these things falling in from above, as would be the case for the droplets of glass, it might deform soft layers so by taking many MI images and looking at the relationships I think there's a good chance we'll be able to distinguish on just the shape of this stuff. Then of course the composition will be revealing.
Q. Steve, you mentioned that several hypothesis standing earlier have been ruled out. Can you go through what's been ruled out? Oolites no longer in the running?
Steve: When we first say these layered rocks from a distance there were a bunch of possibilities. Reasonably fine layers could even have been some kind of lava flows. That was ruled out when we saw how thin these layers were. I think that the idea that this was some kind of course-grained sedimentary rock, a sandstone or something like that is ruled out by the high-res MI pictures. These look the way they're weathering like a very fine-grained ash or sediment. Spherical grains. One way to make round things is to tumble them. That's ruled out by the fact that they're round while still embedded in the matrix. Lapilli, I'm still clinging to that one but compositional evidence not in favor. Another thing you might think about are something called ooids, grains that are rounded and created in a wave environment. I didn't list it with the theories because I don't think any of us consider it to be particularly likely.
Tim Parker: I think that if it were oolitic, we'd have layers that were predominantly oolitic.
Steve: Yes. When you see this, they tend to be really clustered together and not just sprinkled a few here and there.
Q. To go back to the hematite, where does it lie and looking outside,
Steve: When we look at the outcrop from a distance with Mini-TES we don't detect hematite. The matrix itself does not appear to be hematite bearing. That does not rule out that the spherules might contain the hematite. Can't tell with mini-TES because the mini-TES spot on the outcrop is maybe 8 inches and so it's seeing maybe 99% rock and 1% spherules. The key to answering that is gonna be to use the Pancam to find a place with a lot of these spherules, RAT it, and look at it with the Mossbauer. There's no question though that the highest concentration of hematite is actually above the outcrop and we don't know what's up there. Everything we're seeing so far is either the outcrop itself and some of the stuff that's fallen down. Some that's fallen has fallen from the outcrop and some maybe from above. We can't tell with the granules in the crater in front of us, their pedigree is unknown. That's the nice thing about the spherules in the outcrop. You know where they come from. The evidence suggests that the highest concentration of hematite comes from up above the outcrop layer that we're not gonna see until we start to climb out of this crater. I would be very interesting to see if there is hematite in the spherules.