Posted tagged ‘mars’

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.

Spirit Rover Discovers Carbonates

June 4, 2010

Big news from Mars today, Spirit has found evidence for significant amounts of carbonates in the rocks of Gusev crater! Carbonates are really important for two reasons: first of all, Mars has a very thin CO2 atmosphere right now. Too thin for water to remain as a liquid on the surface: it would just boil away and freeze at the same time! But there is lots of evidence that water once flowed on the surface. That means it must have been warmer and the atmospheric pressure must have been higher.¬† A good way to get higher pressure and temperature on the planet would be to have more CO2 in the atmosphere (just take a look at Venus!). But then the question becomes “where did it go”? On Earth a lot of our CO2 is trapped in carbonate rocks like limestone, so the thought was that maybe carbonates could store some of the CO2 on Mars. But until now they have been very hard to find. The Phoenix lander found evidence for a little bit, and orbiting spectrometers have identified some tiny patches that look like carbonates, but this finding by Spirit is much more conclusive.

Carbonates are also important because they dissolve quite easily in acid. The fact that there are rocks on the surface at Gusev Crater that have carbonate minerals in them means that they have not been exposed to much acid, and therefore the environment was much less hostile to life.

I’m going to paste the full press release here, but I also want to note how cool it is that my adviser at NASA, Dick Morris, is the lead author of this study! He does extremely careful and detailed work, so if he is confident enough to publish this finding, I have no doubt that it is true. Congrats to everyone involved on this awesome discovery!

NASA Rovers Finds Clue to Mars’ Past and Environment for Life

The "Comanche" outcrop may be up to one-quarter carbonates. Image Credit: NASA/JPL-Caltech/Cornell University

PASADENA, Calif. — Rocks examined by NASA’s Spirit Mars Rover hold evidence of a wet, non-acidic ancient environment that may have been favorable for life. Confirming this mineral clue took four years of analysis by several scientists.

An outcrop that Spirit examined in late 2005 revealed high concentrations of carbonate, which originates in wet, near-neutral conditions, but dissolves in acid. The ancient water indicated by this find was not acidic.

NASA’s rovers have found other evidence of formerly wet Martian environments. However, the data for those environments indicate conditions that may have been acidic. In other cases, the conditions were definitely acidic, and therefore less favorable as habitats for life.

Laboratory tests helped confirm the carbonate identification. The findings were published online Thursday, June 3 by the journal Science.

“This is one of the most significant findings by the rovers,” said Steve Squyres of Cornell University in Ithaca, N.Y. Squyres is principal investigator for the Mars twin rovers, Spirit and Opportunity, and a co-author of the new report. “A substantial carbonate deposit in a Mars outcrop tells us that conditions that could have been quite favorable for life were present at one time in that place.”

Spirit inspected rock outcrops, including one scientists called Comanche, along the rover’s route from the top of Husband Hill to the vicinity of the Home Plate plateau that Spirit has studied since 2006. Magnesium iron carbonate makes up about one-fourth of the measured volume in Comanche. That is a tenfold higher concentration than any previously identified for carbonate in a Martian rock.

“We used detective work combining results from three spectrometers to lock this down,” said Dick Morris, lead author of the report and a member of a rover science team at NASA’s Johnson Space Center in Houston.”The instruments gave us multiple, interlocking ways of confirming the magnesium iron carbonate, with a good handle on how much there is.”

Massive carbonate deposits on Mars have been sought for years without much success. Numerous channels apparently carved by flows of liquid water on ancient Mars suggest the planet was formerly warmer, thanks to greenhouse warming from a thicker atmosphere than exists now. The ancient, dense Martian atmosphere was probably rich in carbon dioxide, because that gas makes up nearly all the modern, very thin atmosphere.

It is important to determine where most of the carbon dioxide went. Some theorize it departed to space. Others hypothesize that it left the atmosphere by the mixing of carbon dioxide with water under conditions that led to forming carbonate minerals. That possibility, plus finding small amounts of carbonate in meteorites that originated from Mars, led to expectations in the 1990s that carbonate would be abundant on Mars. However, mineral-mapping spectrometers on orbiters since then have found evidence of localized carbonate deposits in only one area, plus small amounts distributed globally in Martian dust.

Morris suspected iron-bearing carbonate at Comanche years ago from inspection of the rock with Spirit’s M√∂ssbauer Spectrometer, which provides information about iron-containing minerals. Confirming evidence from other instruments emerged slowly. The instrument with the best capability for detecting carbonates, the Miniature Thermal Emission Spectrometer, had its mirror contaminated with dust earlier in 2005, during a wind event that also cleaned Spirit’s solar panels.

“It was like looking through dirty glasses,” said Steve Ruff of Arizona State University in Tempe, Ariz., another co-author of the report. “We could tell there was something very different about Comanche compared with other outcrops we had seen, but we couldn’t tell what it was until we developed a correction method to account for the dust on the mirror.”

Spirit’s Alpha Particle X-ray Spectrometer instrument detected a high concentration of light elements, a group including carbon and oxygen, that helped quantify the carbonate content.

The rovers landed on Mars in January 2004 for missions originally planned to last three months. Spirit has been out of communication since March 22 and is in a low-power hibernation status during Martian winter. Opportunity is making steady progress toward a large crater, Endeavour, which is about 11 kilometers (7 miles) away.

MarsSed 2010 Field Trip Day 2: Stromatolites, Gypsum and Layers

April 29, 2010

We started off Day 2 of the field trip by driving up onto the eroded rocks of what used to be the tidal flats of the ancient reef, between the shore and the continental shelf. The closest modern-day analog to the rocks that we visited is the Persian Gulf, where you have an arid climate and deposition on the shelf and down into the deeper ocean basin. In the tidal flats and lagoons of the ancient sea where the rocks that we visited formed, the water was only a few meters deep, and was a nice place for blue-green algae to grow. You might think that a bunch of single-celled organisms wouldn’t leave much of a mark in the geologic record, but you would be wrong!

The wavy layers in the carbonate rocks here are stromatolites - fossil backterial mats that grew in the shallow tidal flats and lagoon behind the ancient reef.

In fact, cyanobacteria growing in tidal flats tend to form thick, wavy mats that are then preserved and fossilized, forming “stromatolites”. Stromatolites are among the oldest evidence of life on the Earth. We spent quite a while discussing the stromatolites here, and particularly learning how to tell the difference between wavy layers that are biogenic and those that are due to things like sand ripples or deformed layers that were originally flat. The variation of the layer thickness is the first hint: stromatolites tend to be thicker in low points and thinner in high points. If the waviness was due to the deformation of originally flat layers, there shouldn’t be a change in thickness between highs and lows. Another hint is if you can tell that the waviness forms domes rather than parallel ridges, and especially if you find isolated domes or columns. It’s difficult to form an isolated dome-shaped ripple, but that’s exactly what you get when mounds of cyanobacteria are growing.

Modern stromatolites growing in Shark Bay, Australia. Original image by Paul Harrison.

After looking closely at stromatolites, we drove closer to what was the ancient shore and encountered an abrupt transition to layered gypsum and silt beds deposited as the near-shore pools periodically dried out. This area was used as the “slow-motion” field test for Mars Science Laboratory in 2007. The science teams essentially practiced by sending someone out here to take pictures and samples, and the team tried to understand the site without any other information. For our field stop, we took a look at some infrared maps of the minerals in the area, and then climbed a nice exposure of them.

We climbed "Tepee Hill", a nice exposure of gypsum and mudstone layers deposited in the evaporative shelf lagoon.

In the afternoon, we drove to “Last Chance Canyon” to admire an excellent exposure of the inclined beds that characterize the transition from the continental shelf to the ocean basin. The curves of the canyon let us see the tilted layers from different angles to get a good three-dimensional feel for the stratigraphy. We spent a while sitting up on one side of the canyon and sketching the opposite side and then hearing from our expert guides about all the subtle details that we amateurs had missed in our sketches.

The upper layers here are flat-lying, but below them, the layers begin to dip down to the right. These dipping beds were deposited on the slope of the shelf margin. Don't be fooled by the diagonal dark green vegetated stripes that go from upper right to lower left - those are fractures in the rocks where plants have taken hold.

It started to rain while we were studing the outcrop, but lucky for one member of our group, he was carrying the large canvas print-out of the Burns formation, a well studied section of rocks on Mars. Turns out it makes a decent cloak.

Our penultimate stop of the day was not listed in the guidebook but was pretty interesting. We took a look at some of the carbonate layers that had curious features called “tepee structures”. The leading theory for how these structures form is that, when carbonate deposits dry out, new minerals form and cause the layers to expand, causing them to buckle upward. There’s still a lot of debate about how they formed, however. They’re interesting to us martians because in an overhead view, the buckled zones form polygons, and there are polygonal features all over on mars.

A good example of a "tepee structure" is visible in the rocks here, just right of center. Geologists aren't completely sure how they form but the leading theory is that it has something to do with the rocks expanding as they dry out and new crystals form.

Our final stop was also not listed in the guidebook. We decided that since we had been talking about the ancient reef so much that we should take a look at it. Within the carbonates of the reef we found a lots of interesting fossils, including a texture that looked like miniature stromatolites, large spiral shells, and crinoid remains.

That concludes Day 2 of the field trip! Day 3 was a visit to Carlsbad Caverns – stay tuned for lots of pretty pictures!


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