I always found the contrast between Soviet and US engineering fascinating. The goals were generally similar, but while the US seemed to aim for elegant, lightweight, optimized designs, Soviet spacecraft always look like they’re bolted together out of cast iron or something. That’s why I love this gallery of photos of the Soviet lunar lander that they developed during the space race. This thing looks like it should be used for deep sea exploration! Between this, and the always-awesome Lunokhod rovers, I’m pretty sure the Russians inadvertently started the steampunk movement.
Categories: Fun Stuff, Humans in Space
Categories: Astrobiology, Clays, Craters, Current Research, MSL, NASA, Water on Mars
We wrapped up the landing site workshop on wednesday afternoon by revisiting each of the four sites and discussing them in turn. Unfortunately, the way that we did this was very disappointing, and made for a frustrating afternoon.
The discussion was centered around a word document that was projected up on the screen in the room. Over lunch, the meeting leaders had conferred and listed what they thought were the key points for each site that everyone agreed with, along with areas of future work. But they should have known that getting a room of 200 scientists to agree with something is nearly impossible, and it didn’t help that their list of points was a mish-mash of actual, irrefutable observations (e.g. “there are strong clay mineral signatures at Mawrth”, or “there is a huge layered mound at Gale”) and complete speculations (e.g. “the delta at Eberswalde preserves organic molecules” or “the layered rocks at Holden are likely lake deposits”) and everything in between.
The result was that we spent most of the afternoon going through this document line by line and debating word choices and phrasing and grammar. It was incredibly frustrating, to the point where I almost had to leave the room. By the end, there were probably only five or so people actively participating, while everyone else in the room silently suffered through watching this document being written by committee.
After the discussion, we did end up with a central hypothesis for each of the sites, along with a list of future work.Gale was the first site we discussed, so a lot of the time was spent figuring out how we were going to do this document editing as a group. I also was on the edge of my seat because my adviser was off the the side telling me that I should chime in. I always get stressed out when I’m expected to comment or ask a question when I don’t really have a comment or question to make. In the end I asked about the wording of one of the bullets that said Gale has a “relative paucity of fluvial channels”. Because it actually has tons of them. But apparently “relative paucity” meant “there is more volume in the mound than could have come from those channels” so the sentence was not edited. Those two things mean different things to me, but I didn’t press the point.
Anyway, all of that meant that I didn’t take careful notes for Gale, but the final hypothesis was something along the lines of “how do the environmental and mineralogical signatures preserved in the layered rocks reflect the aqueous processes in the crater?” Although someone else suggested a more concise and to-the-point version: “Did the big-ass mound form in a lake?” Future work for Gale included getting a better handle on the age of the deposits and identifying specifically where MSL would go to look for organics.
For Mawrth the process was a little smoother, but still painful. I don’t know how professional scientists can have so much trouble stringing together a coherent set of words. in the end, the hypothesis they came up with was: “Mawrth records geologic processes during early martian history when aqueous phyllosilicate-forming processes were pervasive and persistent and provides the opportunity to understand early habitability.”
Future work for Mawrth was to figure out the timing of the formation of the stratigraphy and the mineralogy, and just generally getting a better grasp on the possible depositional settings. There was also the question of what MSL would do on an extended mission, and Jean-Pierre Bibring called for astrobiologists to take a look at the site and try to fill in that part of the story.
By the time we got to Holden, the process for the discussion was in place, and the site advocates had had time to write down a hypothesis. unfortunately, it was wordy and awkward and immediately had to be edited, but in the end it boiled down to: “Holden preserves evidence of a fluvial-lacustrine system that provides the opportunity to apply a systems approach to evaluating a sustained, habitable environment.”
For Holden, the future work was to see if we can learn anything more about the light-toned layered deposits to see if they were formed in a lake. Also, looking at the orientation of the layers in the site was mentioned specifically.
Finally, Eberswalde benefitted from watching all of the other sites go first, and the fact that it has the clearest hypothesis to test of any of the sites. Sanjeev Gupta delivered this hypothesis: “Eberswalde crater’s stratigraphy, geomorphology and mineralogy records the evolution of a crater lake and associated fluvio-deltaic systems and additionally represents a habitable sedimentary environment that is favorable to the preservation of organics.” This one was clear enough and well worded enough that people actually applauded when they realized we wouldn’t have to agonize over the wording.
I don’t have notes for future work for Eberswalde, but I am pretty sure it included looking more carefully at the minerals seen from orbit and identifying specifically where to go to access the “bottomset” beds, which should have the best chance of preserving organics (the Eberswalde presenters repeatedly answered this question – you go the the bottom of any preserved stratigraphy – but people seemed determined not to hear this answer)
There was also a repeated call for all of the sites to identify specific targets for MSL to investigate, which can be fed into the rover drivers’ attempts at estimating how long it will take to get to the primary targets of each site.
So, that wraps up the 4th MSL landing site workshop. We didn’t vote any of the sites “off the island” this time, but I can tell you the impression that I got. I think Eberswalde is the clear leader among the four sites because, if you’re going to look for organics on Mars, it is the only place where we can be confident that there was a low-energy depositional environment that would concentrate and preserve organics. Based on the vibe in the room, I think Mawrth would come in second place if we had voted. Even though we have no idea how the rocks there formed, they have the undeniable advantage that you land on your primary target. Also, their team has always been a very cohesive and outspoken group at these meetings. They can be annoying in their fanaticism over their site, but I think their disciplined messaging may have had some influence.
I think Gale crater would come in just behind Mawrth. It has a lot of great qualities: including clear detections of both phyllosilicates and clays, and a very thick stratigraphic sequence that would tell you about a lot of environments. But Gale is a go-to site, and even though I showed a lot of cool stuff in the ellipse, people are a bit uncomfortable with the go-to sites. Gale particularly worries people because driving up a big mound sounds risky. We saw that based on slopes, there looks to be a clear path up the mound, but i wouldn’t be surprised it the rover drivers end up telling us it’s going to be extremely slow to climb it. The other issue is that we can’t say for sure what the mound is made of. It might have formed in a lake, but then again it might not have. This is true for all the sites except Eberswalde, which is pretty clearly a delta, but it seems to be emphasized most for Gale.
Finally, I think Holden would come in last. The Holden presenters did a great job highlighting all the good science that can be done on the alluvial fans in Holden, and with the go-to targets. But Gale has many similar features, only more-so. At both sites you land on an alluvial fan and then drive to layered rocks. Except the rocks at Holden are 100s of meters thick and the rocks at Gale are 1000s of meters thick. Holden does have nice examples of pre-impact breccia as well as the flood deposits, neither of which you would get to see at Gale, but those targets are toward the end of a long traverse at Holden, and may not tell us much about habitability.
So, that’s how I think the voting would go if we had voted at this meeting. My own ranked order shuffled around throughout the meeting: each site made a very convincing argument, so tended to jump higher on my list until the next site presented its case. Now, with a few days of perspective, I would rank the sites in this order: 1. Eberswalde, 2. Gale, 3. Mawrth, 4. Holden. I personally put Gale ahead of Mawrth because even though we don’t know the depositional setting for either site, at Gale there is enough stratigraphy that you get multiple chances to find a habitable environment.
Of course, there are caveats to this. If Eberswalde really did form from melted runoff caused by the Holden impact, that might knock it down on the list. If we can figure out the depositional environment at Mawrth and it’s not just impact ejecta, that might bump it up in the ranking.
The bottom line coming out of this meeting is that there is still a lot we can learn about all of these sites. Some of it can only be learned by a rover, but some of it just requires a deeper look at the data we already have. MSL is a phenomenally powerful (and phenomenally expensive) machine, and we only get one. I hope this meeting gets people digging deeper to learn about these sites so that we send MSL to the best place possible, whatever that may be.
Categories: Curiosity, Engineering, MSL, NASA
With the details of all four landing sites on the table, we started day 3 of the meeting by hearing from the engineers and several scientists about the properties of the ellipses, the risks for landing and the capabilities of the landing system. First on the schedule was Mike Watkins, who explained why MSL is so unique in terms of assessing the risk for the landing site because the landing safety is essentially the same for the sites, so the tradeoff becomes more science-oriented and requires a lot more knowledge of the possible targets and traverse distances.
After Watkins, Ashwin Vasavada – the deputy project scientist – told us about the atmospheric simulations that his team has been doing to make sure the weather at the sites won’t mess up the landing system. He pointed out that we are one mars-year away from landing: “The next time Mars goes around the sun, we’ll be there to meet it.” That means that measurements being made right now will be really important in predicting the conditions when MSL arrives. It turns out that unlike previous missions, MSL will actually fly for about 100 km at a pretty constant altitude. This guided flight is what shrinks the ellipses down to nearly circular, but it means that we need to understand the weather for that whole distance. It sounds like the weather at the sites shouldn’t be a problem: Vasavada said that MSL should be able to land even if there is a dust storm occurring at the landing site.
Next up, Ken Herkenhoff gave a summary of all the processing that goes into making the high-resolution elevation maps based on HiRISE stereo images. It is incredibly complicated to make these things, but they’re extremely important for planning the landing and traverses. Luckily, the folks at USGS have a lot of really clever techniques to make the products possible. The DTMs are available at the HiRISE website.
Matt Golombeck then gave his first of two presentations. This one was about counting rocks in the landing ellipses to make sure they’re safe. For the purposes of his talk, he defined a “rock” as anything that we don’t want to land on or get in the way. Rock counting has been done for all the previous landing sites on Mars, so we have some good “ground truth” to compare with the rock counts from orbit with HiRISE. They use an automated algorithm to count the rocks and then fit the size distribution to a model based on previous sites to predict the number of dangerous rocks that are too small to count. In the past it has been very successful, and they’re confident that all the MSL sites are safe enough. Golombeck said that Holden is especially safe in terms of rocks: “I think there’s maybe one rock in Holden.” There were a couple of very good questions after this talk. Rob Sullivan asked whether a small softball-sized rock would be a danger if we landed right on it with a wheel, and the answer was basically no. The engineers said that the biggest risk was getting a rock in the belly that would damage the rover and/or prevent it from moving. A second question from Steve Ruff was more generally, “how concerned should we be about landing with a hobbled rover?” The engineers said, again, don’t worry about it. They’ve been investigating some scenarios where the landing system might get stressed beyond the point where the materials have a linear behavior, but they aren’t worried about breaking the rover.
Next up, Robin Fergason presented about the thermal inertia of the sites. Thermal inertia is a measurement of how resistant a surface is to heating. Bedrock takes a long time to heat up and cool down so it has a high thermal inertia. Dust has a low thermal inertia. Fergason said that all the sites look safe in terms of thermal inertia and then discussed some of the details of each site. One thing that sort of bothered me was that she kept saying that lower thermal inertia might suggest alteration. It’s true, it might, but I would never bet a $2.3 billion rover on the fact that altered rocks have slightly lower thermal inertia. The values seen could just as well be
unaltered bedrock with a dusting of sand or dust on top. Of course, we see other evidence that the rocks at the landing sites are altered, but for the rocks with no clear spectral signatures, I don’t think it’s safe to assume they’re altered based on thermal inertia.
After the thermal inertia discussion, Golombeck got up and gave a presentation with 83 slide in 30 minutes, flashing rapid-fire views of lots of different data-sets used to characterize the ellipses. He also told us that the orientation of the ellipses has changed a little bit so that now their long axis is due east-west. Taking a look at the 5 meter slopes he said that Mawrth and Eberswalde were significantly rougher than Gale and Holden (which makes sense, since Gale and Holden both land on top of nice flat alluvial fans). The topography at Mawrth and Eberswalde would be comparable to that seen in the Columbia hills, where Spirit has been exploring. Golombeck also showed that there are very few “inescapable hazards” such as craters in which you could land but then couldn’t escape. At this point he jokingly made fun of engineer Gentry Lee who had been worried about a big crater in the Mawrth ellipse, saying that the crater was not a target rather than an obstacle! There was also the amusing mention of a small mesa in Eberswalde where MSL would land but would have to go down some pretty steep slopes to escape. This possibility was later refferred to as the “Lion King” scenario by Rob Sullivan. It’s incredibly unlikely, but still hilarious to picture the rover greeting the sunrise from atop this viewpoint, which would, of course, be called Pride Rock.
At the end of this talk, Sullivan asked whether there is any concern that dust kicked up by the rockets could confuse the landing radar. The engineeres said that yes, there is some concern, but they are doing tests with the radar on helicopters to learn more. Basically, the engineer responding said “We could probably fly through the blowing stuff. We might not like it, but we could do it.”
Next, Devin Kipp, one of the engineers on the entry, descent and landing teams gave a presentation that took a look at all the things that could go wrong and basically said “we don’t think these things are going to happen”. He said that the chances of landing success in all of the sites are about 98-99%. Kipp also made the biggest understatement and the best example of NASA engineering-speak all day. When discussing the transition from wheel touchdown to actual roving he said: “hopefully the rover-surface interaction perpetuates for the rest of the mission.” I certainly agree with that!
Finally, Paolo Belutta, a rover driver, gave a presentation detailing how the traverse times for each site are going to be predicted. I suspect that these traverse times are going to be the deciding factor for which site is selected. Since landing on the sites is equally safe, the risk gets pushed into the traverse portion of the mission. Belutta is making detailed maps of the sites using HiRISE images and terrain models to estimate how long it will take to drive in any given location. Then, with input from the scientists, he will compute the traverse durations for several options in each of the landing sites. At that point we’ll come to the tough part where we decide whether the cost of a long traverse is worth the possible payoff.
Overall, it was an extremely positive morning and I think it laid to rest a lot of concerns that the science community had, based on rumors and partial information that had spread around the science teams. That said, I think it was also presented with full knowledge that this was a public meeting, and that word might get out if they admitted to any major problems. NASA has this mentality where it is afraid to acknowledge the difficulty of what it does until it has done it successfully. Personally, I think NASA should play up the risks and the difficulties ahead of time: they’re really interesting, and they make the final successes that much more exciting, and prepare people for the worst if it happens.
In any case, it was a fascinating morning. I’ll post about the big afternoon discussion of all the sites tomorrow. Stay tuned!
Categories: Astrobiology, Clays, MSL, NASA, Water on Mars
The final site of the four that we discussed yesterday was Eberswalde, which of course is interesting because of the big delta that is preserved in the western part of the crater.The first presentation on Eberswalde was an impassioned and really interesting talk by terrestrial geomorphologist Bill Dietrich. Bill talked about how Eberswalde is an excellent site for going beyond just making qualitative statements about water on Mars and actually learning quantitative information about the fluvial system. By making surface measurements, Dietrich showed that you can learn things like how much water was actually flowing and what the individual flow events were like. He also talked about the meandering channels in the delta and those seen on the floor of Eberswalde and Gale. Dietrich showed evidence from earth that to form meandering channels you need to have something that strengthens the banks of the river. Typically it is vegetation on earth, but ice, clay-sized particles or chemical cements can also do the job, and MSL would be able to tell which of these it was.
After Dietrich’s talk, my officemate Melissa Rice gave a presentation highlighting the types of things in the landing ellipse. Her talk pointed out that there’s more to do in Eberswalde than just land and drive due west to the delta: there is a consistent stratigraphy in lots of the outcrops in the ellipse, along with chunks of ejecta from Holden, inverted channels, cemented fractures, and other smaller fans. I think her talk eased a lot of people’s minds who wanted to like Eberswalde but were afraid of a long go-to portion with not a lot to do until you get to the delta.
Next up, another terrestrial expert, Sanjeev Gupta gave a talk about the value of a source-to-sink relationship. He started his talk with an aerial photo of a desert landscape on Earth with really complicated geology and had this hilarious quote from when he was a postdoc: “I was ‘skycraned’ into this area, given a three month ‘battery life’ and told to worry about my career.” He went on to drive home how awesome Eberswalde is because you can see exactly where the sediment came from and where it ended up. “Field geologists on Earth would kill to have what we see at Eberswalde.” Gupta also emphasized that at Eberswalde we have a clear testable hypothesis: that the feature observed is a delta that formed in a lake. he also said something that I didn’t know: the slope of a delta is determined by grain size, so the fact that Eberswalde has a very shallow slope suggests very small grain size, which is good for preserving organic molecules.
Kevin Lewis gave a sort of summary presentation that also highlighted a couple of important points. The first is that many of the channels that cut the wall at Eberswalde end at the same elevation, and that elevation matches pretty well with a saddle point where water from the western crater would spill over into the eastern crater. This spillway might have acted like a dam to maintain the water level in Eberswalde at a specific elevation. Lewis also reminded everyone that the presence of a delta gives MSL a “built-in roadmap”: if you want to reach the fine-grained sediment that is most likely to preserve organics, you want to go to the lowest beds in the delta.
Finally, Nicolas Mangold gave a very interesting and controversial talk suggesting that all of the flowing water in Eberswalde may be due to the hot ejecta from Holden crater melting ice. This would mean that Eberswalde could have formed on a Mars that was otherwise not particularly friendly to life and that the lake could have been very transient.
That launched a really vigorous discussion about the site. Ross Irwin claimed that the amount of water required to carve the channels in Holden and Eberswalde was way too high to have all come from ejecta-induced melting. And John Grant pointed to other nearby craters of a similar age that have alluvial fans but would not have been triggered by the Holden impact. There were cries that we need to look for evidence of a shoreline, followed by others responding that it’s unlikely you would see a shoreline.
There were also a number of questions that appeared to me to be deliberate and rather transparent attempts to make this site look worse than Mawrth. Coincidentally, these questions all came from Mawrth advocates! First, someone asked whether all we would really be learning about at Eberswalde is “what sorts of processes form deltas on Mars”. Kelin Whipple responded, saying that if you don’t care about that specific question that’s fine, but by being able to take the study of the hydrologic system to a detailed quatitative level, it teaches you a lot about the climate of early Mars. Sanjeev Gupta also echoed that, saying that the delta gives you information that lets you test the big questions about martian climate.
Another question that I found really pretty absurd, was “how would MSL’s measurements supplement our understanding of Mars beyond “wow! There’s a delta!” I don’t know where this person was when Bill Dietrich and Sanjeev Gupta were giving their presentations. Dietrich very politely recapped his points, that we would go from a qualitative to a quantitative understanding of the system with lots more information about the environment. He countered this question by saying that you could just as well simplify Mawrth down to “Wow there are clays on mars!”
A third example of these rather leading questions was along the lines of: “We’ve been focusing on the structure of this delta, but what do we use all the compositional instruments on MSL for?” The room responded to this one with shocked disbelief before Scott McLennan, a geochemist, pointed out that understanding the context is just as important for geochemistry as it is for fluvial geomorphology.
There was a lot more discussion, but those were some of the more “interesting” questions. I found it rather annoying that the Mawrth advocates asked leading questions that they (I hope!) already knew the answer to in an attempt to make Eberswalde look bad. Still, at the end of the day, I think Eberswalde is the clear favorite landing site. The only troubling thing is the possibility that it could have formed rapidly due to melt from the Holden ejecta, and that is the number one thing to look into before we decide to send MSL there.
To me, Eberswalde is an incredibly strong site because it fits the MSL objectives almost perfectly. It is the only place on Mars where there is a clear place to look where the processes would concentrate and preserve any organic material that was present. It is the best evidence for lakes on Mars, and toward the end of the discussion of the site, Jim Bell had a good comment. He pointed out that there’s this apocryphal story that MER landed in Gusev and everyone was totally shocked that there was lava there instead of a lake bed. He said that actually there was a lot of debate beforehand. For Eberswalde, the community is much more in agreement that there was a lake. It would obviously be a big deal to visit a lake on Mars, but it would also be a huge result if we went to Eberswalde and it turned out not to be a lake!
If you want to read the rest of the discussion of Eberswalde, check my notes. It had, by far, the longest and most interesting discussion session. You can also read ahead to see what we heard about this morning in terms of the safety of the sites, and some sketchy notes of the afternoon discussion. And if you really want the nitty gritty details, the presentations from the landing site meeting are now available online.
Categories: Astrobiology, Clays, Craters, Current Research, MSL, NASA, Water on Mars
The second site that we discussed yesterday was Holden Crater. Ross Irwin gave the first, overview presentation. Holden is a 155 kilometer crater that formed right in the middle of a huge drainage system that spans from the Argyre basin to the northern plains, and at Holden you would land on a bunch of coalescing alluvial fans on the western crater floor and then drive southeast to access some nice phyllosilicate-bearing light-toned layers. Irwin emphasized that even though the light-toned layers are a key target, Holden is all about visiting a bunch of diverse water-related settings. He also made the interesting argument that MSL is likely our only chance, at least within the next decade or two, of sending a plutonium-powered rover to Mars that is capable of landing at a site as far south as Holden and Eberswalde, whereas Gale or Mawrth could be accessed by a later, solar-powered rover. Irwin also gave extremely detailed lists of what science MSL could do at each stop along the traverse. These sorts of lists are exactly what we need to make for all the sites because they really get us thinking in detail about MSL’s capabilities and what we would learn.
Next up was Kelin Whipple, who is an expert on alluvial fans here on Earth. Kelin described in more detail what fans can tell you about the climate when they were deposited (a lot!) and showed that the fans at Holden could be made by mud flows or water flows and that either way they would be really interesting.
After that, James Wray, a fellow Cornell grad student and Goddard ’06 NASA Academy alum, gave a presentation about the mineralogy at Holden. He particularly looked at some of the rocks in the walls of the crater, which would be present in the materials of the fans in the landing site. James found a pretty diverse set of minerals, including two types of olivine, two types of pyroxene, some phyllosilicates and some possible salts or high-silica minerals. James also pointed out that there are some mounds of material in the eastern ellipse which may be outcrops of pre-impact material.
Following James’ presentation, Debra Buczkowski discussed the results of work with Kim Seelos studying what looks like a really extensive layer of phyllosilicate-bearing rock just below the surface in the region to the northwest of Holden and Eberswalde. They found that the clays in Holden that appeared to be in-place were different from those in this extensive layer, but that some of the Holden clays that looked like they had been transported might be the same stuff.
Finally Peter Buhler gave a presentation of his work on a small trough to the southeast of Holden which may also have been a system of lakes, and emphasized that Holden and Eberswalde could give us a “contextualized” hydrology of the broader region.
The discussion started off with a question from Dawn Sumner about whether the alluvial fans on the wall are interbedded with the light-toned layers, or whether the fans are just on top of the light toned stuff. This is a tough question to answer because as alluvial fans form, they advance outward into the basin, hiding everything underneath. Next my adviser, Jim Bell, asked whether all the great science described for the Holden fans could also be done on the fan at Gale Crater, to which Kelin Whipple said “Yes!” although he pointed out that it’s hard to tie the fans to the stratigraphy of the mound at Gale. Another question about Holden was what the compositional variation of the fan material would be: in other words, how far would we have to drive to get samples of different stuff? The short answer was: we don’t know until we get there. But James showed that there was a variety of rock types up in the crater wall. Whipple explained that if the fan was made by mud flows, which tend to come from a very localized source, they each layer in the fan would be different, whereas if it was formed by a more watery runoff flow then it would have a more blended composition.
After hearing the presentations for Holden I felt a lot better about it as a site than I had before, but I still have the nagging thought that it’s very similar to Gale: you land on alluvial fans, then traverse to visit nice layered stratigraphy, except at Gale the stratigraphy is much more diverse and much thicker than at Holden. If I had to guess, based on the vibe in the room, I would guess that Holden and Gale are the bottom two sites in the ranking. Part of that may have been the timing of the presentations for Holden (after lunch lull) so I’ll see how it looks after the more detailed discussion today. As for my own personal ranking of the sites, it has been jumping all over the place as I hear the presentations from each group. I’m very interested to hear what the engineers tell us today, and to see how the giant discussion this afternoon plays out.
Categories: Astrobiology, Clays, CRISM, Curiosity, Current Research, MSL, NASA, Ryan's Research, Water on Mars
Holy cow. Today was jam-packed with interesting stuff about Mawrth Vallis, Holden Crater and Eberswalde Crater! I took tons of notes, and I will try to use those to assemble a coherent picture of what was presented and discussed today. But if you’re too impatient to wait for me to work through those and post the more coherent summary, here are the notes in their raw and unedited form. Read them at your own risk, they’re full of jargon and typos and abbreviations! I’ll update that file tomorrow with tomorrow’s notes too.
In the meantime, I’ll start to translate those notes, starting with the first site on the table this morning: Mawrth Vallis. Joe Michalski started off the day with an overview of Mawrth emphasizing some of the key points about the landing site. Of course the obvious draw for Mawrth is that it is the best exposure of clay minerals on Mars. Clays form in wet environments and are good at trapping organics, so they are very desirable for MSL. Joe (and subsequent speakers) also emphasized that Mawrth also has morphologic diversity and that it is an extremely old portion of the martian crust. Joe also pointed out that the fact that we see lots of clay minerals at Mawrth is not because Mawrth is unusual for early Mars. It’s much more likely that much of the early crust has similar minerals, but Mawrth is the best exposure.
The next talk was by Janice Bishop who summarized the mineral diversity in the site. She showed a bewildering number of spectra from Mawrth, and drove home the fact that the mineralogy observed occurs in the same stratigraphic order all over mawrth and all over much of the Arabia Terra region on Mars, supporting the idea that understanding Mawrth would teach us about a huge section of the planet. One of the interesting things that Janice and others showed is that these compositional layers are observed in some layered rock in the floor of Oyama crater, the huge crater to the west of the ellipse. This is interesting because it is thought that the rocks in the ellipse are older than Oyama, and obviously the rocks filling Oyama are younger. The fact that they show the same mineral stratigraphy suggests that the related alteration came after the physical deposition of the rocks.
After Janice’s talk, Eldar Noe Dobrea gave an overview of the morphology of the site. He showed a lot of nice HiRISE images of the site, and also gave examples of possible models for how the rocks at Mawrth were deposited, including impact ejecta, airfall, lakes and rivers, or an ocean. Eldar also showed a map of the ellipse that was completely peppered with markers indicating that he had observed layers. This was a contentious issue later in the day because Dawn Sumner, a sedimentary geologist who mostly studies the earth, gave a presentation saying that she didn’t see any convincing layering in the ellipse. Eldar also did something that John Grotzinger specifically said was very useful: he listed some of the thinks we don’t know about the site. In particular, we don’t know the origin of the clay-bearing rocks or the clays themselves. We also don’t know the amount of water that eroded the landscape or its pH, and we don’t know much about the dark unit that caps the stratigraphic sequence at Mawrth.
Next up Damien Loizeau gave a nice talk about what we would do on the first day, month and year at Mawrth, and then Jean-Pierre Bibring gave a concluding presentation. Bibring emphasized the great age of the Mawrth Vallis rocks, pointing out that on earth rocks as old as Mawrth do not exist intact. All we have to work with are mineral grains preserved in younger rocks. So by going to mawrth we might actually learn a lot about Mars as well as about the conditions on very early earth.
Finally, as I mentioned above, Dawn Sumner gave a presentation based on her studies of the physical stratigraphy at Mawrth. She suggested that most of the features at Mawrth are due to cratering and that many of the “layers” are either fractures in the rock from impacts, or are not traceable for more than a few hundred meters at most. (Dawn also showed some very cool movies illustrating some of her points, using a new 3d visualization program that some of the other folks at UC Davis have developed called Crusta.)
After Dawn’s presentation there was a discussion period for Mawrth Vallis. One of the points that came up a few times is that the physical stratigraphy that Dawn was looking at is different from the mineral stratigraphy that seems to show more Al-rich clays above more Fe and Mg-bearing clays. There were also comments suggesting that it may actually be desirable to go to a complex ancient cratered surface precisely because it is confusing and there is no good terrestrial analog for us to study here on Earth. Finally, there was a question about the abundance of clay minerals. In mixing models, Francois Poulet claims to see up to 60% clay minerals at Mawrth, based on OMEGA visible and near-IR data. But in thermal IR observations don’t see nearly that abundance. Steve Ruff, an expert in the thermal IR, said that TES does see some evidence of alteration but not at that sort of abundance. One expanation that he suggested is that the phyllosilicates might be poorly crystalline, so that VNIR observations see something but thermal IR doesn’t.
At the end of the discussion of Mawrth, I felt a lot better about the site than I did before going in. There is clearly a lot of good stuff to do there, and it has a couple of undeniable advantages: it is clearly the oldest site, and you get to land on your primary target. But I’m also concerned by what I hear from terrestrial geologists who are very concerned about how much Mawrth would actually tell us about the habitability of Mars. Yes, it has spectacular phyllosilicates, but it’s not clear that they would trap any organics since we don’t know what the depositional setting was. I think despite this uncertainty, if you polled the community, Mawrth would be one of the top two sites.
Categories: Astrobiology, Clays, CRISM, Curiosity, Current Research, MSL, NASA, Ryan's Research, Sulfates, Water on Mars
It has begun! Today was the first of a three day workshop in which the Mars science community (not just those directly involved in the MSL mission) gathers together and hashes out what we know and what we don’t know about the four finalist MSL landing sites.
For me the week actually started yesterday at the MSL team meeting, where we got lots of updates on the various aspects of the mission. Unfortunately, I don’t know how much of what I heard yesterday is safe to share with the world. Having been scolded before for sharing too much here I will just say that it’s really exciting to see all the pieces of the puzzle coming together.
Today, and for the rest of the week, everything is fair game to share with you, so I will do my best! Emily Lakdawalla will also be blogging parts of the meeting, so I’ll also point you to her posts about the meeting as they go up. In fact, you should go check out her introductory post right now. You might also want to refresh your memory about the four sites by reading this summary.
Today started off with some overview talks from the project manager Mike Watkins and project scientist John Grotzinger. Mike showed some awesome pictures of MSL (aka Curiosity), which is really starting to look like a rover. A jaw-droppingly huge rover. Watkins also had some nice analogies to go along with his pictures to convey just how huge Curiosity is. Remember the little Sojourner rover? It could just about use MSL’s wheels like hamster wheels. MSL is also really tall: its mast cameras could look Shaq straight in the eye, and its gigantic arm is so long it could almost dunk!
I’m going to cheat and share a little of what I heard yesterday because this arm is just amazing and they used another good analogy. The instrument package at the end of the arm is huge: about 35 kg. You can picture this as something the size and weight of a lawn mower mounted on the end of a seven foot arm. The arm itself weighs 70 kg, and it is strong enough to dead lift that lawnmower even when the arm is fully extended. The MER rovers weigh 172 kg, the MSL arm weighs 105 kg. It. Is. Huge.
It finally sank in when I saw the presentations yesterday and today just how massive this rover is.
Anyway, back to today’s presentations. After the introduction, there were a series of talks about the preservation of biosignatures. One of the main take home points from these was that context is critically important for detecting and understanding biosignatures. If you understand the geology, you can try to look in places that maximize your chances of finding something. And then if you do find something, you can draw much better conclusions if you know its environment. This sort of argument makes a site like Eberswalde, where the story of a delta deposit in a crater lake is pretty well understood much more appealing than a site like Mawrth, where there are beautiful minerals, but we don’t really know the geologic story. Gale and Holden are both somewhere in between.
After biosignatures, there was a set of presentations about the mineralogy of the landing sites. This started with Frank Seelos unveiling the new and improved website containing a set of CRISM spectral images of the landing sites. You should go check them out: he specifically said that he would love it if we all melted his servers!
We also heard from Selby Cull, a graduate student who is attempting to use detailed models to figure out how much of a given mineral is in a sample based on its spectrum. Although it sounds straightforward, this is actually a phenomenally complex problem that planetary scientists have been grappling with for decades. It would be awesome if we could do this, but I’m skeptical.
After Selby, Ray Arvidson gave a talk about tying orbital to surface data at the MER Opportunity landing site and lessons learned that MSL should keep in mind. Bottom line (paraphrased) is that wherever you go, Mars is going to be more surprising and more interesting than we can imagine!
Finally Ralph Milliken shared his results on the compositions of the landing sites based on CRISM observations. It turns out that, using a subtle spectral parameter, you can estimate whether a given clay mineral detection is more or less “evolved” (where evolution could be due to burial or impacts among other things). Ralph also showed some exciting new stuff at Gale crater, including an example of a set of minerals visible in the southeastern portion of the Gale crater mound that looks very similar to the stack of mineral signatures seen near the landing ellipse.
Finally, after the mineralogy talks were over, we started hearing presentations about the specific landing sites. Gale was up first, and after Ken Edgett summarized the crater’s global and regional context along with some of what you can see within the crater, I gave my presentation showing off the interesting stuff that can be accessed in the ellipse and on a notional traverse up the lower portion of the mound. After me, my adviser Jim Bell presented about the composition of the stuff at Gale, and then finally Dawn Sumner gave a really interesting presentation about how to test some of our hypotheses at Gale Crater.
In the discussion of Gale the inevitable questions came up. One was: how old is the mound? The “problem” with answering that is that we think most of the terrain at Gale was buried and has since been exhumed again. That can totally throw off your estimated ages based on crater counting. The properties of the surface matter can too: some surfaces are hard and erosion resistant, so they tend to have more small craters than adjacent surfaces even if they are younger.The best estimate is that Gale crater formed at the end of the “noachian” period of martian history and the mound formed sometime in the late noachian to early hesperian. The exact timing of these epochs isn’t all that well constrained, but the noachian ended around 3.8 to 3.5 billion years ago, and it’s fair to say that Gale and its mound are about that old.
We also talked about what it might mean if the whole mound is wind-blown grains. It’s certainly possible, but very difficult to tell from orbit. If the grains just filled up a dry crater, that might not be so good for habitability, but the mound is carved by canyons so we know there was flowing water well after the mound material had been deposited and turned to rock. On the other end of the spectrum, the mound might all be wind-blown grains, but those could have been trapped in the crater because it was full of water. As we heard earlier in the day, fresh basaltic sand plus water would provide the chemical energy necessary to support a pretty impressive chemolithoautotrophic (aka rock-eating) biomass.
There was also a lot of discussion of the evidence that Gale was actually buried. Someone asked whether there are any patches of layered material on the crater wall that match the mound layers. There aren’t, but I pointed out that there is a nice outlier of layered material hidden in the dune field 20km west of the mound itself. Ken Edgett reminded people (as he has been doing for 10+ years) that “this isn’t the mars you’re used to thinking about”, that entire regions have been buried and exhumed, and that this can happen without leaving a trace on the underlying surface. He also pointed to Henry crater as a Gale-sized example that does have a mound that matches with material on the walls. The question of why Gale seems to have preserved its huge mound of sediment, but all the other craters nearby did not keep theirs came up, and John Grant suggested that we do crater counting on the nearby craters which we know are older than Gale to see if their surfaces are anomalously young – as if they had been buried for a few billion years.
I also got the question of whether we should try to visit all of the cool stuff that I showed in the landing ellipse if the true goal of the mission is the mound. This is going to be the core question for this mission. At all the sites but Mawrth, you land on cool stuff but your main goal is outside the landing ellipse. The tradeoff between doing the “safe science” right away in the ellipse and sacrificing science early on to be able to make it to potentially more rewarding targets is going to be a huge part of the landing site discussion over the next few months. On Wednesday we are going to hear from some of the engineers and rover drivers about the engineering constraints on the mission, and then the Landing Site Working Group (a small subset of scientists that have been looking very closely at the landing site) will work with the rover drivers to identify the key targets at a given site and the key observations we want to make at those targets. From there, the engineers will come up with a set of potential traverses with detailed estimates of how long each will take. Since all of the sites are safe to land in, I think these estimates will play a major role in finally narrowing down to the final selection next spring.