Archive for the ‘Hydration’ category

AGU 2009 – Day 3: Venus and the Moon

December 20, 2009

I’m splitting day 3 into two posts because there were so many interesting sessions. Stay tuned for the second post about astrobiology and society. But for now, Venus and the moon!

Image credit: Nick Anthony Fiorenza/NASA

I started the day off at the Venus session. One of the first talks I heard was by Cedric Gillman about the history of water on Venus. He suggested a very thick primordial H2O atmosphere with a surface pressure of 300 bars, eventually escaping until just 15 bars of O2 were left. That oxygen then was absorbed as it reacted with the rocks. Gillman cautioned that Venus’ evolution shows that you can have a very hostile environments but still have water and oxygen in the atmosphere; something that we should keep in mind when looking for “habitable” exoplanets.

The next two Venus talks described using two complementary laser-based techniques on a lander mission. Shiv Sharma showed that Raman spectroscopy, which uses laser pulses to characterize the molecules in a target, would work under Venus-like conditions for a variety of rock types. In the following talk, Sam Clegg showed that Laser-Induced Breakdown Spectroscopy (LIBS), which analyzes the elements in a sample by zapping it with a laser and collecting the spectrum emitted by the resulting plasma, would also work under Venus conditions. Sam is my main contact on the ChemCam team and allows me to use his laser lab for some of my work, so it was cool to see some of the other LIBS work that he does.

A sample being zapped by a LIBS laser.

Both Raman and LIBS are great for Venus because they are fast, capable of remotely analyzing a sample in seconds. When your probe is only going to live for an hour in the crushing pressure and deadly heat of Venus, every second counts, and these techniques could be extremely useful.

The final Venus talk that I heard was a status report on the Japanese Venus climate orbiter. They unveiled its new name: Akatsuki, which means “dawn” in Japanese, specifically the time of the morning when Venus is just visible as the morning star. Akatsuki is going through final thermal vacuum tests in January and will launch some time in 2010.

Artist's rendition of Akatsuki at Venus. Image credit: JAXA/Akihiro Ikeshita

Later that day, I stopped by the lunar dust session to hear a talk by Bonnie Cooper about the toxicity of lunar dust and implications for astronauts. Chronic exposure to dust on earth can cause serious problems, especially to the lungs, but I was surprised to hears some of the other effects. My lack of biology knowledge is probably getting this partly wrong, but Cooper said that very small dust particles can actually enter the tissue around small blood vessels and prevent them from expanding when the body needs them to do so! Not good!

Crushed quartz is quite nasty stuff on earth and Cooper said that there was reason to believe that moon dust might be even more reactive because of its jagged surface, the many fresh fractures in the grains caused by micro-meteorites, and because of solar wind protons. All of these things result in unbonded ions known as free-radicals, which are very reactive and cause damage to the body. Dust loses its danger somewhat when it is exposed to air and all the free radicals are neutralized, but Cooper said that their experiments show this takes several hours. They are working on doing experiments with actual lunar samples and lunar soil simulant to find the exact effects of dust inhalation, but it sounds like this is a significant problem that human explorers will have to face.

A particle of moon dust. Image credit: David S. McKay, NASA/JSC

Finally, at the end of the day there were a couple of talks about the detection of water on the moon with the Moon Mineralogy Mapper on Chandrayaan. The most interesting one, given by Roger Clark, showed that the initial water detection actually underestimated the depth of the water absorption feature because it didn’t correct for an overall slope in the background of the spectrum. With that correction, the mapped water extends to all latitudes. There is still a stronger signature near the poles, but that is superimposed on much more complex variation with geology. There are craters that appear to be digging up material with a stronger water band, but other fresh craters dig up less water-rich debris. He also said that he was cautiously optimistic that they had detected some hematite, an iron oxide responsible for Mars’ rusty color, but said that scattered light in the instrument made it difficult to tell for sure. Clark concluded, saying that he didn’t think that the variation of the band strength observed during the lunar day represented a change in the actual amount of water, but rather was due to the viewing geometry.

The press-released M3 map of water on the moon (blue). With recent corrections (not shown here), the mapped water extends all the way down to the equator.

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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.

A Detailed Look at Water on the Moon

September 27, 2009

It looks like Emily Lakdawalla at the Planetary Society blog has beat me to the punch! After the big announcement that three separate groups have found evidence of water on the moon, she dove in, read the papers and has a series of posts with all of the details of their findings. Well worth a read!

Part 1: There’s Water on the Moon!

Part 2: The Murkier Part of the Story

Part 3 isn’t posted yet, but will be soon. And if you’re interested in space exploration news, you should probably just follow the Planetary Society blog.

Water on the Moon

September 24, 2009

blue_moon

In case you haven’t heard yet, there is quite the buzz building about three separate results that indicate that there is water on the lunar surface. There isn’t much: moon rocks returned by Apollo are pretty darn dry, but it’s still an exciting result, and it means that future missions might be able to extract water for drinking and rocket fuel. I was especially surprised to hear that the water is not just in the frigid craters at the moon’s poles that never see the light of day. Instead, it is found over large portions of the surface! The other surprise is that one of the data sets used to make this discovery is about 10 years old!

Reach more about it in this AP article or this one at Space.com.

The Painted Desert and Petrified Forest

March 22, 2009
The colorful layers of the painted desert formed in the triassic period when meandering tropical rivers deposted layers of mud and clay. Some of these layers are due to volcanic ash choking up the rivers and altering to clay.

The colorful layers of the painted desert formed in the triassic period when meandering tropical rivers deposted layers of mud and clay. Some of these layers are due to volcanic ash choking up the rivers and altering to clay.

(This is the final day of a week-long field trip in Arizona. Get caught up with days 1,2,3,4,5, 6)

Friday was the last day of the field trip, and we spent it at the Petrified Forest national park. We were there to study the colorful clays and river deposits, but we began the day with an unexpected bonus: our guide, Bill Parker, is a paleontologist at the park, and he took us to see some of the skeletons that have been found there, and the people who work on them. I spent much of my childhood wanting to be a paleontologist, so to actually see it in action was a special treat. We learned that there is recent evidence that almost all dinosaurs had feathers! We also got to see the reconstruction of what one of the animals may have looked like based on the skull, which was something that I didn’t realize that paleontologists did.

A paleontologist at Petrified Forest national park chips away at the protective plaster around the skull of an alligator-like dinosaur.

Matt Brown, a fossil preparer at Petrified Forest national park chips away at the protective plaster around the skull of an alligator-like dinosaur.

A reconstruction of what one of the dinosaurs may have looked like, based on its skull.

A reconstruction of what one of the dinosaurs being studied at the park may have looked like, based on its skull.

After the paleontology lab, we continued on to the painted desert badlands, which were the real reason we came to the park. These beautiful formations were formed when Arizona was a flat, tropical floodplain. Many of the layers are actually the deposits from broad, meandering rivers. When they overflow their banks, they deposit sediment in broad layers. In other cases, ash from volcanic eruptions blanketed the landscape, and was altered by the water of the lakes and rivers and rain to become clay minerals like bentonite. The clays expand when they get wet and contract when they dry, and are quite soft to begin with, so that it is very difficult for plants to get a foot-hold. This leads to broad expanses of “badlands” terrain: heavily eroded buttes and mounds of the brightly colored clays and sandstones.

The badlands terrain of the painted desert. The clays in the rocks expand when wet and contract when dry, creating an unstable surface where plants can't get a foothold. The bright colors are from different types of clay, different types of deposits, and different degrees of oxidation.

The badlands terrain of the painted desert. The clays in the rocks expand when wet and contract when dry, creating an unstable surface where plants can't get a foothold. The bright colors are from different types of clay, different types of deposits, and different degrees of oxidation.

We spent a long time studying an outcrop that used to be part of an ancient meandering river or delta. The layers deposited on the shore of a river tend to be angled in toward the riverbed, so by looking at the orientation of thelayers, you can guess at what the river might have looked like.

img_1537_smallClay-bearing river or delta deposits. These may have been deposited extremely rapidly, since there was the fossil of an 8-foot-tall horsetail in the outcrop, still standing upright and crossing several layers!

Clay-bearing river or delta deposits. These may have been deposited extremely rapidly, since there was the fossil of an 8-foot-tall horsetail in the outcrop, still standing upright and crossing several layers!

We were especially interested in this outcrop because we found fossils of giant horsetail plants in them, and the fossils were upright, as if they had been covered in sediment while still alive. That would mean that something like 8 feet of rock was deposited extremely rapidly, before the horsetail died and fell over! We speculated that this could happen during a particularly heavy monsoon season. In the layers with the horsetail there were also some very large rocks that were rounded as if they had been transported by the river.

One of our paleontologist guides, pointing at the two giant horsetail fossils. (click for full-resolution to see the fossils more clearly)

Jeff Martz, one of our paleontologist guides, pointing at the two giant horsetail fossils. Click for full-resolution to see the fossils more clearly.

A close-up of one of the horsetail fossils. The green part is a couple of inches across.

A close-up of one of the horsetail fossils. The green part is a couple of inches across.

After puzzling over the river deposits and trying to reconstruct their story, we ended the visit to the park by taking a look at the petrified forest. Our guide, Bill Parker, told us that all of the petrified trees in the park are missing their bark and branches, and that they likely were part of log jams in ancient Triassic rivers. He pointed out that it is almost impossible to find a modern river that hasn’t been modified by humans, and that in their natural state, these meandering rivers would have been clogged with dead trees. When the trees were buried by sand and ash, the silica in the rocks was dissolved in the water and precipitated out in the cells of the wood, gradually replacing organic matter with silica. The silica logs are much more resistant to erosion than the sandstone in which they are embedded, so as the rock erodes away, the logs are left sitting on the surface.

Petrified logs, formed when silica replaced the organic material of the wood, are more resistant to erosion than the sandstone in which they formed, and end up lying on the surface.

Petrified logs, formed when silica replaced the organic material of the wood, are more resistant to erosion than the sandstone in which they formed, and end up lying on the surface.

You may be wondering what all of this has to do with Mars. Well, the paleontology has very little to do, but the processes involved are quite relevant. Mars likely had liquid water in its past, and certainly had ash and sand deposits. Places like Mawrth Vallis have clay-bearing rocks eroded into channels and buttes and mounds, very similar to the clay-bearing rocks of the painted desert. The same conditions that prevailed to preserve the petrified forest and the dinosaur and plant fossils may also preserve more basic biomarkers, capturing evidence for a habitable Mars.

That concludes our geologic tour of Arizona! I went the first version of this trip two years ago, and then as now I was humbled by how complex and difficult to interpret our planet is, even when we can reach out and touch the rocks and analyze them at our leisure. On the other hand, there were many things that we saw from the ground that were much easier to interpret from aerial and satellite data. When you’re on the ground, it is much harder to get an feeling for the overall shape of what you are looking at. A combination of both orbital and ground-based studies is very important to really begin to understand the geology in detail, and even then there is a lot that we can’t figure out!

This trip has also impressed upon me how much more geology I need to learn. I need to know sedimentology and stratigraphy if I’m going to be attempting to read the story hidden in the layered pages of rock on Mars. But for now, I at least know what it is that I don’t know, and that’s a good start.

Potential MSL Site: Nili Fossae Trough

September 16, 2008

This morning we hit the ground running and heard about a very interesting site: the Nili Fossae Trough. This site would land in a big canyon formed when a block of crust dropped down. To the southeast of the site is the giant Isidis impact basin, and to the south is the Syrtis Major volcano and associated lava flows. Just east of the trough is a somewhat fresher crater whose ejecta fills the area of the landing site, and mand of the crater and canyon walls have sapping channels or river channels in them that give evidence of some periods of wetness for a large portion of Mars’ history.

The mineralogy of the region is spectacular. Within a few hundred kilometers of the site there are volcanic minerals like olivene and pyroxene, many types of clay, and possibly even evidence of carbonates! (carbonates have been a sort of holy grail in Mars science because they could be where all of the carbon in the early thick atmosphere ended up, but nobody has ever seen them in any significant amount from orbit) Carbonates dissolve in acidic waters, so their presence indicates a neutral to high pH in the region, which is generally more friendly to life. MSL would be able to access huge blocks of rock blasted out of the nearby impacts, and also drive to interesting bedrock nearby.

It was argued that Nili Fossae is a good site for habitability because it has a lot of different possible locations and is not dependent upon the microbes being photosynthetic. The potential environments include hydrothermal fractures, sedimentary units, and other subsurface niches. Underground habitats are nice because they are sheilded from radiation and are more likely to be wet due to groundwater.

The nominal mission would begin by landing on ejecta from the nearby crater, and then would drive across lavas from Syrtis Major, onto clay-bearing stuff filling the canyon, and then over to the eroding canyon walls which have a very strong clay signature.

The site is absolutely spectacular in terms of the geology and mineralogy, and if we landed we would get the added bonus of awesome scenery. Unfortunately, it has a tough time making the habitability and preservation case. In the discussion after all of the Nili Fossae talks, many people were critical of the idea that a) the area had hydrothermal activity and b) that MSL could detect evidence of organics in such environments. The argument about this point got very heated, but I think was valuable. One thing that was pointed out that I hadn’t thought about before was that, in a planet with no photosynthesis but lakes on the surface, you would still have life in the lakes because there would be chemical gradients. On earth the only reason that non-photosynthetic life is not up near the surface is because the more efficient photosynthesizers can out-compete it.

There were also concerns about just how long water was present at the site. The presenters kept saying “sustained” wetness, but when pressed on it, they actually said that there were several episodes and I got the impression that they weren’t really sure how long those periods lasted.

The discussion would have gone on a lot longer, but in the interest of staying on time, we moved on. I think Nili Fossae is a really cool site, with great geology but their habitability case is not as strong. It has the advantage that it looks like the clays are “in place” and have not beed eroded and transported from elsewhere. It would also be a really dramatic site with cliffs and mesas unlike anything we’ve ever seen at other sites.

We’ll see if it lasts through this process. If it does, we could be in for some very scenic views from mars, and some fascinating science to boot.

For more thoughts about the Nili Fossae site and the hard questions that were asked, check out Emily’s post over at the Planetary Society blog!

New insights into ancient water on Mars

July 17, 2008

The evidence for a warmer, wetter ancient Mars just keeps piling up! In 2 new papers, the team for the CRISM spectrometer onboard NASA’s Mars Reconnaissance Orbiter has reported new evidence for water on the surface of ancient Mars, based on the ubiquitous presence of water-bearing minerals.

Universe Today has a great post up on the findings, so I won’t repeat too much of Nancy’s explanation.

In brief, the CRISM team has identified a whole new suite of minerals on Mars, in addition to a few already observed, that only form with copious amounts of water. While some of these minerals are associated with local deposits that look like sedimentary layers set down by surface water, others seem to be present across vast regions of the ancient southern highlands. In particular, the minerals tend to be associated with the ejecta, floors, and central peaks of craters in the ancient terrains. Because the impacts probably dug up the minerals from several kilometers down in the crust, the crust must have been altered by water to at least that depth. For example, the image below shows where CRISM has detected phyllosilicates (a hydrated clay mineral) in one region of the highlands. Because almost every crater has a phyllosilicate detection, the basement material has probably interacted with water throughout this region.


Mustard et al. (2008), Figure 4a

We tend to think of “Mars” as one place with a history that can be described by one storyline, even though Mars is a whole planet with as much surface area as dry land on Earth. What’s really great about these findings is that they really bring home that the surface of Mars probably had just as many different environments as Earth does now. Mars scientists have used the composition of minerals and their geologic context to identify ancient hydrothermal springs, shallow seas, lakes, and floods on Mars. With all of these different environments, life very well may have been able to eke out an existence in one of them…