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Planetary News: Cassini-Huygens (2007)Reports from the 2007 Lunar and Planetary Science ConferenceSpecial Coverage from The Planetary Society WeblogMarch 12-16, 2006Scientists Bethany Ehlmann, Jason Perry, Anne Verbiscer, Brad Thomson, and Tom Swulius sent these reports from the 38th Lunar and Planetary Science Conference to Emily Lakdawalla for posting in The Planetary Society Weblog, covering some of the latest news from Saturn and Mars. LPSC, Monday: Mars Reconnaissance Orbiter press conferenceMar. 12, 2007 | 19:49 PDT | Mar. 13 02:49 UTC
I was sent this update on today's press conferences at the Lunar and Planetary Science Conference by Bethany Ehlmann, currently a graduate student working with Jack Mustard at Brown University. Thank you Bethany!! --ESL by Bethany Ehlmann Today's press conference on the Mars Reconaissance Orbiter mission highlighted recent findings from the HiRISE and CRISM instruments. As a member of the CRISM team myself, I often attend these press conferences--I'm always curious about how our science comes across to others and what kinds of questions get asked. We look at the data every day so it's great to see it from someone else's perspective. Relating a few site-specific results to the big picture of Mars history is the most exciting part. Shannon Pelkey, a postdoc at Brown University, led off the panel reporting discoveries of ancient phyllosilicate materials at two sites on Mars. Our group at Brown (I'm a graduate student there) has focused in on studying two sites around different parts of the huge Isidis impact basin, the long fractures of Nili Fossae and the ancient highlands of Terra Tyrrhena. Both of these sites contact phyllosilicates, which are a type of silicate mineral (for example clays) and form through contact of rock with liquid water. A key question is how long ago these minerals formed?
The clay question has been one that requires a lot of teamwork among different missions to answer. Phyllosilicates were first discovered on Mars by Jean-Pierre Bibring and the French group in charge of ESA's Mars Express OMEGA instrument in 2005. Everywhere they found clays the terrain was old (as dated by crater counts), leading to the hypothesis that clays were restricted only to ancient terrains and their formation was restricted to early Mars history when the planet was warmer and wetter. This was a hypothesis that needed to be tested, though. OMEGA views the surface of Mars at a resolution of around 300 meters per pixel. This is really good for a spectrometer, but still pretty coarse; small-scale geology couldn't be tied to the mineral composition. Were the phyllosilicates some sort of lake or ocean sediment? Or were they part of an alteration front -- either from the seepage of precipitated water from above or groundwater below? If they had formed from seepage of water from below, it'd be difficult to say when alteration had occurred. Just because the surface of the terrain was old, it didn't mean the alteration had to be old too. This is where CRISM and Shannon's two sites in Nili Fossae and Terra Tyrrhena come in. Both provide unique windows into the layering of the Mars crust. CRISM targeted these two spots based on phyllosilicate detections from OMEGA, a great example of teamwork between missions and collaboration across continents. CRISM collects images at higher resolution, around 20 meters per pixel, allowing us to get a finer-scale view of the composition by looking at the reflection of light in 544 different colors. HiRISE can target the same spots as CRISM. While HiRISE doesn't directly provide mineral detections, it captures images of the morphology at resolutions below 1 meter! At Nili Fossae, several tens of meters of erosion has taken place, exposing three layers of rock strata for examination by the MRO instruments. CRISM found materials with three distinct compositional signatures: phyllosilicate on the bottom, then a layer a couple of pixels wide of olivine, all topped by a "bland" unit of mesas which didn't have an obvious mineralogic signature. Looking at the side of an outcrop of rock with both CRISM and HiRISE, the phyllosilicate layer (the mineral indicating interaction with liquid water) is in sharp contact with olivine (a mineral in igneous rocks which weathers rapidly in the presence of water). This seems to indicate the phyllosilicates were present when the olivine was deposited on top rather than being weathered from below as part of groundwater interaction. Had groundwater from below been responsible for alteration, it's doubtful there would have been a sharply defined olivine layer. We know that the olivine is ancient because of what geologists refer to as cross-cutting of features. The Isidis basin is old, dated around 3.8 billion years and it created fractures (the Nili Fossae) that cut through the phyllosilicate unit. So the phyllosilicates must have been there before the basin. Cratering as an aid in dating also plays a role at the second site discussed: Terra Tyrrhena. To understand how requires a little knowledge of what happens when an impact occurs. The impacting meteorite actually crashes far deeper into the surface than the depth of the crater as seen today. Some material is vaporized and a shock wave from the impact results in the fracturing of rock in and around the crater. The fractured materials are driven downward by gravity, flowing into the surface of the crater. Exactly what happens next is a matter for some debate among cratering experts, but some of the deeper material is for certain pushed upward during the confluence of material in the center of the crater. So a 30-kilometer crater like the one Shannon showed can pull material from as deep as 3 kilometers beneath the surface! Interestingly, the material observed by CRISM contains phyllosilicates, indicating that phyllosilicates are deeply buried under terrain already known to be ancient. Both of these sites support the hypothesis made after OMEGA discovered phyllosilicates: they were formed during an early wet period. Then Mars climate changed, becoming drier so we no longer see them in the younger geologic record. This was just one science story at the press conference, of course. Dr. Yves Langevin (of the IAS, University of Paris) and Dr. Tim Titus (USGS) presented CRISM results from the south polar cap. Bright regions are those with abundant carbon dioxide frost, and dark regions are dusty. It's an unstable environment, though, and change is expected. We're moving into the southern summer and temperatures at Mars' south pole are warming. This means carbon dioxide frost doesn't stick around on the surface but instead begins to sublime into gas. Over the course of three days, CRISM observed growth in dust spots, probably blown out of the subsurface in mini-jets of material as trapped carbon dioxide gas escaped, blowing dust out with it. Quite a dynamic place during the change of the seasons and I wouldn't want a future Mars astronaut to be walking near these things when they blew! The press conference finished with some stunning 3-d image wizardry from the HiRISE team's Randy Kirk (USGS). HiRISE adds a new amazing technical capability to our Mars observing capabilities: stereo imagery at 20-centimeter resolution! HiRISE does this by taking two images of the same spot from slightly different angles. Using a little bit of trigonometry and some powerful computing software, the stereo image pairs can be used to back out the third dimension: topography! One of the first uses the stereo images have been put to is helping in planning of the operation of the Mars Exploration Rovers. I worked on this mission for nine months and got used to the view of the Columbia Hills and Meridiani Planum from one meter off the ground, the top of the rovers' camera masts. The HiRISE stereo provides a whole new perspective! The 3-d images give scientists a hang-glider's view of the terrain. Getting the bird's eye view is a huge asset in seeing the geology and planning the rover's day to day drives. Detailed knowledge of the slopes also helps the MER planning team to align the rover so its solar panels are tilted for maximum sun, getting a few more watt-hours out of the solar array and allowing more science to be done. [NOTE: I'm told that these perspective views will be released publicly sometime soon. --ESL] The press conference only gave a brief sample of the activities of MRO. But it's exciting to see how we use CRISM and HiRISE to follow up on the OMEGA discoveries of the past few years as well as work with the MER teams to plan the science of the future. We're continually looking for new discoveries of our own of course, and there have been a few. Some will be talked about tomorrow at the LPSC sessions. Otherwise, stay tuned until the next press conference. LPSC: Wow, Titan can be a Really Flat Place, and other Titan TalksMar. 12, 2007 | 21:09 PDT | Mar. 13 04:09 UTC
I was sent this update on the Titan sessions at LPSC by Jason Perry, a member of the Cassini Imaging Team and an undergraduate student at the University of Arizona. He used to write a blog called Titan Today, and is a big fan of Io. Thanks Jason!! --ESL  by
Jason Perry
This week's Lunar and Planetary Sciences Conference (LPSC) in Houston, Texas, is the fourth time I have been to this conference. The previous three trips to LPSC were to present a poster, either about the Gish Bar Patera volcano on Io or Cassini ISS images of Titan. This year, however, I presented a talk, during Monday's Titan session. The session was filled with the latest results from Cassini's many instruments, including RADAR, ISS, and the Visible and Infrared Mapping Spectrometer (VIMS). The first two talks in this afternoon's session covered results from the Imaging Science Subsystem camera onboard Cassini. The first talk, by Elizabeth Turtle, gave a general overview of recent results from ISS. Perhaps the biggest news is a large lake, a sea even, discovered in Titan's north polar region late last month.
The northern portion of this sea, extending over 1,100 kilometers across with an area nearly equal to that of Earth's Caspian Sea, was also seen by RADAR during the late February T25 encounter, a couple of days prior to the ISS observations. [Here's that lake. --ESL] However, to date, ISS has yet to see a specular reflection (similar to what you see when seeing lakes late in the afternoon from an airplane) that would definitively indicate the presence of liquids. The identification of this dark feature as a lake, therefore, is based on the morphology of the feature and the appearance of the sea in RADAR. I gave the second talk of the session, covering ISS observations from a flyby in late October 2006 (T20). This high-resolution observation covered a portion of Titan's trailing hemisphere. This region contains the bright streaks the VIMS team interprets as mountain chains based on data taken during the same encounter. The region also contains several features that share many of the morphologic characteristics seen in lake-like features seen in the polar regions by ISS and RADAR. These features are seen in an area where clouds have repeatedly been observed by ground-based observations and VIMS. Again, we haven't observed specular reflections at these sites, so we can't say for sure if these features are lakes, but they are certainly worth a closer look by RADAR.
The next few talks were given by members of the RADAR science team. Besides the usual talks about lakes and dunes (don't worry, I'll talk about those in a minute), perhaps the most interesting talk was one given by Ralph Lorenz on the RADAR altimeter. Precious little data has come out of the RADAR team regarding the altimetry experiment, save some early plots from our first Titan encounter. Much of the older data was subject to significant errors due to uncertainties in the position of Titan early on in the mission, but these uncertainties have been significantly reduced, and better-quality results have been obtained. Lorenz presented a number of plots of altimetry data, showing the utter flatness of the dune fields, though individual pulses do sense both the top of the dunes and bottom of the dunes, and these two altitudes agree with earlier topographic measurements from the RADAR SAR data. Lorenz also presented altimetry data over a portion of the ISS T20 mosaic, which might provide a chance at co-analysis. This greater confidence in the usefulness of the altimetry mode on RADAR has led to the development of a several-thousand-kilometer-long altimetry swath to be acquired during an encounter in May 2007. This swath will also be used to test the reliability of "altimetry from SAR", a technique of using the RADAR SAR's central beam as an altimeter, potentially increasing the amount of altimetry coverage on Titan. Jani Radebaugh and Karl Mitchell of the RADAR team also presented talks, on the dunes and lakes seen by RADAR, respectively. Each new RADAR swath in recent months has provided additional observations of the lakes observed in the north polar region and the dunes observed within the equatorial dark regions. These results support many of the original conclusions, that the dunes represent an pole-to-equator transport of dark Titan sand (made possibly of benzene, so I suggest one not eat Titan sand…), with the occasional diversion around a local topographic high, and that the dark north polar features really are lakes filled with liquid, though some partly drained lake basins have also been observed. One interesting result from Karl Mitchell's talk suggests that the amount of liquid covering Titan's surface fits nicely with a prediction made by a research group led by Giuseppe Mitri, finally published last month in the journal Icarus. The overall climate pattern suggested by RADAR, of relatively humid polar regions supporting lakes on the surface and relatively arid equatorial regions leading to great sand dune seas, is supported by Mitri's model. Two other talks rounding out the afternoon session covered VIMS results at Titan. The first talk, given by VIMS Principal Investigator Bob Brown, covered evidence for a large impact basin in the eastern part of the dark region known as Aztlan. The eastern portion of this dark region is bounded by a semi-circular bright region, interpreted by Brown and his group as the eastern portion of this large impact basin. Based on VIMS' spectral data, the interior of the possible impact basin is filled with the longitudinal dunes that are ubiquitous within Titan's equatorial dark regions. Jason Barnes gave another VIMS' Titan talk, this time on co-analysis of VIMS and RADAR data of dark spots and channels in eastern Xanadu. His analysis shows that some of the dark spots seen by VIMS and ISS are in fact, when seen by RADAR, small mountain ranges. Further analysis suggests that water ice-enriched material eroded from these mountains is channeled away and deposited along the margins of Titan's bright terrain. Luckily, my laptop's battery power just barely made to the end of the last talk of the Titan session, allowing me to type notes for all the talks at the session. The next four days will be a little strange for me, since I usually have to wait longer to present my work, this year I am finished by the end of day on Monday. There will no doubt be many interesting presentations to attend before Friday. LPSC: NASA Night: Improvements to research and analysis fundingMar. 13, 2007 | 14:23 PDT | 21:23 UTC
Brad Thomson just sent me this update about NASA Night at the Lunar and Planetary Science Conference, which took place yesterday evening. At NASA Night, representatives from NASA Headquarters speak to the gathered scientists about current and future funding, priorities, and policies of NASA, and how they may be changing. Brad is a postdoc at the Jet Propulsion Laboratory, working on wind abrasion studies for application to Mars' past environment. -- ESL by Brad Thomson
So this new plan is to have the review panels and program officers divide up the proposals into three categories: Selected, Selectable, and Not Selected. Letters (and money) can go out to those in the Selected much quicker, and those in the Not Selected category can move on to other things. As additional money becomes available, it can be used to fund some percentage of the proposals in the Selectable category. As a young scientist, I think this is great idea because the overall process is much smoother -- no longer is everything held up until all of the budget dust-ups settle out. LPSC: Tuesday: Volcanism and tectonism on Saturn's satellitesMar. 14, 2007 | 13:12 PDT | 20:12 UTC
I received this report on the Tuesday afternoon special session on volcanism and tectonism on Saturn's satellites from Anne Verbiscer, an astronomer from the University of Virginia who I first met at the Division of Planetary Sciences meeting in 2005. She recently published an interesting paper in Science about how Enceladus' spewing water ice particles coat the other satellites of Saturn and make them brighter, which I've been meaning to write about. Most of the links below go to the PDF-format abstracts of the scientists' talks. Many thanks to Anne for her notes! Toward the bottom, she notes the discussion of possible geologic activity from Dione! --ESL by Anne Verbiscer
My notes on the next paper by Glein et al. are more sketchy... They report on hydrothermal geochemistry as a source of plume gases on Enceladus. Using the chemical composition from Cassini's INMS instrument, they have constructed thermodynamic models which try to match observations. The presence of oxidized, reduced carbon is intriguing. INMS has found no carbon monoxide and no ammonia, so the models must match this. They investigate various petrologic combinations -- fayalite, magnetite, and quartz (doesn't work); magnetite and hematite (unrealistic); pyrrhotite-pyrite-magnetite (works) -- and model an early Enceladus as having a global ocean under a thin ice shell on top of hot rock. The oxidation of primary minerals (e.g. iron) was driven by the escape of molecular hydrogen (H2). The ocean may have been quenched hydrothermal fluid. Organic matter decomposition might have been a source of organic compounds. Sarah Newman reported a potential discovery of hydrogen peroxide on Enceladus by Cassini from a weak absorption at 3.5 microns where hydrogen peroxide has a combination band. (it also has bands at 6.9 and 7.2 microns, but these are out of VIMS' reach). Hydrogen peroxide has previously been detected on Europa at a concentration of 0.13% and trace signals were also detected on Ganymede and Callisto (but only in the UV). (Unfortunately, when asked, Sarah could not provide an upper limit for the concentration of hydrogen peroxide on Enceladus.) They have found that the position of this H2O2 band shifts depending on location on Enceladus: on the tiger stripes, between them, and globally. The band is stronger and shifted to higher wavelengths in the south polar terrain. The reason can be due to higher concentration there, more amorphous ice, or a temperature effect. Because hydrogen peroxide is a product of the irradiation of water ice particles, a questioner pointed out that their model has problems if particles don't spend enough time in the plume (presumably to be exposed to the radiation that is going to produce the hydrogen peroxide?). Francis Nimmo reported on tidally driven shear heating as the source of heat for the south polar terrain. The required shear velocity is high. Their model requires a rigid shell thickness of five kilometers. Their model predicts three areas in the tiger stripes which should be at the highest temperatures (if their models are correct). Cassini can test this and to some extent has already with those November 2006 high-resolution CIRS observations. Terry Hurford's paper really got good with the predictions of plume activity from tidal models. The idea is that since Enceladus is in resonance with Dione, its eccentricity is maintained at 0.0047. [This is a measure of how out-of-circular its orbit is. Although very close to circular, the non-circularity in combination with its synchronous rotation means that Saturn raises tides on Enceladus that bend and flex its interior, generating heat. --ESL] The height of the tide changes 1% daily and it oscillates in longitude 0.5% daily. (Europa's numbers are larger, of course.) So, based on where Enceladus is in its orbit, he models the stress along the faults in the south polar terrain. First he put the camera observations of the plumes in the context of Enceladus' orbit. In the November 27, 2005 view, Enceladus was near apocenter and all the tiger stripes were in tension. On January 16 they were at the 3/4 orbit position and on February 17 they were at 1/8 orbit before pericenter. He showed many maps of the south polar terrain with areas along the tiger stripes color-coded to correspond with whether or not they were in compression or tension. The highest plume activity seems to be correlated with when the "rift" first opens (beginning of tension). He mapped out how the stress changes through the orbit. The faults open through pericenter passage. There is an image sequence coming up next month (April) in which his predictions will be tested. The tiger stripe known as Damascus will be opening and in view of the cameras. He predicts an extremely active eruption sequence. (We'll see!) The greatest activity is near the apocenter, lowest at pericenter. There was a question about why no plume activity was seen on Europa (since the same stress calculations have been done for it...) A Galileo observation sequence was planned for this, but at the time, all of the faults were in compression. Also, gravity is much higher on Europa, so any plumes won't go nearly as high on Europa as they do on little Enceladus.
Jeff Moore spoke on the topography of endogenic features on the non-Enceladan satellites of Saturn. He's produced digital elevation models (DEMs) from Cassini by combining stereogrammetry with photoclinometry. He found tectonic features on Rhea along longitude 270° west, which form a great circle. Rhea may have bright frost deposits coming out of fractures (this is from an old Dave Stevenson paper). Rhea has graben sets, ancient ridges (Moore had a paper in 1985 on the "mega scarps" on Rhea). Dione is globally smoother than Rhea, with resurfaced plains bound on the west by a ridge, then rises to the east. An old impact feature called Amata has reappeared from the DEMs. (In early Cassini images it was thought to have disappeared; it was a feature originally written up as an ancient impact basin in the Smith et al. Science paper after the Voyager flybys in the early 1980s). Tethys has concentric circles antipodal to Odysseus, possibly a result of seismic focusing from the impact (that produced Odysseus). The smooth plains on Tethys really are smooth, which shows evidence of volcanic resurfacing.
Then things really got interesting with the report of the detection of activity on Dione: Jared Leisner et al. report on Enceladus and Dione as sources of Saturn's neutral cloud from the magnetometer on Cassini. They found that Enceladus is (of course) the dominant source of water group ions, but that Dione is also a source, producing 6.5 grams per second, which is an order of magnitude above what would be produced from sputtering (0.4 grams per second). There is no evidence that Tethys is a mass source, in fact, if anything, it looks like it's a mass sink. My battery ran out here, so, switching to handwritten notes: Bob Nelson reported the detection of cryovolcanic activity on Titan! From Cassini VIMS observations, they examined a bright spot on the surface (after checking carefully that they were not just observing a cloud that changed in size/brightness, etc.) which has changed between July 2004 and March 2006. It has increased in brightness and has changed spectrally (changed its brightness at specific wavelengths). By comparing models of various materials, methane ice, water ice, etc. the only close (not perfect) match came from modeling ammonia frost on top of water ice. (I asked him after the talk if they've looked at ammonia hydrates and they plan to do so but have not yet.) Paul Schenk asked if it could be ground fog. LPSC: Tuesday: A walk through the morning Mars Reconnaissance Orbiter abstractsMar. 14, 2007 | 14:56 PDT | 21:56 UTC
Apart from Anne Verbiscer's contribution on the Saturn satellite geology talks, I haven't received anything else regarding yesterday's sessions at the Lunar and Planetary Science Conference. There was a big to-do in the press yesterday about the discovery of that huge north polar "sea" on Titan, a topic that I'll have more to say about later, when I can be more thorough. In the meantime, I'll direct you to a news story by Amir Alexander, "Cassini Reveals "Seas" of Methane and Ethane on Titan," and point out that I have updated the Titan RADAR images page with all the latest-released images, including the entire swath captured during the February 22 ("T25") flyby. In an effort to present you some of the information from Mars Reconnaissance Orbiter, I read through the abstracts from yesterday morning's special session. Fortunately, LPSC abstracts are some of the longest of conference abstracts; they're more like mini-papers and can run as long as 1,500 words. The abstracts for this conference were due on January 9 of this year, so they represent the state of things about two months ago. All the links in the discussion below go to PDF copies of abstracts. The style of special sessions on newly-arrived spacecraft is that each instrument team gives an overview of their instrument's capabilities, and as quickly as possible shows stunning new images from their instruments; the abstracts rarely feature these images, as the teams typically prefer to show the "latest and greatest" that their instruments have produced. But two of the teams -- HiRISE and CRISM -- have been releasing quite a few pictures to the Web, so I can show you some good stuff here. Alfred McEwen presented initial results from HiRISE. There was an interesting table in his abstract showing how the HiRISE targets have been selected by science theme, and what they have managed to capture so far:
Here's a look at one HiRISE image released today, which (I am guessing) may be part of that "dunes database" that contributes to so many "Aeolian Processes"-themed HiRISE images. It is also -- if you'll read on to the CRISM talk -- context for a study of the locations of water-lain sediments on Mars. As is usual with HiRISE images, there are things to be appreciated in the image at every possible scale, so I'll show chunks at resolutions of 10 meters (top), 1 meter (middle), and 25 centimeters (bottom) per pixel.
Following the HiRISE presentation there was one by Mike Malin on the two cameras he's got on Mars Reconnaissance Orbiter -- MARCI and CTX. Here's one cool image that's been released from CTX showing a dozen active dust devils:
And a detail:
Next up was Scott Murchie presenting on CRISM. Like the HiRISE team, their observations are split into science themes; even better, you can search the publicly-released CRISM images by theme on their website. So it was quite easy to find that they have already released an image corresponding to the region of the dunefield HiRISE image I showed you above, and it contains a scientific puzzle.
CRISM is being used as both a mapping instrument -- with the goal of acquiring a medium-resolution (hundred-meter-per-pixel), 72-color map of most of the planet -- and as a high-resolution instrument, where it acquires coverage of small areas at roughly 15 meters per pixel in 544 different colors. Scott's abstract reports some stats of CRISM's mapping so far: as of January 1, they've acquired 192 of the targeted observations, have nearly completed their survey mapping of the high northern latitudes, and have mapped 20% of the planet at lower latitudes. (They had to focus on the high northern latitudes while there was still sunlight at the north pole; after the equinox on February 8, more and more of the polar regions are obscured by winter darkness.) Roberto Seu gave a presentation on SHARAD, the shallow subsurface radar instrument on Mars Reconnaissance Orbiter. SHARAD differs from MARSIS on Mars Express in that it achieves higher resolution at the expense of ground penetration depth -- it can penetrate only the top several hundred meters, where MARSIS sees down several kilometers. The abstract reports that "The first observations were actually slightly affected by a bug in the flight software that caused a limited random error in the observation timing. However, with an additional handmade processing, the science Team has had in any case the possibility to analyse very good data mainly on both poles. A new version of the flight software has been successfully reloaded and tested at the beginning of December 2006 and the bug has been fixed. Since then SHARAD is operating fully with the nominal expected performance." In fact, in some places, SHARAD has achieved a penetration depth of over a kilometer. Maria Zuber reported on the status of the Mars Reconnaissance Orbiter gravity field observations from radio tracking of the spacecraft. Even though the "early mapping mission data is non-optimal for precision analysis because of the proximity of the spacecraft to solar conjunction, which results in a relatively high level of noise due to solar plasma," the results obtained so far look quite spectacular when compared with a gravity map derived from two full years of Mars Global Surveyor radio tracking observations: "It is interesting and significant that even using a single month of MRO tracking data near solar conjunction, we obtain a field with higher signal than the MGS field. Visually, the MGS and MRO fields are not easily distinguishable." You can compare the two maps in a diagram on the second page of her abstract. Matt Golombek reported on the sizes and distributions of boulders in the northern plains of Mars where Mars Reconnaissance Orbiter has been targeting potential Phoenix landing sites. They systematically measured the diameters of rocks by measuring the length of the terminator (bright-dark boundary) in the direction perpendicular to the direction of solar illumination, and measured their heights by measuring the length of the shadow parallel to the direction of solar illumination. They counted all rocks over areas of ten to thirty thousand square meters. When I say "they" here, I'm pretty sure that most of this clicking and measuring was done by the abstract's third author, undergraduate student Tabitha Heet. They found that the rock abundances measured in HiRISE images agreed well with those derived on the ground from Viking 2 images, and suggest that the Phoenix lander should be aimed at places having less than 5 or 10 percent rock abundance as seen in HiRISE images. Kevin Seelos presented on CRISM observations of the Phoenix landing sites. One of the useful things in this abstract is just a listing of the most up-to-date geographical information on the location of the Phoenix landing site: "three candidate landing error ellipses centered at 1) 68.35°N, 233.0°E, 2) 66.75°N, 247.6°E, and 3) 71.2°N, 253.0°E." He also reports the important observation that preliminary analysis of CRISM data acquired over these three sites "reveal the occurrence of water ice on several north-facing slopes of crater rims and other topographically elevated features. The late summer seasonality of these observations (solar longitude 132-160°) and location generally less than 72°N makes these 1-2 km wide patches of ice surprising." He goes on to say that ice hasn't been seen exposed at the surface in the flatter areas where Phoenix will likely land, but that's good news; the perfect Phoenix landing site will have ice located within a meter or so of the surface underneath a nice layer of dirt that they can dig through and analyze. They won't be able to get many more images before the advancing season precludes further coverage.
LPSC, Wednesday: A preview of the Mars Exploration Rover sessionMar. 15, 2007 | 08:27 PDT | 15:27 UTC
I received these notes on Wednesday's Mars Exploration Rover sessions from Tom Swulius, a frequent poster on unmannedspaceflight.com. He's promised more information later but wanted to give a preview of the high points of yesterday's session. Thanks Tom! --ESL by Tom Swulius
The last presentation of the morning session was by Paul Knauth on the impact surge hypothesis. I thoroughly enjoyed the presentation, where he demonstrated with photos just how similar the bedding/lamination characteristics of impact surges can be to those of aeolian and subaqueous bedforms. He also demonstrated that impact surge deposits are fairly common on Mars, and that they can have quite large runout distances. He mentioned that this phenomenon needs to be modeled in more detail, which is probably true. Such deposits are surely going to be an important part of the Martian geologic story, regardless of whether they relate to the sediments at Meridiani. [Knauth and coworkers oppose the Mars Exploration Rover's interpretation that the Meridiani rocks were once wet. --ESL] He also mentioned that such deposits should be expected to be rich in sulfides, the reasons for which I didn't fully understand (perhaps because reduced iron species might be expected in deeply excavated craters?). But he noted that sulfide-rich sediments could be viable targets for future astrobiological studies. As you might expect, his paper seemed to bring out more than the usual number of detractors in the Q&As after his talk. But in the end it seemed clear to me that he was making some valid points. LPSC, Thursday: Icy satellitesMar. 15, 2007 | 17:33 PDT | Mar. 16 00:33 UTC
There was a short session at the Lunar and Planetary Science Conference this afternoon devoted to the icy worlds of the solar system not presently considered cool enough to be seen with Titan or Enceladus. That's only half a joke -- there were three previous complete sessions during the week with talks on those two moons of Saturn, whereas this six-talk half-session contained all but one of the oral presentations there were on any other icy body, including Europa and Pluto! (The talk wasn't even about Pluto -- it was about Charon.) There were, of course, posters to be seen on these other bodies, but I found it really striking that there were only two talks this year on Europa. Anyway, Anne Verbiscer has come through for me with notes on the talks from this session. Thanks, Anne! --ESL by Anne Verbiscer
Amanda Hendrix presented Cassini UVIS observations of Iapetus and Phoebe in the far ultraviolet (FUV), from 110 to 190 nanometers. In the FUV as in visible light, the polar cap of Iapetus is bright and the leading hemisphere is dark. In the FUV, water ice has a characteristic absorption at 165 nanometers; she examined the strength of this feature as a function of latitude. From 0-30 degrees north, the feature is the weakest; it's a little stronger between 30 and 40 degrees; and is strongest between 40 and 50 degrees. Interestingly, when she compares the strength of this feature on Iapetus with that on Phoebe, the bright terrain on Iapetus is a closer match to Phoebe than the dark terrain, leading her to surmise that it is probably not "pure Phoebe" material that contaminates the dark side of Iapetus. In fact, Iapetus' light terrain matches Hyperion better than it does Phoebe. On the other hand, Iapetus' dark terrain doesn't match Hyperion or Phoebe; both Phoebe and Hyperion are too water-rich to match the dark terrain on Iapetus. She presented spectral models in which Hyperion is composed of 55% water ice and 45% Triton "tholin", and Iapetus' dark terrain as 5% water ice and 95% Triton "tholin". Their detection of water ice at the lowest, warmest latitudes of the dark apex region on Iapetus suggests an ongoing or recent implantation/coating process, which is consistent with the lack of fresh craters in the thin layer of dark material. Hyperion may be a better candidate for the source of Iapetus' dark material, primarily because of the color (red) similarities. They cannot rule out an endogenic source of dark material or a water-rich layer under the dark material as a source of the water. There will be a good Iapetus flyby in September which will provide coverage of the trailing (bright) hemisphere. Roland Wagner presented a talk on the global geology of Rhea (from Cassini ISS) which agrees with much of the results already presented at this meeting by Moore and Schenk. Rhea shows no clear evidence for cryovolcanic resurfacing as seen on Dione (see abstracts by Moore, etc.). His digital elevation maps (DEMs) reveal degraded impact structures as well as extensional, compressional, and shear tectonic features. The observed tectonic structures may have been produced by phase changes, from Ice I to Ice II. Rhea has, of course, one ray crater on its leading hemisphere, which is difficult to date because of the order of magnitude difference between crater frequencies in areas surrounding the crater. (Ray craters are not common on Saturnian satellites.) Rhea shows similar tectonic features as those seen on Dione, but its endogenic evolution ceased earlier in its history. Wes Patterson discussed "non-transform structural discontinuities (NSDs)" on Europa, primarily Belus Linea. The terrestrial analogs to NSDs are overlapping spreading centers which are almost exclusively observed in areas of thin oceanic lithosphere. On Europa, we see obvious segmentation at Belus Linea which has a bright interior flanked by dark material on either side. (These are the old Voyager "triple bands" which Galileo showed were not really bands, but instead complex ridges.) The dark material flanking these complex ridges may represent erupted volatiles brought to the surface via water-filled cracks initiated at the base of the ice shell. (This mechanism has previously been proposed (and published) by Crawford and Stevenson.) Kevin Zahnle presented "Io Attacks!" (which I'm really interested in the analogies to the same idea in the Saturnian system that I just published in Science last month with Enceladus' "cosmic graffiti art"... but that's another story)... Basically the idea here is that ejecta from Io are launched into orbit around Jupiter and about 8% of this material actually hits Europa, just about everywhere except the polar regions and on the trailing hemisphere. Impact velocities are 3.5 kilometers per second. His "off the shelf" theory provides a good match to the observed size-number distribution of small craters on Europa. He refers to the resulting craters as "sesquenaries"... neither primary nor secondary... So, Ionian basalts are an important source of vitamins and minerals on Europa! Finally, Steve Desch presented a talk on cryovolcanism on Charon and other KBOs (a subject relevant to my own poster on observations and models of Charon near-infrared spectra incorporating ammonia hydrate). Steve interprets the 1.65 micron band of crystalline water ice as the hallmark of cryovolcanic activity. [I'll note as an aside here that this spectral feature is prominently seen in just about all bright, icy Saturnian satellite spectra, such as those of Rhea, and I just wrote above about how there is no evidence for cryovolcanism on Rhea, so there's a problem here...] Crystalline water ice should amorphize on relatively small timescales because of exposure to cosmic rays, etc. The spectral feature of crystalline water ice is seen on KBOs larger than 500 kilometers in diameter, and not in the spectra of smaller KBOs. He presented thermal evolution models of a differentiated Charon. LPSC, Thursday: Mars postersMar. 16, 2007 | 10:57 PDT | 17:57 UTC
Bethany Ehlmann, currently a graduate student working with Jack Mustard at Brown University, just sent me this update on the Mars-related posters that were presented yesterday at the Lunar and Planetary Science Conference. If you'd like to read the poster abstracts, visit the LPSC 2007 abstract webpage. Thanks Bethany!! --ESL by Bethany Ehlmann One of the best ways of getting a snapshot of the state of Mars science is to peruse the poster sessions at a major conference like the Lunar and Planetary Science Conference or the American Geophysical Union meeting. The spread of posters is a good barometer of what the science community is most excited about. I hadn't been to LPSC for nearly three years, so the advances made over the intervening time really stood out. In some ways, I like poster sessions at LPSC meetings more than the spoken presentations. For those who have never been to a poster session at a scientific conference, it's not too different from your local science fair in structure. Scientists prepare 36- by 48-inch posters providing a snapshot of their research. Then you stand by your poster, talking about your findings to anyone who asks. The sessions are extremely interactive, mingling students and 30-year veterans, space mission instrument developers with instrument users, and asteroid researchers with Mars geologists. There's ample time to discuss and question, using figures on the posters as aids. It's a really a sea of information. Like a surfer you have to pick which waves to ride; the session is only about two hours long and you can't talk to everyone. So you browse for the posters most interesting to your work. Here are the highlights from my perspective: Findings from the Mars Reconnaissance Orbiter, which just started its mapping in October, were hot. The biggest buzz was over the north polar deposits. On Mars, northern hemisphere winter has now set in. High-level ice clouds mean no good observations of the pole until one Mars year from now--summer 2008! A long time to wait. Luckily, before the winter set in, all instruments of MRO waged an intensive campaign to image the poles, collecting enough data to keep scientists busy until the next round of observations. For the first time, the SHARAD radar provided an image of the three-dimensional structure of the pole as radar waves penetrated the layers and were reflected back to the spacecraft. CRISM captured the distribution of water ice deposits in craters near the poles -- which are presumably stable? [If you can find water ice in a crater at the end of summer then it's probably stable over many Mars years. --ESL] CTX, HiRISE, and CRISM together provided a suite of observations of Chasma Boreale, a huge gash into the center of the pole which exposes its layered structure. The poles are a bit of an enigma -- a basal (base) unit which looks a lot like aeolian sands is covered by banded polar layered deposits. These are probably successive layers with differing amounts of dust and ice. Climate affects the nature of deposits on the pole (in terms of the amount of dust vs. water ice vs. carbon dioxide) so the hope is that we can back out information on Mars climate history. Scientists on Earth drill for ice cores in the Arctic and Antarctic to reconstruct climate history. Mars scientists hope the polar layered deposits will provide similar insights, especially now that we can see the layering on scales smaller than one meter. Stay tuned to upcoming issues of Science magazine with the new results.
Mars mineralogy has come a long way in the past decade. With data in the thermal infrared wavelengths from TES [on Mars Global Surveyor] and THEMIS [on 2001 Mars Odyssey] and data in the visible and near infrared from OMEGA [on Mars Express] and CRISM [on Mars Reconnaissance Orbiter], we have a detailed mapping of the planet's mineralogy. Folks are now eager to pool findings. You see, TES and THEMIS are fabulous at detecting silica-bearing rock and oxides. These are minerals that you can find in the dark volcanic rock called basalt, for example olivine, pyroxene, and feldspar. Iron oxides include hematite, which we find at Terra Meridiani, Opportunity's landing site. TES even allows us to estimate percent abundances of each mineral. You can't do this (yet) with CRISM and OMEGA. But what those two detect well are sulfates and phyllosilicates, minerals that we know formed in the presence of liquid water. [Sulfates include minerals such as gypsum (typically deposited during sea water evaporation) and jarosite (typically formed as a result of iron sulfide weathering); phyllosilicates include mica and clays, which typically form through the weathering of rocks and the alteration of their minerals in the presence of water. --ESL] By combining these data sets, there's great potential to nail down the mineralogy more firmly. Did the phylloslicates form from altering olivine? Are the sulfates mixed with basalt? Which minerals are on top and which are on the bottom of the stratigraphic sequence? Or in other words, which came first? Folks who stare at spectra and hyperspectral images (the reflected and emitted light at different wavelengths) were talking eagerly to each other in the hope of merging information from the two wavelength regions.
Lastly, the findings of extensive aqueous alteration at Terra Meridiani by the Mars Exploration Rovers have spurred geochemists to weigh in with models and lab experiments, trying to replicate conditions that might lead to the formation of sulfates and hematite spherules. How would conditions at sulfate-rich Terra Meridiani been different from those at the phyllosilicate-rich Nili Fossae which we see from orbit? The amount of water relative to rock, the acidity, types of dissolved ions, and atmospheric composition all dictate which minerals form. There were numerous posters on evaporation of salt assemblages. Two interesting models of a more global nature were presented to help explain the observation that phyllosilicate minerals occur earlier than sulfate minerals in Mars history. David Fernández-Remolar presented the idea that groundwater flushing of sulfides in the subsurface may have caused the precipiation of sulfates, sometime after surface weathering had formed clays. This situation is similar to acid mine drainage on Earth at a site in Spain called Rio Tinto where we get extensive Terra Meridiani-type salts. Itamar Halevy described the influence of early outgassing of sulfur dioxide in creating conditions favorable for an early, mild greenhouse effect and precipitation of clays and sulfites. ["Sulfite" is the SO32- ion, which is less oxidized than the "sulfate" ion, SO42-. --ESL] When the outgassing ceased and sulfur dioxide abundance decreased, the Martian environment became highly oxidizing, perhaps causing the sulfites to transform to sulfates. Can OMEGA, CRISM, THEMIS, and TES look back at the data to try to identify sulfides or sulfites? It's something we'll pay special attention to. It's an exciting time in Mars science, with new missions spawning new ideas and pulling together new groups of scientists. Just as we've pieced together the geologic history of ancient Earth, we're starting to unravel the mysteries of early Mars. LPSC, Tuesday: More from Mars Reconnaissance OrbiterMar. 17, 2007 | 09:42 PDT | 16:42 UTC
I got this update on the last few talks from Tuesday morning's Mars Reconnaissance Orbiter special session late yesterday from Brad Thomson. His notes gave me an excuse to download and show you some of the tremendous HiRISE images from Holden crater on Mars. Thanks Brad! --ESL by Brad Thomson
The last two speakers were Jack Mustard from Brown University and Jean-Pierre Bibring from IAS University in France. Jack presented further analysis of the Nili Fossae region of Mars where previously the OMEGA instrument on the European Mars Express spacecraft has detected the presence of phyllosilicate (clay)-rich material. Layers rich in the mineral olivine overlie the clay-rich layers. Since clays indicate water alteration of rock while olivine indicates little to no water, the inference here was that early on there was water available, and then conditions changed such that water was no longer available.
Jean-Pierre prefaced his talk on coupled OMEGA-CRISM observations by noting that 20 years ago both Jack Mustard and Scott Murchie, the principal investigator of the CRISM instrument, participated as young scientists in the Thermoscan instrument on the Russian Phobos 2 spacecraft. So the collaboration between the European and American spectroscopists has deep roots. As usual, Jean-Pierre quickly flashed from slide to slide in his information-packed talk. One interesting point I took home from his talk is that iron and magnesium clays appear to be spatially distinct from alumina-rich clays. [See Bethany's discussion of this topic in the previous blog post. --ESL] These two types of clays represent different degrees of weathering (generally aluminum-rich clays indicate a greater amount of weathering) and/or differences in the starting rock composition. Both Jack and Jean-Pierre stressed that with the combined knowledge from the currently operating orbital spectrometers and the ultra-high resolution HiRISE images, one can begin to understand not just what minerals occur but also the stratigraphic order and environment in which they formed. LPSC, Wednesday: Two talks from the Mars Exploration Rover sessionMar. 19, 2007 | 13:38 PDT | 20:38 UTC
Tom Swulius sent me these notes on the first two Mars Exploration Rover talks of Wednesday's session. As he's a geologist, his notes are pretty detailed on the field geology being conducted by Opportunity in Meridani Planum. Thanks Tom! --ESL by Tom Swulius
OPPORTUNITY RESULTS AT VICTORIA CRATER, MERIDIANI PLANUM. S. W. Squyres and the Athena Science Team. Steve Squyres began by showing a route map overlain on a HiRise image of the region of Meridiani Planum where Opportunity landed and has been roving for 1100+ sols (almost 3.25 years). He quickly summarized the trip south from Eagle/Endurance Craters to Victoria Crater, which Opportunity is currently exploring. He pointed out that along the southward trek the team noticed the that number and size of the concretions (blueberries) embedded in the sulfate-rich sandstone bedrock were decreasing. Opportunity had climbed in elevation and probably had climbed to higher levels in the geologic section as it roved southward, and the thought is that it had climbed to a level that was above the paleo water table that controlled where the concretions could grow in the bedrock. When Opportunity came to the outer edge of Victoria's annulus, the team noticed a great abundance of loose concretions lying on the surface. It is thought that the edge of the annulus represents the outer edge of the ejecta blanket of rubble thrown out of Victoria Crater during the impact. Their hypothesis is that concretion bearing rubble, excavated from deeper layers of bedrock in the crater, became part of the ejecta blanket. Much of the friable sandstone blocks eroded relatively quickly, releasing the more resistant blueberries onto the surface. Thus, the edge of the concretion rich annulus defines the extent of the original ejecta blanket. If the team can find a safe route into Victoria, it is thought that the layers bearing the concretions might be observed. This is the level that Steve has previously described as the bathtub ring. On a different theory related to the spherical concretions Steve said that they are thinking that places where loose blueberries are abundant on the surface might control the distribution of the large, wind-blown ripples. Near Eagle and Endurance the loose concretions were abundant and the ripples were few and very small. As the rover drove south the berries became less common and the ripples became numerous and sometimes very large. Then, when Opportunity arrived at the edge of the berry-rich annulus, the ripples magically disappeared right at that edge. Steve said that it is possible that abundant concretions on the surface creates a surface roughness that inhibits the saltation of sand grains, and thus the growth and migration of ripples. Concentrating on Victoria Crater itself, Steve brought up a route map of Opportunity's exploration of the rim of that crater up until sol 1111. He mentioned that in the walls of the crater they can see three general layers: The ejecta layer on top, a zone of very fractured, but otherwise in-place bedrock below the ejecta, and then mostly solid bedrock below that. Their cameras and mini-TES have not so far observed any major change in bedrock lithology in the crater walls. It may be that the same sulfate-rich sandstone extends beyond the base of the visible cliffs. The hope has always been that within the more deeply excavated Victoria Crater some new, deeper layers might be discovered. The team is still looking, though. One reason they have been so interested in the dark cobbles that are distributed across the surface around some parts of the crater rim is the hope that some of them may be fragments of a still deeper layer that became part of the ejecta mix. If such a layer contributed ejecta fragments that were more resistant to erosion than the sandstone, they could be left stranded randomly on the surface as the softer ejecta blocks erode. Ones such cobble that Opportunity recently investigated was the target named Santa Catarina. Steve said Santa Catarina's composition was | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
NASA
Night was a most interesting evening. Jim Green, the new Director of the
Planetary Science Division, spoke at length about what I consider to be
a vastly improved way to implement funding for research and analysis grants
(known as R&A funding in NASA parlance). Under the previous system,
there was often a significant delay (nine or more months in some cases)
between when grants were due and when the announcements about which ones
actually got funded went out. There were several reasons for the delay
that basically revolved around the instability of funding to and within
NASA. For example, Congress has been passing continuing resolutions rather
than budgets, which freezes spending at the previous fiscal year's level.
There are many other budgetary factors besides, but the end result is that
too often these selections get held up until the funding situation is fully
settled. Understandably, this leads to considerable anxiety among us in
the science community who are left waiting in limbo for months without
end.
In
a report on 
Steve
Squyres mostly recapped recent mission activities that serious rover fans
already know, but he did suggest that they are not really seeing, nor expecting,
any outcrops significantly different from the sulfate-cemented sandstone
we have seen so far. Regarding rumors we've heard that Opportunity will
enter Victoria through the Valley Without Peril, he was carefully ambiguous.
He first mentioned that they understand that the rovers are not immortal,
and they are committed to enter Victoria somewhere if they can go in and
come out safely. He went on to say that "hopefully" we would
see them enter soon. Adding a bit of cautious humor, he noted that the
Valley Without Peril is named for a place on Magellan's voyage that is
not far from where Magellan was killed. He also seemed fairly excited about
the beautiful aeolian cross-bedding we are seeing in Cape St. Vincent.
