Archive for the ‘Sulfates’ category

4th MSL Landing Site Workshop: Day 1

September 28, 2010

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!

Curiosity is a huge machine. Note that the giant blob of instruments are not yet mounted on the arm in this photo.

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!

An example CRISM map of part of the Mawrth Vallis landing site, showing off the spectacular hydrated minerals in the site.

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.

A colorful map of the mineralogy at Gale Crater from Ralph Milliken. Greens are phyllosilicates, blue and magenta are sulfates, red is olivine, and orange is mixed sulfates and clays. The landing site is at the top center of this image, and the rover would ideally drive to the northwestern part of the mound, where there is lots of CRISM coverage.

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.

Three views of Gale crater. Top: An HRSC topographic map of the crater. Middle: A THEMIS thermal inertia map of the crater. Brighter areas are rockier, darker areas are dustier. Bottom: A THEMIS "decorrelation stretch" map, showing variations in color that can be roughly tied to composition. Pink is olivine, blue is dusty. Source: Anderson and Bell (2010)

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.

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The 4th MSL Landing Site Workshop

September 24, 2010

Well folks, I’m off to Pasadena to help the Mars community decide where to send its next rover. Long-time readers will recall that i’ve been to a couple of these things before and they’re always fascinating. I was going to post a reminder of what the four finalist sites are, with pros and cons and all that, but it turns out I don’t have to! My friend Lisa Grossman, a former Cornell astronomy major, is now a science writer for Wired! She interviewed me and my adviser earlier this week and put together a nice article summarizing the sites. I’m quoted in it quite a bit, so rather than repeat the same stuff, I’ll just point you over to her piece.

There are a few points of clarification that I should mention. First, the article says that MSL is searching for life, and that’s not really true. MSL is searching for signs of habitability. Obviously finding life would be a pretty good sign! But habitability is broader than just the search for life or even the search for organic molecules. Evidence for habitability could come from the texture of a certain rock telling us that it was deposited in water, or from the detailed chemistry revealing that the minerals in the rock could only form in benign liquid water.

Also, she’s right that some of the clays at Mawrth are kaolinites, which tend to form on earth in tropical soils. But to clarify, I don’t think anyone is saying that the huge amount of kaolinite clays at Mawrth are the result of tropical conditions. They do suggest that there was a lot of water involved though, which is why Mawrth is so interesting.

A final clarification: in the article, it mentions that it will take “several days of hard driving” to get to some of the go-to sites, where the really interesting stuff is outside the ellipse. If it were several days, that would be no big deal. It is going to be more like a year or two. A lot of people are really nervous about landing, only to have to buckle down and drive drive drive to get to the main target of the mission. Of course, all of the sites have good science to do in the landing ellipse, but that is a blessing and a curse for a go-to site. On the one hand, you get some results early on in the mission, but if you don’t have a lot of discipline, you can spend all your time staring at the rocks at your feet and never get to go climb the mountains in the distance.

With that, I’ll let you go read the article. You can also check out my old blog posts about the sites from the last time one of these workshops was held (Gale, Holden, Mawrth and Eberswalde). I’m going to do my best to take notes and blog about the meeting, and Emily Lakdawalla of the Planetary Society will be there for part of the meeting as well. We’ll do our best to keep you informed!

PS – You should totally check out the comments on the Wired article, where someone calls me out for saying that there was water on Mars and says that we Mars scientists are either stupid or have ulterior motives. Someone hasn’t been paying attention to every press release about mars for the past decade or so.

MarsSed 2010 Field trip – Day 1: Guadalupe Mountains and Evaporites

April 26, 2010

Hello everyone, I’m back from the MarsSed 2010 meeting in ElPaso! The meeting was great: it was small and focused on sedimentology and stratigraphy on Mars, with lots of room for discussion. Even better, there were plenty of terrestrial geologists attending, and their comments were extremely helpful for me, and probably many other Martians who lack a geology background.

After two and a half days of presentations and discussion (and a lot of learning on my part), we headed off on our field trip to the Guadalupe Mountains!

We started off in a salt flat graben with a lovely view of the Guadalupe mountains. What’s a graben, you say? It is a low-lying block of land, bordered by parallel faults. If you have heard of the “basin and range” region of the southwestern US, then the basins are graben. The mountain ranges are also called “horsts”.

A nice diagram of horsts and graben. This is how the "basin and range" area of the southwest formed.

The graben that we stopped in was a salt flat, where gypsum and halite are left behind when water collects in the lowlands and then dries out.

A view of the Guadalupe Mountains from the salt flat.

From our vantage point, we studied the nicely exposed mountains and compared them to a detailed cross-section of the area. The rocks of the mountains were once a large carbonate reef on a continental shelf. When sea level was high, thick carbonate beds were deposited on the slope of the continental shelf, and when sea level fell, sand and silt from the continent  were transported across the reef and deposited in the floor of the ocean basin. Here is a nice illustration that we found at one of the national park exhibits on the last day that really helped clear things up for me.

A diagram showing the relationship between the geographic setting and the underlying stratigraphy of the shelf and reef.

Here we are on the salt flat taking our first look at the stratigraphic cross section of the Guadalupe mountains. The mountains are off to the right, outside the field of view of this picture.

You may wonder what the relevance of ancient ocean reefs are for a bunch of Mars scientists. Fair enough. Nobody claims that we would find a big carbonate reef on Mars. Believe me, scientists have been searching for carbonates on Mars for decades. Recently, some small amounts have been detected, but nothing comparable to a huge reef. We were instead studying the reef as an example of a well-understood stratigraphy on Earth, and trying to learn how that stratigraphy was deduced. One of the main lessons was that not everything starts as a flat-lying layer! In fact, the edge of the reef appears to form a nearly horizontal layer, but it is actually made up of multiple sequences building outward into the basin. It just seems to form a layer because the reef always forms at the edge of the continental shelf. You can sort of see this “fake” layer in the pictures above. It is dark blue in the colorful cross section and is the light-toned band in cross section in the artist’s impression.

After discussing the cross section in some detail, and particularly admiring the large, inclined beds of the reef that were exposed in the mountains, we moved on to take a look at the deposits that filled the ancient Delaware basin when the sea began to dry out. The deposits have a very striking light and dark banding:

Layered evaporite deposits in the Castile Formation in the Delaware Basin. The light layers are gypsum, formed during the summer when evaporation rates were high, the dark layers are carbonate formed in the winter when evaporation was slower.

The light layers are gypsum and the dark layers are carbonate. The current theory is that each couplet represents one annual cycle: gypsum was deposited in the summer when evaporation was rapid, and carbonates were deposited in the winter. Apparently some poor graduate student counted all 260,000 couplets, which implies that it took about that many years to fill the basin with evaporites.

Something similar may have happened in the Mediterranean Sea more recently. It is thought that occasionally, the ocean level drops to the point where the Mediterranean is cut off from the Atlantic, and begins to dry out, depositing similar salts on its floor.

The relevance to Mars in this case is a lot more clear. There is evidence that many large craters were once filled with water. Now they are bone-dry, so presumably big evaporite deposits should be common on Mars! There are nice big stacks of hydrated sulfates at the bottom of Valles Marineris which might be remnants of such a deposit that precipitated out of a body of water in the canyon.

Stay tuned for Days 2 and 3 of the field trip! If you’re really interested, I suggest that you check out the awesome field guide that was made especially for our trip.

AGU 2009 – Day 1

December 16, 2009

For those not familiar with the conference, the fall meeting of the American Geophysical Union is a terrifyingly, overwhelmingly large conference. Each year, something like 16,000 geoscientists descend on San Francisco to share their work. It is also one of the major planetary science conferences, so a lot of new results are first presented here.

Moscone Center in San Francisco. This building is filled with science at every fall AGU meeting.

This year, the first talks that I checked out on Monday were about radar observations of Mars. By sending radar waves from spacecraft to the surface and then recieving the reflected waves, we can learn a lot about Mars. In particular, since radar penetrates tens to hundreds of meters below the visible surface, it can reveal otherwise hidden structures. This has been especially successful at mapping the structure of the polar caps, because radar penetrates through ice quite well.

Roger Phillips gave a talk summarizing some of the results from the SHARAD radar instrument on MRO. Among other thers, SHARAD has found evidence that the spiral troughs in the north polar ice cap have migrated over time, as predicted many years ago by theoretical models. SHARAD has also found ancient buried canyons in the polar ice, which menas the ice caps have been around for quite a while. There are also some exiting new results implying that the material filling valleys in the Deuteronilus Mensae area is quite transparent to radar waves, and might in fact be something like glacier ice.

Image credits: NASA/ESA/JPL-Caltech/ASI/University of Rome/University of Washington St. Louis

After the radar talks, there were a whole bunch of presentations about aqueous alteration on Mars. One of the main lessons that I took away from those talks was that Mars is still a very confusing place. For example, Hap McSween used data from the Mars rovers and characterized typical soils at both landing sites. He found that the compositions of soils are roughly 70% unaltered material and 30% alteration products. He also showed that the soil compositions are quite similar between the two landing sites, which are on opposite sides of the planet, and that the unaltered portion of the soil is similar to the rocks at both sites.

However, the next talk by Josh Bandfield used orbital data and found that in general rocks on Mars have more of the mineral olivine than the soils. This is a somewhat different result than the rover data, and it might imply that rocks on Mars actually have more magnesium and iron than previously thought.

Other talks related to Mars alteration focused on “clay” and sulfate minerals detected on Mars. One that I found particularly interesting was by Paul Niles, who pointed out that Mars is an “obliquity-driven” planet. In other words, its tilt varies widely, and the Mars we see now is not typical. Niles suggested that during more typical periods, ice might have formed large layers at Mawrth Vallis, a location known for its strong hydrated mineral features. Melting at the base of that ice could have leached the rocks, explaining the presence of specific Al-bearing clay minerals.

Map of water-bearing minerals at Mawrth Vallis. Image credit: ESA/OMEGA team

Another interesting talk was by Itav Halevy, who took a look at how the presence of SO2 gas influences the formation of carbonate minerals. It turns out, even a tiny amount of SO2 gas (which is often released by volcanoes) can prefent the formation of CaCO3. If there is iron around, FeCO3 (the mineral siderite) forms instead. The implication is that sulfur minerals should form in different locations than clay minerals and siderite.

Continuing with the sulfur theme, Albert Yen talked about some results from the Spirit rover. He said that basically, if the rover had to get stuck, it picked a really fascinating place to do it! Based on the compositions measured, it turns out that there is too much sulfur in the soil to balance it out by assuming it is combined with other elements like Fe and Mg. That means there might be pure elemental sulfur mixed in with the soil, which would be consistent with hydrothermal activity!

My officemate and occasional contributor here at the Martian Chronicles, Briony Horgan, also gave a nice talk summarizing some of her recent work. For a long time there has been a question about the so-called “surface type 2” on mars. This surface type has higher than usual Si, but that could be due to a different type of lava, or alteration of the more common basalt seen elsewhere on Mars. Briony presented new evidence, based on the overall shape of the spectra of surface type 2 regions, that these areas might be due to a silica glass coating! This sort of coating could form when thin films of water from thawing ground ice altered the surface of sand grains, and would imply relatively recent alteration processes on mars.

Finally, the day ended with the Whipple prize lecture, which was unfortunately full of some misleading information about the history and status of Mars science. But that’s the topic for a future post.

Massive Crystals: The coolest thing I’ve ever seen.

October 21, 2008

Really, that’s all I said for like 5 minutes after seeing this picture for the first time:

Those are PEOPLE, for scale. Here’s another pic, just to put you in a little more awe:

These are the largest crystals yet to be found on Earth, with some reaching over 30 feet in length! As reported in NG, The Cueva de los Cristales is located 1000 feet below ground in the Chihuahua desert, and was discovered in 2000 during drilling for a nearby lead and silver mine. The cave is excrutiatingly hot and humid – 112 degrees F and 90-100% humidity! The cave is so hot, that suiting up to go inside is sort of like doing a reverse space walk. Everyone has to wear ice packs, full body insulation, and a respirator mask in the cave.

The reason the cave is so hot is also part of the reason the crystals formed here. The cave lies above a magma resovoir, which heated the local groundwater. Until 1985, when the mining operation lowered the local water table to extend the mine, the cave was completely submerged in this super heated groundwater. As the magma cooled, the water in the cave cooled enough to deposit selenite, a form of gypsum. The environment in this cave was stable enough over hundreds of thousands of years that the selenite crystals were able to continue growing uninterrupted.

We know there are massive gypsum deposits on Mars (ref: my thesis!), and we know that Mars has been much more tectonically stable than the Earth, so who knows? We might find crystal deposits on Mars to dwarf Cueva de los Cristales. Everything’s bigger on Mars anyway, right?

MSL Workshop Presentations!

September 17, 2008

For those of you playing along at home, I thought I should point out that most of the presentations so far are posted at the “marsoweb” landing site website, so I encourage you to go check them out.

Also, in case you were wondering, I have no idea which sites I want to survive this process. I have one or two that I am skeptical of, but I am really glad that today we are not just voting for which sites that we want. What we will do is answer eleven questions about each site with green, yellow or red depending upon whether we this the site is good, ok, or bad in that regard. Then in the end, we just find the three with the most greens.

It is sure to be an interesting day, and I know that there are going to be some flaring tempers and heated discussions. I’ll post as soon as possible with the results. Stay tuned!

Potential MSL Site: South Meridiani

September 16, 2008

The south Meridiani landing site is a newcomer to the bunch. It was added earlier this summer as a replacement for the north meridiani site. The south Meridiani site is about 100 km due south of the Opportunity rover landing site and about 100 km due east of the Miyamoto site. What makes the south Meridiani site interesting is that, just south of the landing ellipse, you transition from Meridiani plains material to ancient, water-eroded hills containing phyllosilicates.

The site has good context, in that we would land on the same sort of material that Opportunity is studying. However, the context for the phyllosilicates in the hills is bsically zero. We don’t know where they came from or how they got there.

For diversity of mineralogy, the rocks in the ellipse are probably sulfate-bearing just like the ones Opportunity sees, and are also rich in hematite (probably more blueberries). South of the ellipse, the clays in the hills are pretty diverse, with different chemistries.

Habitability? Well, we are pretty sure the meridiani rocks were once soaked in groundwater, but that water may have been a very salty and acidic brine. We don’t really know about how the phyllosilicates got there, but if they were marine or lake sediments, that would be great for habitability. However, they could also be crater ejects, which is somewhat less good.

As far as preservation goes, both sulfates and phyllosilicates are good at preserving organics under some conditions, so you would have two different, but good chances to see preserved biomarkers.

The mission at south Meridiani would be three phases. Phase 1 would be landing on the meridiani plains and using the new tools on MSL to better understand the same general rocks that Opportunity has been studying. MSL would land in a place that is in lower layers than Opportunity, so would fill in some of the earlier story. Phase two would be driving south to the contact between the meridiani plains unit and the ancient clay-bearing hills. And phase three would be exploring the hills.

The discussion phase once again brough up some tough and important questions about the site. Someone asked whether, when we cross the boundary between the plains and the hills, we are seeing the transition between a sulfate-forming environment and a clay-forming environment, or are we just seeing “before and after” and missing that transition. Someone pointed out that even if there are “missing layers” due to some period of erosion or non-deposition, that still contains information, because the surface would be weathered and altered before the new rocks were laid on top.

Someone else pointed out that this is a perfect example of an interesting mineralogy site, but with no context. We don’t know the whole “source to sink: story of the phyllosilicates. It was compared with all of the interesting rocks that Spirit has seen in the Columbia Hills: all very cool, but hard to piece together into a story.

Another very important question was whether the clay-bearing rocks had any distinctive appearance. Because MSL will probably not be able to identify them from very far away. (at best, ChemCam, the laser, might be able to… that’s part of my future research, so we’ll see) There wasn’t a good answer to this, though the phyllosilicates are seen in somewhat diagnositc “fractured” rocks.

The bottom line is that this site would be interesting because we would learn more about Meridiani, and would be able to cross a transition and explore very old clay-bearing rocks. However, the context for those clays is pretty weak, and we might end up being totally confused due to that lack of context. This site does have the advantage that it is incredibly safe. Meridiani planum is FLAT. I don’t think it’s the best science site, but it is an acceptable science site, and it may end up surviving or being brought back later on because it is so easy to land on.