Fourth MSL Landing Site Workshop: Day 1 notes: Introduction, biosignatures, and mineralogy
Posted by Emily Lakdawalla
28-09-2010 17:57 CDT
I apologize in advance for the expanse of text below, but I hope that some of you will find the details interesting. If I took the time to edit these down and plug in lots of pretty pictures from presentations, they'd never get posted! They are my notes from yesterday, the first day of the fourth Mars Science Laboratory Landing Site Community Workshop (see here for the significance of "community"). I'm a reasonably fast typist and tried to write down some of the better comments verbatim, but wasn't recording; any errors in transcription or paraphrase are mine and I'll gladly correct them if I have missed someone's meaning! My editorial comments are enclosed in brackets.  Here is the official program (Word Document format).
arrived late and missed John Grant and Michael Meyer's introductions.
Mike Watkins was up next, giving a status report on the rover's development. The first thing I noted from his talk was that he -- unlike pretty much everyone else who spoke after him -- did, occasionally, refer to the rover as "Curiosity" rather than as "MSL." Clearly the scientists will mostly be using "MSL" to name the rover, both because that's what it's been called throughout its development and probably also because they don't love the name "Curiosity." I'll use "MSL" when they do...
Watkins said "Over the past year, MSL has finally started looking like a rover." We are finishing hardware deliveries, conducting environmental test campaigns, preparing for launch and mission operations, and "completing the V&V program" [what does that mean??] He showed the family portrait of Sojourner, a Mars Exploration Rover, and Curiosity, and commented that "Sojourner can almost run inside Curiosity's wheel like a hamster." Then he showed a pic of Curiosity with her mast raised and arm extended as far upward as it would reach and said that the mast is about the height of a professional basketball player ("like looking Shaq in the eyes, which means that the arm can almost dunk.")
Watkins continued, explaining why no further site possibilities were being considered ("Syrtis was interesting but looked like strain for EDL.") [EDL=Entry, Descent, and Landing, otherwise known as the "six minutes of terror" on a Martian lander mission.] We now know how the landing ellipse is going to be oriented on surface of Mars, because we have finalized Mars approach and entry geometry. The project took advantage of the two-year mission delay to do some design improvements. Among other things, they got a much larger battery: 90% increase in battery capacity. Also, they improved understanding of thermal situation, modeling of actuator heating, and now the rover's performance is "nearly flat across latitude," meaning that it doesn't matter what latitude the rover lands; at a more extreme latitude, the better power situation in summer almost perfectly offsets the worse power situation in winter. "This is one reason we're not talking as much about engineering in this meeting as we might be." [This is crucial; in past meetings, latitude of landing sites was considered a real problem -- it's wonderful news that it's not really a constraint anymore.]
Watkins: "As of today, our 4 final sites are viable for EDL purposes. Not only are they all viable, but from several perspectives, including safety, as of today they are nearly indistinguishable. We don't see a way to give significant distinguishing characteristics between these four sites" from an engineering standpoint. "This is an 80 or 90% science thing." [Again, this is crucial. Science can come to the forefront for Curiosity's landing site selection; there won't be nearly as much pressure as there was with Spirit and Opportunity to select a "safe" site over a scientifically interesting one.] He also commented that we have nearly complete HiRISE coverage of all of the landing sites -- in stereo!
he final landing site recommendation will go to NASA Headquarters next summer.
Next was John Grotzinger, project scientist. His talk was more of a pep talk than anything else, encouraging the gathered scientists not to spend their energy shooting down each other's work, but rather to make the best of whichever site gets picked. "We have too much fear of the unknown. We don't yet know what our resources are. I want everyone to focus on the positive aspects of the landing site. Let's focus again on the science, because that's how we as a project benefit most. We have to pick one of these landing sites. It might not be your favorite site that gets chosen. You're going to have to give away your 18-year-old daughter and say goodbye. We promise to treat her well. These data sets from [Mars Reconnaissance Orbiter] -- HiRISE, CRISM -- they're enormous It's impossible not to get started and change your mind a hundred times about what the bread crumbs are on your way to the pot of gold."
Grotzinger (called "Grotz" by his peers, apparently) gave credit to CRISM team for helping the Curiosity team get image products that help in decision-making. Likewise to the HiRISE team. He said they are now using the color strips in HiRISE images -- the central 10% of each image swath -- to cross-correlate with CRISM, allowing them to map mineralogical detail at a resolution CRISM can't do. He cautioned against an attitude of "we're never going to go there, we're never going to do that. The engineers may pull a trick out of their hats and we won't be able to take advantage because we dismissed it too early. I think all these sites are spectacular." He summarized the four sites thus: "Mawrth is probably the oldest stratigraphic section on the planet, possibly even in the solar system. Gale could be the thickest section exposed in outcrop, unfaulted, not just on Mars but possibly in the solar system. Eberswalde is the best delta on Mars, let's figure out what we can do with this delta. Holden is an alluvial system, with a lake attached to it. At some point, you cross a threshold and say, 'what can I get out of this?' I think it's much easier to take a negative viewpoint and take a swipe at another site than [it is to be constructive and positive]"
Dawn Sumner gave an update on the MSL project's internal review of science sites, Asking what are the top questions that can be addressed in each area, and evaluating how rover resources affect the ability to address these questions. A couple of questioners wondered why the project was even asking those questions, when the science goals of Curiosity had been identified so long ago? She answered that the goals were not articulated in a way that could be used in the tactical, day-to-day operations of the rover.
Habitability and Biosignatures
t the start of each MSL landing site meeting there have always been presentations by people who understand how to search for signs of ancient life on Earth, in the hopes that that will guide how the MSL science team selects a landing site and searches for signs of ancient life or its environments on Mars.
First up was Roger Summons, who gave a report on behalf of the "Biosignature Taphonomy Working Group." ["Taphonomy" was the first of several words I had to look up today.] This working group is charged with developing criteria to identify the environments on Mars that would preserve biosignatures, if they existed. First, he said, look at Earth. "Earth's early record is incredibly cryptic, difficult to evaluate and interpret, riddled with enigmas and controversies." Much of the doubt has to do with tectonism and weathering. Absence of tectonism on Mars is a big help. Orbital cameras provide detailed perspectives. [He didn't say so, but this is truer for Mars than for Earth -- no vegetation to cover up the geology, no active water cycle to destroy it, though of course dust is a problem.]
On the early Earth, oldest records of life on earth take the form of isotopic signatures, stromatolites, and microfossils. Context is everything; the more we know about the context, the more we are able to evaluate the signatures with confidence. Good news is that Mars and Earth environments should be comparable. [He showed several charts summarizing their findings but didn't leave them on the screen long enough for me to copy them down. Here's most of one of the charts. Hopefully the rest will be posted to the landing site selection website eventually.]
|Type of biosignature||Definitive evidence|
or past life?
|Detectable by MSL?|
|Biogenic organic molecules||Highly definitive||readily detectable with SAM|
|Biogenic gases||Highly definitive||Readily detectable with SAM|
|Body fossils||Often definitive||With MAHLI, if they are large enough|
|Biofabrics||Sometimes definitive||With MAHLI, Mastcam|
|Stable isotopic compositions||Occasionaly definitive;|
|Readily with SAM.|
|Biomineralization/alteration||...and he flipped to the next slide. There was one more that I missed.|
Summons continued: an important question is where is organic matter produced on Earth? 90% of all organic matter preserved in geologic record was deposited within 100 km of coastline. [He credited R. Keil of the University of Washington for this statement.] He showed more detailed unreadable tables, but in bold text he highlighted the three environments that have the highest probabilities for both formation and preservation of biosignatures: hydrothermal environments with water temperatures of less than 100°C. Of sedimentary environments the two best places to look are deltas and perennial lacustrine environments. [That is, lakes that are long-lived and stable with the Martian climate, rather than just being an ephemeral pond of water caused by a one-time flood event.] His punch line: early Earth is the best analogue we have for guiding the search for biosignatures on Mars
Jen Eigenbrode looked specifically at how impact cratering will influence MSL's search for past life. She said the three words "Formation, Concentration, and Preservation (FCP) should drive everything we search for, both habitability and biosignatures." How does this play out in impact generated rocks? Consider a pre-impact suite of rocks, which may or may not contain an ancient record of habitat, biosignatures, or organic matter. After an impact, there could be an impact-generated hydrothermal system or an impact-generated crater lake, which is usually a closed system. Both have high FCP potential. But impact-related fluvial environments, sediments, or pedogenesis [soil formation] would not support FCP. If biosignatures in an impact site predate the impact, they can be affected by impact erosion, subsequent oxidation and weathering; shock metamorphism; hydrothermal alteration; redistribution; or overprinting by later life. Devon Island field studies have been helpful for establishing how these processes affect the fossil record. We need to apply yhe MSL payload to identify ecosystems, rather than focusing on biosignatures out of context in their record of life. That's how we overcome ambiguity in looking for extraterrestrial life.
She showed a thought-provoking slide titled "MSL Investigation Pace," comparing field geology on Earth with MSL. For both, the first two steps are similar. On both Earth and Mars, one can begin with aerial/orbital photography to survey the site. On Earth, that would be followed by a foot survey; on Mars, it's the rover's remote survey using its cameras and ChemCam instruments, drawing on the Mars Exploration Rover experience. On Earth, the next steps would be to characterize the rocks by doing in situ sampling, reutrning samples to the lab, lab sample preparation, and analysis. On Earth, all these steps can be run concurrently, but they all consume mission time on MSL. These will all be extremely exciting, but they will be slow. Do we want to spend our time putting together the big picture? We want it all in place as best as we can before we start roving around surface.
The take-home message, Eigenbrode said, is that complex histories, as scientifically intriguing as they are, are likely to increase the difficulty of addressing the mission goal. Having a geological framework before landing allows for better strategic planning. If we don't understand the geologic framework, it will suck up mission time. Having a good idea of what geological framework might be will support efficiency and mitigate risk in mission operations. Specifically considering the four sites: Mawrth: has a complex history and unclear environments. Holden: complex framework, unclear environmental history. Eberswalde has a delta/lacustrine stratigraphic framework [that is better understood]. Gale has a stratigraphic framework, but an unclear environment. "A year ago, I thought, with some of these [landing sites], we're never going to be successful" because they were too complex to understand. "But with everything we have learned, I have completely changed my perspective on this. It's amazing how much we've learned, and we're not done yet."
After she was done, Ray Arvidson stood up and punctured her argument thusly: "A geologic framework is good, but be prepared to throw the framework out completely."
Next up was Dorothy Oehler, who explained how best to find organic biosignatures. "Of the potential biosignatures, the least ambiguous would be accumulations of organic matter. On Earth, these are organic-rich shales and mudstones. They are widespread in geological column, in many geologic settings. They are common even when delicate morphological fossils are not preserved. Shales and mudstones present environments or facies in which organic matter has been both concentrated and preserved. This is what we ought to be looking for on Mars. Rocks like these are source rocks for oil and gas deposits on Earth.
"Basins house Earth's source rocks." She showed an example of oil-bearing half-graben in Libya. "This is a well-known oil province, based on thousands of wells and full geochemical profiles. The [oil] source rocks are in the grabens. Shales taper up onto platforms; they are thinner and organic content is low. So we are looking for containers for organic matter. We are also looking for distal facies, because they concentrate fines.
"What variables affect preservation of organic materials on Earth? "Concentration. We want hydrated sites to concentrate material. We want to look for fine-grained sediments, because this minimizes exposure to oxidizing fluids (clays are good). And burial is good. Sediments at surface do not preserve organic material for billions of years. Sediments that are buried and compacted do. Burial compacts sediment and reduces porosity even more. Compacted shales are very effective seals for gas.
She summed her talk up this way: With Curiosity "We are trying to find oil and gas where no man has gone before."
Lindsay Tierney gave a well received talk, in which she explained she was trying out a different mantra than "follow the water": "What I'm interested in is geochemical energy." We can quantify geochemical energy, figure out which ones have more available energy and more potential biomass. We are looking at chemolithoautotrophic organisms. She showed how she calculated how much geochemical energy was available in the past to potential life forms on Mars in different environments. She demonstrated that lacustrine settings might not have enough geochemical energy to support chemosynthesis. Hydrothermal alteration and interesting redox chemistry sites will have more biological potential. Of the four sites, Gale and Mawrth may have had more biological potential if we are just considering the possibility of chemolithoautotrophy.
fter lunch, we were treated to some updates from the CRISM team. CRISM is an imaging spectrometer on Mars Reconnaissance Orbiter. Spectroscopic data is hard for non-spectroscopists to understand. The CRISM team has been working really hard not only to improve the quality of their data through better calibration but also to provide data products that non-spectroscopists can understand.
Frank Seelos was up first. He said they're on the cusp of a major reprocessing of the entire CRISM data set. They put MSL landing site area data at front of the reprocessing queue. They will be supplying MSL data before the next planned PDS release. He showed the issues with the data that they are now working on calibrating out. CRISM data can have two residual effects: an along-track shading due to gimbal motion of instrument, and an across-track bluing of the edges due primarily to atmospheric effects. Both of these are being fixed empirically. All of the browse products are now being re-derived from spectral data that has been corrected. He showed a blink comparison of images before and after this latest recalibration, demonstrating amazing improvement in data quality and removal of high-frequency noise. The data is available here.
Selby Cull gave a progress report on a new effort from the CRISM team. CRISM has already been demonstrated to be great at finding hydrated and hydroxylated minerals, but now we can show you we can estimate relative abundances and grain sizes of minerals. We just got the data about a month ago; these are very preliminary results." That's all the notes I took from her talk -- it was a progress report and very exciting but no conclusions yet.
Next up was Ray Arvidson, giving an update on Opportunity rover science, providing experience from an existing rover mission. I didn't hear anything I hadn't heard before for Opportunity science. He talked quite a bit about the smectite at Endeavour's rim, mentioning that Steve Squyres wants to get Opportunity to "get phyllosilicates identified before you guys even land." He turned to Paolo Belluta, a rover driver who was sitting in the front row, and playfully asked, "When are we going to get there?" Paolo answered, "A couple of years." Ray said "No way, that's too long."
The big news in Ray's talk had to do with CRISM. He showed that they are now trying out a new mode on the instrument. CRISM gets its data by gimbaling as the orbiter passes over a site. They are now trying the same trick that Mars Global Surveyor's Mars Orbiting Camera team did to increase their resolution, gimbaling faster to compensate for the orbiter's motion, a trick that the MOC team called "PROTO." Regular CRISM images have square pixels about 18 meters on a side. New PROTO CRISM images have rectangular pixels 18 meters wide in the cross-track dimension but only 6 meters tall in the along-track dimension. Ray showed a smectite map of Endeavour's rim at this new level of detail. Awesome.
A questioner asked Ray to offer some advice for landing site selection from the Mars Exploration Rover mission. He said, getting to Gusev was driven by geomorphology. [Mars Global Surveyor] TES said it was dust, but Dave DesMarais called what we actually found a "basalt prison." By serendipity we were able to get to Columbia Hills, and our very first measurement was goethite [a mineral that requires water to form]. Since then, the whole complexion of the mission has changed to joy. You can't see any of these minerals from orbit because the outcrop scale is too small. For Opportunity, we knew that the surface had crystalline hematite basalt, in the great discovery from TES. Plus it was a safe site. I thought it was volcaniclastic. Nobody could have predicted that the hematitic signature comes out in the blueberries. Serendipity comes into play; for both sites, Mars has been fantastically richer than we thought it would be."
That's all the notes I took yesterday. After that, they started going into site-specific presentations, where different groups of scientists talked to advocate for why each specific landing site would be the best for Curiosity's science goals and capabilities. This part of the meeting is likely to get contentious, because many of these scientists have invested years in researching each site, and most feel that to not send Curiosity to their chosen site would be to throw away their years of work. Ryan Anderson gave his presentation on Gale crater yesterday and thus was reasonably stress-free (I hope) to take notes from today's presentations on Mawrth, Holden, and Eberswalde. I'll link to his blog entries when he writes them! I will be returning to the meeting tomorrow, which will return to more general discussion of the four sites' merits.
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