The 4th MSL Landing Site Workshop

Posted September 24, 2010 by Ryan
Categories: Astrobiology, Clays, Craters, Curiosity, Current Research, MSL, NASA, Ryan's Research, Sulfates, Water on Mars

Tags: , , , , , , ,

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.

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Meteorite Ahead!

Posted September 21, 2010 by Ryan
Categories: MER, NASA, Opportunity

There has been a flurry of emails going around among the MER team about a certain rock ahead of the Opportunity rover that looks like it may be yet another meteorite.  It certainly doesn’t look much like the local meridiani rocks, which are the light-toned patches in the photo above. Meteorites are interesting because they provide information about the weathering environment on mars. We know that Mars is all rusty, but iron meteorites are nice and fresh when they fall, so by studying how rusted they are we can learn about the martian atmosphere.

Another thing that strikes me in the photo above is how close Endeavor’s rim looks! I’ve been a bad martian and haven’t looked at the photos from Opportunity for a while, so it’s great to see those distant hills looking not-so-distant. Of course, they’re still a long way off, they’re just really big. It’s like driving toward a mountain range here on earth. You can see your destination long before you get there, and then it seems to taunt you as you creep closer and closer.

For more information about the meteorite sighting, check the NASA press release.

The Science of Starcraft: Supernovae and Gauss Rifles

Posted September 21, 2010 by Ryan
Categories: Astronomy, Fun Stuff, Science Fiction, Science of Starcraft

I’ve got two new posts up at The Science of Starcraft! The first tackles the difference between supernovae and novae. The words are often used interchangeably in sci-fi, but they are (usually) very different phenomena. Plus, I love telling the story of nucleosynthesis and stellar evolution, and this was a good excuse.

The second post is sort of a sequel to my previous post about railguns. This time I look at gauss rifles, another electromagnetic futuristic weapon that pops up in sci-fi pretty often, but is incorrectly depicted in Starcraft:

Gale Crater Geomorphology Paper – Published!

Posted September 16, 2010 by Ryan
Categories: Curiosity, Current Research, MSL, NASA, Ryan's Research, Water on Mars

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!)

Carnival of Space #169

Posted September 12, 2010 by Ryan
Categories: Carnival of Space

Hey everyone, the 169th Carnival of Space is up at Next Big Future! Go take a look. Now.

Jaded by Mars Organics

Posted September 11, 2010 by Ryan
Categories: Astrobiology, Current Research, MSL, Phoenix, Skepticism

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!

Donors Choose

Posted September 9, 2010 by Ryan
Categories: Uncategorized

Donors Choose is a charity organization that allows teachers to post requests for supplies that they can’t afford and allows donors to (get this!) choose which teachers to donate to. Some requests are for basic school supplies, others are for computers or video cameras or other big-ticket items that a teacher’s district can’t afford. It’s a great organization, and you should go check out the projects and donate to the most deserving.

But if I may suggest one to donate to, my wife is a physics teacher and she recently put in a request at Donors Choose for funding to buy motion detectors for her physics classes. She uses these in a bunch of different projects, and they are great for showing students how motion in the real world can be recorded as data on a graph. Making that connection – that graphs actually mean something – is a cornerstone of science, and she (and her students, and I) would be eternally grateful if you donated to her project. Thanks in advance!