Archive for the ‘Polar Geology’ category

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.

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Mars Art: Mind-blowing Swiss Cheese

November 6, 2009

First of all, a reminder to go vote on my article about MSL, which is a finalist in the scientificblogging.com science writing competition.

Ok, done? Good. I wanted you to do that before I showed you this image because it may very well break your brain. This is a HiRISE image of the so-called “swiss cheese” terrain at the south pole of mars. The terrain is formed by the sublimation of CO2 ice, which forms weird rounded pits. Yes, the round things in this picture are pits.The smooth parts are mesas and the illumination is from the lower right. Pictures like this always make my brain hurt because for some reason I want to see the round depressions as bulges! And if you think this is bad, try watching a scientific presentation with dozens of pictures like this, with varying orientations and illumination angles. I rarely get anything out of Mars south pole talks because my brain is so busy struggling to see the images properly.

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Believe it or not, illumination is from the lower right in this image. Click the image to go to the HiRISE page and check out the full sized versions.

Surreal-looking HiRISE Picture of the Day

June 25, 2009

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I don’t have time to write a full post since I am busy trying to get a presentable outline of my PhD thesis prepared to show to my committee next week. So in the mean time, enjoy this beautiful and bizarre HiRISE image of defrosting terrain on Mars. Click the image or this link to go to the HiRISE page and see the full version.

LPSC 2009: Day 2

March 28, 2009

Day 2 was all about ice in the mars sessions: the morning focused onĀ  the polar caps and the afternoon focused on the subsurface. I also managed to catch a few non-mars talks.

One of the first talks I saw was by Ken Tanaka, famed for his geologic maps of Mars. He showed the results of his studies of the north polar cap, and identified at least two major hiatuses. The official geologic definition of hiatus is: “A cessation in deposition of sediments during which no strata form or an erosional surface forms on the underlying strata; a gap in the rock record.” Tanaka showed examples of locations that demonstrate the different ages of layers, but the main take-home message of his talk was that most of the time, things are not being deposited on the polar cap.

HiRISE color view of defrosting sand dunes. The dark streaks are locations where the ice is gone and the dark sand grains are able to blow across the icy dune surface.

HiRISE color view of defrosting sand dunes. The dark streaks are locations where the ice is gone and the dark sand grains are able to blow across the icy dune surface.

Ken Herkenhoff gave an interesting presentation about HiRISE observations of active processes at the poles. He emphasized that there are many processes that they will understand better after another year of repeated observations, but still had some interesting results. He talked about active streaks in gullies and the strange fans and spots that form on defrosting dunes. Interestingly, these spots tend not to form on the base suface beneath the dines, implying that the material underneath the ice has to be mobile enough to blow around once the ice is partially removed.

HiRISE also observed avalanches in action on the north polar cap! As ice begins to thaw in the spring, debris from the ice cap can come loose and cause an avalanche. These are apparently pretty common, because multiple avalanches were actually caught in action in the same image!

An avalanche in the Martian arctic caught in action.

An avalanche in the Martian arctic caught in action.

Finally, Herkenhoff showed a picture that apparently has everyone baffled. There are lots of streaks seen on the polar cap, but some like the ones in the following image don’t make much sense. It looks like most of the streaks in the image are going down-slope, so you might think they were formed by small avalanches of dust or something. But why do they have such sharp edges? And, more importantly, why are some of them diagonal compared to the rest?!

Strange streaks on the north polar cap. Nobody knowsh why these have such sharp edges, or why one of them is diagonal.

Strange streaks on the north polar cap. Nobody knows why these have such sharp edges, or why some of them are diagonal.

I darted out of the Mars talks just in time to catch an interesting Enceladus presentation by Sue Kieffer. She took a look at the thermodynamics of warm ice in a vaccum and believes that the ratio of ice to water vapor in Enceladus’ famous plumes is half of what was originally reported. Kieffer claimed that the original calculation made a faulty asumption about the range of particle sizes in the plume, which led to a very different estimate. Why is this a big deal? Because it turns out that Kieffer’s calculations fit much better to sublimation than boiling liquid water! Enceladus might not have liquid water at its pole, it might just have warm ice! I’m sure the icy moons community will be looking into this some more and trying to figure out which calculation is correct as soon as possible. It would be really cool if we could prove that there’s liquid water on Enceladus, but the universe doesn’t care what we think is cool, so maybe the little moon is just a warm ice-ball.

The plume of ice and vapor coming from Enceladus' south pole has caused quite a stir, but one talk this year suggested that it could be formed without any liquid water.

The plume of ice and vapor coming from Enceladus' south pole has caused quite a stir, but one talk this year suggested that it could be formed without any liquid water.

Finally, I saw Steve Wood give a really interesting talk in the afternoon about atmospheric collapse on Mars and its effects. Mars’ tilt changes over millions of years, and occasionally it decreases to the point that the global temperatures drop, and CO2 from the atmosphere is dumped on the surface in a thick layer. This talk considered what that blanket of CO2 would do the the martian subsurface and concluded that it would indeed act as a blanket. CO2 ice has a lower thermal conductivity than rock, so the ice and icy soil would act to trap the geothermal heat of the planet, and might cause a subsurface warming of 20 degrees: enough to melt ground ice and drive off the water from some hydrated minerals. This is a really interesting effect and I had never heard of it before!

The MOC Book: Polar Processes

February 28, 2009

I’m falling behind on my blogging of the MOC “book”! We read a lot this week, so I will just stick to the highlights. In other words: mostly pictures, less text. This paper is really all about the pictures anyway! (if you’re just tuning in to the MOC series, check out posts 1,2,3 and 4)

The Martian poles are extremely fascinating but extremely bizarre places. The polar caps are made of water and CO2 ice, and as that ice freezes and thaws, it forms some strange landscapes.

a) South polar "swiss cheese" terrain, formed by sublimating CO2 ice. b) North polar pitted terrain. It is not clear why the north and south pole look so different.

a) South polar "swiss cheese" terrain, formed by sublimating CO2 ice. b) North polar pitted terrain. It is not clear why the north and south pole look so different.

The north and south polar caps are very different-looking, and there is no good explanation for why. This image shows layers from the south and north polar cap. The southern layers are very rough and rugged-looking, while the north polar layers are much smoother.

a) Rough, rugged layers in the south polar cap; b) Very smooth layers in the north polar cap. These layers may reflect changes in the Martian climate driven by changes in the planet's tilt and orbital eccentricity.

a) Rough, rugged layers in the south polar cap; b) Very smooth layers in the north polar cap. These layers may reflect changes in the Martian climate driven by changes in the planet's tilt and orbital eccentricity.

The layers in the north polar cap are amazingly coherent. They can be traced for hundreds of kilometers in some places:

Layers in the north polar cap can be traced for hundreds of kilometers. Prior to MOC, it was thought that the polar cap layers were tens of meters thick, and could be explained solely by changed in the planet's tilt. The fact that these layers are so narrow indicates that there are higher-frequency changes contributing to layer formation.

Layers in the north polar cap can be traced for hundreds of kilometers. Prior to MOC, it was thought that the polar cap layers were tens of meters thick, and could be explained solely by changed in the planet's tilt. The fact that these layers are so narrow indicates that there are higher-frequency changes contributing to layer formation.

Not all of the polar layers are perfectly flat, though. There are some examples of layers that have been deformed, or which intersect with each other, implying that they were subject to tectonics and erosion between periods of deposition.

a) An "angular unconformity", implying that enough time elapsed for some of the layers to become tilted and eroded before the next set were depositied. b) Deformation implies that these layers have a complex history as well.

a) An "angular unconformity", implying that enough time elapsed for some of the layers to become tilted and eroded before the next set were depositied. b) Deformation implies that these layers have a complex history as well.

The paper had a lot of observations, but not many conclusions about the Martian poles. The poles are still not well understood, though missions like Phoenix and MRO are helping to shed some light on the mysterious processes that shape the polar regions.

Mars Art Galleries!

November 10, 2008

Apparently I am not the only person who has had the idea of posting “artistic” images of Mars! In the past week I’ve come across two sites with collections of Mars Art images. So in lieu of posting my own image this week, I’ll point you to these sites who had the idea before me!

First is a site by Jim Plaxco called simply the Mars Art Gallery. It has lots of images, both unaltered and false-colored. He tends to manipulate the images a bit much for my tastes, but some of the results are pretty cool. Unfortunately it doesn’t look like the site had been updated recently. Here are a few samples:

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Dunes in Proctor Crater

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A view of the south polar residual cap “swiss cheese terrain” in a strange color scheme.

The second site is a very nice NASA site that I can’t believe I had never seen before! It is a treasure trove of beautiful mars images in both greyscale and false color form orbiters and the rovers. Here are a couple of examples, but you really should go check out the whole gallery. I’ve got my work cut out for me in later Mars Art posts to beat this site’s gallery!

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Granule ripples at Meridiani, as seen by the Opportunity rover.

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A false color view of the Meridiani region a few hundred kilometers north of the Opportunity landing site. Red indicates warm rocks, while blue indicates cooler sand or dust.

Mars Art: Linear Dunes near the North Pole

October 28, 2008

I am starting a new thing. Every week, I will browse through data from current and past Mars missions and find an “artistic” image to post here. I’ll talk briefly about what the image says scientifically, but mostly this is about eye-candy and the crossover between science and art, which I have talked about before. Without further ado, here’s your first piece of “Mars Art”:

This image is a HiRISE view of linear dunes near the Martian north pole. The shape of the dunes themselves indicates that winds in this area tend to vary, first blowing along the dunes from one side, then the other, but always in a generally west-southwest direction. Between the dunes, the bare ground shows polygonal cracks similar to the ones that Phoenix landed on. These cracks are a good indicator of permafrost in the soil. Click for a higher resolution jpeg, or go to the HiRISE site to learn more about the image or to look at the full-resolution version.