Archive for the ‘MSL’ category

Gale Crater Geomorphology Paper – Published!

September 16, 2010

Big news folks! The huge paper that I’ve been working on for the last couple years is finally, unbelievably, published! Even better for you, it is published at the Mars journal, which is an open-access journal. Just head on over and you can download all 53 pages of pure, distilled Science!

In case you don’t want to wade through that many pages (and almost as many figures) of Mars geomorphology jargon, I’ll summarize here.

Gale Crater is a large (155 km diameter) crater that sits just south of the martian equator on the boundary between the rugged, cratered highlands to the south and the smooth plains of the northern hemisphere. Gale is special because it’s not just a big hole in the ground: in the middle of the crater is a vast mountain of layered rocks that towers nearly 6 kilometers above the crater floor. As I’ve mentioned before on this blog, geologists love layers, because they are formed in the rock record when something changes. So the Gale Crater mound is a giant record of the changes that have taken place on Mars since the crater formed3 or 4 billion years ago. This fascinating stratigraphic section has evidence of water-bearing minerals like clays and sulfates, and the detections of these minerals seem to follow certain layers, so the hope is that those layers were deposited during a time when Mars was more habitable. That’s why Gale Crater is one of the four finalist landing sites for Mars Science Laboratory!

Even though a lot of people knew that Gale had this interesting mound, not a lot of work had been done on the crater, so in an effort to help the Mars community learn all we can about the geology of this possible landing site before making the decision whether or not to land there, I dove into the image data for Gale crater. I started with the Context Camera (CTX), making a huge mosaic covering the whole crater. I used that mosaic to map out easy-to-map features like sand dunes and branching channel networks.This was scientifically useful because it shows that there are lots of channels formed by water flowing into the crater, but it was also a good way for me to learn to use the mapping software ArcGIS.

After that, I spent a while working on determining the orientation of the layers in the mound using a digital elevation model based on CTX images. This work was also educational, but ultimately after showing it to several colleagues I found it was drawing criticism and wasn’t telling us a lot about the mound, so that was cut from the final paper.

I moved on and pored over the various HiRISE images of the potential landing site and the mound, identifying “units” based on their appearance in HiRISE, supplemented with CTX, thermal inertia data from THEMIS, and spectral data from CRISM. In doing so, I was able to put together a more detailed picture of what a rover might encounter if it landed on the crater floor and drove up the mound.

Three examples of inverted channels in the proposed MSL landing ellipse.

The landing site is centered on a fan of material that extends from the northwestern wall of the crater and ends a few kilometers from the base of the mound. Looking closely at the fan, it turns out that about two thirds of it is mantled with what looks like dust or soil, but the final third, closest to the mound, has been stripped bare, exposing a bunch of fractured layered rock. That’s interesting in an of itself, but the fan isn’t the only thing in the landing ellipse. I also found some examples of inverted channels: riverbeds that were resistant to erosion and ended up as mesas when the surrounding land was stripped away. There are also patches of a unit that I called the “mound-skirting unit” within the ellipse.

This mound-skirting unit is found all around the crater and tends to be erosion resistant, forming mesas. It also looks like it might be related to flowing water in some places: chains of mesas made of this unit extend across the floor from channels and fans on the crater wall. But elsewhere, there are parallel ridges in the mound-skirting unit that might be the remnants of ancient dunes that were petrified. One notable patch of the mound-skirting unit is partway up on the northwest side of the mound, right at the end of a channel that was carved into the layers of the mound and later filled with debris. This has been referred to as a fan, and if I had just looked at it without context I would have called it a fan too! But it has almost the exact same texture as the mound skirting unit nearby. My interpretation for this was that the original fan is mostly eroded away, but because there was a fan sitting on top of the mound skirting unit in this spot, it was protected from erosion so it remains as a mesa at the end of the filled channel.

Examples of erosion-resistant ridges on the Gale mound that might be due to water percolating through the rocks.

Another interesting thing that I noted about the surface of the lower mound is that there are cracks all over the place that look like they are resisting erosion, becoming lattices of ridges. This could happen if water was flowing through the rocks, cementing the material near the fractures and making them last longer than the un-cemented surrounding rock. These fractures occur in a part of the mound that shows hydrated sulfate signatures in CRISM, so there is some supporting evidence that water was involved.

I also looked at some of the material near the top of the mound, far beyond where MSL is likely to reach even with multiple extended missions, and I’m really glad I did. One of the big questions about the Gale mound is what type of rocks it is made of. It’s a lot nicer for habitability if you can say for sure that rocks formed in a lakebed instead of a desert, but it’s frustratingly difficult to tell the difference with orbital data. The upper part of the Gale mound might be an exception though: If you look really carefully, in some of the HiRISE images there is a strange “swirly” looking pattern that I interpreted as a cross-section through ancient sand dunes. If true (and there are certainly other possible explanations), this tells us that the upper mound was once a location where sand collected to form dunes, meaning it was probably a low point rather than a high point.

Examples of the weird texture in the upper mound that might be evidence that these rocks were once sand dunes.

The idea that Gale has been buried isn’t a new one, and after looking at the geology of the mound, I think it has actually been buried and unburied several times. The lower layers of the mound have deep gorges carved into them and craters on the surface, suggesting that they’re old, and that they were already eroded into a mound back when water was eroding things on mars. Above the lower mound is the upper mound, which looks like it was deposited separately, possibly much later. There is a channel in the lower mound that disappears beneath the upper mound to mark the “unconformity” between these two units. This means that just because I found what I think are petrified dunes in the upper mound, the lower mound isn’t necessarily the same stuff.

There’s lots more in the paper, but those are some of the key points. In a couple weeks I’ll be presenting at the MSL Landing Site workshop, where people who have been studying the four potential landing sites will share their results and the whole Mars community will argue and try to decide which site we should land at. These meetings are always exciting, and I’ll do my best to blog about the meeting here. The final decision won’t happen at the upcoming meeting, but it will be interesting to see if any sort of consensus starts to form. (don’t hold your breath!)


Jaded by Mars Organics

September 11, 2010

So, you may have heard the news making the rounds last week that a new analysis of the Viking data suggests there may actually be organics and (dare I even say it?) life on mars! Yawn. Consider me underwhelmed.

The gist of the story is this: A long-standing mystery in Mars science has been why the Viking instruments were unable to detect any organic molecules on Mars, not even at a level that would put Mars on par with the moon. Now, 30 years later, the Phoenix lander discovered the perchlorate molecule in the arctic martian soil. Perchlorate is a powerful oxidizer, and by heating a soil sample containing organics and perchlorate, you’re bound to destroy the organics. So, if there were perchlorates at the Viking site, then maybe the Viking instruments destroyed the very organics they were trying to find! The few traces of organic compounds detected by Viking were interpreted as residue from the chemicals used to clean the instrument, but the new results show that organics oxidized by perchlorate can also form those compounds.

To me, this sounds pretty familiar. See, as I understand it, the leading theory for what happened to the organics on Mars to bring them to levels below the moon is that some unknown oxidizing agent had destroyed the organics. So, now we know what the oxidizing agent might be, but it seems that the prevailing theory still holds. I suppose the excitement comes from the possibility that the organics could remain intact until the soil is heated, and so low-temperature investigations might detect them. But the modeling in the paper did not consider that the organics were sitting at the Martian surface for perhaps billions of years. Yes, heating in the oven might destroy the organics, but that may be meaningless if they were all broken down millions of years ago by UV radiation. As for the traces of organics that Viking did detect, as the press release mentions, they had the same Cl isotope ratio as Earth. Now, it’s not impossible that Mars has the same ratio as Earth, but it would be a coincidence. Invoking coincidences in science makes me uncomfortable.

A few years back, during my summer internship at NASA Academy, I earned the nickname “aguafiestas” which translates to “that guy who ruins all our fun”.  I earned the nickname for debunking some internet hoax emails that my friends were sending around, but it’s a nickname I wear proudly.

So, maybe I’m being an aguafiestas again with this press release, but I just can’t get that excited about the announcement. I will say that I am really looking forward to the results from the SAM instrument on MSL, which should be powerful enough to detect organics wherever they are hiding on the Martian surface. I’m not naive enough to claim that it will answer all our questions, but it might. Even an aguafiestas can hope!

Molar Tooth Texture

August 12, 2010

Ok, so remember the weird rock I showed in my Galcier Park geology post? No? Here it is again:

This texture is called “molar-tooth” texture, because apparently someone thought it looked like the teeth of elephants. They must have been studying some weird elephants. It’s a very bizarre texture. It cuts across the layers of the rock as if it is related to fractures, but it is often deformed and squished as if it formed in wet sediment. In some places the minerals filling the fractures are broken up and collected as hard clasts, but it other places they clearly formed after the sediment was deformed.

The two leading explanations for this texture are bubbles and waves*. In the bubble model, the fractures form when gas is evolved in the gooey mud, and builds up enough pressure to propagate through the layers. Then once those voids are formed, fine-grained crystals fill them in. Sometimes, the overlying pressure of newer sediment compressed the voids before they are filled, causing them to accordion up into the contorted shapes we see today. In the wave scenario, pressure changes from powerful storm waves cause the sea floor to undulate, forming the fractures which are then filled in with minerals.

This texture has no modern-day analog because macroscopic life forms disrupt the mud before the mineralization can take place.It’s very unlikely that we would find this on Mars, but it is good practice for us martians to try to explain rocks we’ve never seen before!

*I’m sure I am completely oversimplifying, and likely mangling, these explanations.

The Geology of Glacier National Park: Part 1

August 7, 2010

Well, the field trip is over and I am happy to say that I was not eaten by any bears. They seemed much more interested in the huckleberries.

My adviser and two colleagues and a family of bears.

I am also happy to say that I know a little bit more about the geology of Glacier National Park (and about how to interpret sedimentary geology in general) than I did before I left. The park is famous for its large-scale geography of course: towering mountains and deep valleys carved by rivers of ice. Glaciers tend to form broad U-shaped valleys, while rivers and streams cut V-shaped valleys. Take a look at this picture and you can see glaciers have been involved, even though they are mostly gone now (and the few that remain are disappearing fast: there will be no more glaciers in the park by 2030).

Glacier National Park: soon to be known as "U-shaped Valley National Park".

Despite the spectacular views, we actually spent most of our time in the park with our backs to the vistas, staring intently at rocks that most visitors would pass by without a second glance. Most of the rocks in Glacier are Precambrian sedimentary rocks, deposited around 1.5 billion years ago. The world was a very different place back then, with essentially no oxygen in the atmosphere and no multicellular life. Without large life forms crawling around in the mud of the seafloor (a process called “bioturbation”), the physical processes that shape the sediments are nicely preserved, and I learned a lot about how to interpret their record.

For example, take a look at this ripple:

This symmetric ripple indicates back-and-forth flow of water over the soft mud.

A ripple means that the water was flowing and moving sediment, but you can actually learn more than that based on its shape. This ripple is symmetric, meaning that the water was flowing back and forth, rather than only in one direction. That tells us that it didn’t form in a stream, but more likely due to the movement of tides or waves.

Here’s another interesting feature:

You can see that the layers here aren’t parallel – there’s a lens of material with a relatively flat top, but a curved lower portion that cuts into the underlying layers. This is a little channel, carved into the lower sediments while they were still soft and filled with coarser material!

The coarseness of the sediment tells you a lot about the environment where it was dropped. It takes a much faster, more energetic flow to carry rocks than it does to carry sand. Silt and mud will stay suspended in all but the most tranquil of bodies of water, so what happened here?

This location is actually much younger cretaceous rock outside the park, where the ancient Precambrian mountains have been broken down and deposited in a floodplain. (lots of dinosaur bones have been discovered in other outcrops of this cretaceous rock, but alas, we didn’t find any) There has been some crazy deformation in this area, tilting the layers so that they are almost vertical, but you can still see striking evidence of different environments here. This spot actually shows another much larger example of a channel, filled with big green and red rocks. (The channel is the coarse layer behind the geologist in the picture that narrows as you go upward) The size of the rocks in this channel means the water must have been flowing pretty fast to move them. But you can see that other parts of the same outcrop are very different. The tan stuff is extremely soft, and when you crush it between your fingertips, it turns into a powder with grains far too small to see or feel.

This soft stuff could have been emplaced when the river carrying the larger rocks flooded its banks, dumping its sediment as it stagnated in the floodplains. This same process is why places like the Nile river valley are so fertile. It’s not a sure thing that the fine-grained stuff came from a flooding river though. It could also be fine ash from a volcanic eruption (a more likely scenario for Mars!).

There’s a lot more cool geology to show you from the park, but this post is long enough, so I will leave you with a puzzle. Take a look at this bizarre rock texture that we saw all over the park:

What is going on here?

What do you think it is? We were asked the exact same question by our field trip leader to get us to practice explaining completely unknown rock types, something that could very well happen on Mars. Stay tuned for my next post where I’ll attempt to explain what this texture is!

Is Eberswalde Really a Smoking Gun?

August 3, 2010

The other day in Mars journal club, we took a look at a paper about the “fan” in Eberswalde crater. You may recognize this name: it is one of the four finalist landing sites for MSL. The site was chosen because at the western end of the crater, there is a feature that most Mars scientists consider to be a delta, formed when sediment transported by rivers  encountered standing water and settled out.

The paper we looked at considered an alternative to the delta hypothesis. Instead, Jerolmack et al. proposed that the fan could be an alluvial fan, formed by river channels that “avulsed” back and forth to form a gradually sloping fan. “Avulsed” means that the river abruptly changes its course. When you average out over lots of avulsions, you get a broad, shallow cone of material deposited: an alluvial fan.

Jerolmack used a computer model of this style of fan formation and fit it to the slope of the Eberswalde feature’s surface. They found that, if the Eberswalde fan is actually alluvial, it would have formerly extended about 40 km out into the crater, and that it could have formed extremely rapidly: in tens to hundreds of years, and with no need for a standing body of water.

That’s a much different story than the more popular one: that the Eberswalde fan is a delta that formed over many thousands of years in a lake. Which scenario is correct? I don’t know. It may not be possible to know from orbit. That’s part of why Eberswalde is a candidate MSL landing site: if our “smoking gun” evidence of a lake on Mars turns out to be an alluvial fan deposited in 50 years, then that certainly has an influence on the question of the habitability of Mars as a whole! Of course, everyone hopes that it is truly a delta, in which case it would have been favorable for preserving organic biomarkers and would record a lot of information about the martian environment.

There’s only one way to know for sure: land there!

ResearchBlogging.orgJerolmack, D. (2004). A minimum time for the formation of Holden Northeast fan, Mars Geophysical Research Letters, 31 (21) DOI: 10.1029/2004GL021326

Big Sky Country

July 31, 2010

Well folks, I’m headed off to Big Sky Country tomorrow (aka Montana)! I’ll start the week at the MSL camera team meeting, where I will get all sorts of cool news about the MastCam, MAHLI and MARDI cameras which I will not be able to share with you.* After that, the lot of us will pack up and head to Glacier National Park to learn about the geology of the Belt-Purcell supergroup, and more generally, how to apply terrestrial geology to martian geology. I always enjoy field trips like this because I get to hike around on the rocks with a bunch of experts as well as many with less field experience, so there are lots of educational discussions. Also, did I mention the part where I get to drive and  hike around in spectacular scenery? Yeah. Times like this I’m reminded that my job Does Not Suck.

I’ll try to write a post or two about the trip once I actually understand the geology we’re going to see a little more. Hopefully the weather will cooperate and I’ll have some pretty pictures to share too!

*One of the difficulties with actually being involved in missions is that I can’t just write about all the cool stuff I hear about. I got scolded when this blog was just starting out for posting information before JPL or NASA had approved of it, so I tend to err on the side of caution now. It’s frustrating, but there’s nothing I can really do.

MSL Roves!

July 27, 2010

I’m a little late on this, but I thought I should share the news: MSL now has a good head and neck on its shoulders, and has officially “roved”. Last week, engineers at JPL installed the “Remote Sensing Mast”, bringing MSL’s total height up to nearly seven feet tall (2 meters). Also, MSL drove for the first time in the clean-room where it is being assembled! Here is a 3D photo of the rover just prior to driving, taken by Kris Capraro:

And then, to celebrate the momentous occasional, one of the JPL engineers busted out the dance moves. Specifically, The Robot: