Summary of Pasadena MER 2003 Landing Site Workshop October 18-19, 2001

See Program for Titles and Presenters of Individual Talks in Each of the Following Sessions

Edited by J. Grant and M. Golombek

The morning introductory session summarized the status of the Athena instrument payload, status of the current ellipse size of landing sites and engineering constraints, update of the MER program, discussion of the application of the MOLA pulse spread widths, and a presentation on the hematite landing sites within Sinus Meridiani.

The session started with a welcome and introduction of landing site committee Co-Chairs John Grant and Matt Golombek who then gave a brief overview. The meeting had originally been postponed from September and the venue moved from Cornell University to Pasadena California. This was the second meeting for selecting landing sites specifically for the MER 2003 mission. Two other landing site selection workshops were held in 1998 and 1999 for the original 2001 and subsequent lander missions for the Mars Surveyor program. These meetings have been scheduled as a mechanism for garnering and soliciting feedback from the planetary community on landing site selection issues.

Steve Squyres gave an update on the Athena payload flight system and mission design. The payload development and testing are proceeding well. The flight system and mission design have problems but Steve feels that the flight team is excellent. He said that the instrument and payload people are present at the meeting and can answer any questions.

Jim Garvin gave an update of the Mars Exploration Program and discussed implications of MOLA pulse spread data for landing site selection. He stated that the Mars program is ongoing with Odyssey on track and funds for two extended missions included in the five year budget. He said that despite the rumors, there are still two MER rovers and that the Mars Reconnaissance Orbiter ’05 selection is still on track for November 8, 2001. Beyond the near term set of missions, the rest of the program is based on projections, but still includes the Mars Scouts in 2007, with Netlander contribution. The smart lander is very challenging due to power constraints and the science still needs to be worked out. The integrated sample return mission is delayed until at least 2011. The very earliest concept stage may include SAR in 2009 with ASI.

Garvin then discussed the MOLA pulse width data in deriving MOLA slope and vertical roughness over the 140 meter MOLA footprint. Roughness in the MOLA footprint is determined by pulse dilation through interaction with terrain. Slopes are derived by determining the vertical roughness of pulse dilation with correction for tilt. For Mars there is a 1.1 modal pulse width distribution; this is a narrow range compared to Earth and suggests that the surface of Mars is generally smooth, like Earth’s deserts. A low pulse width means low tilt and low residual roughness. Pulse widths ranging between 0-1 imply that the surface is very smooth and that it is not populated with lots of megablocks down to the 1.5 meter scale; 1-2 is pretty smooth; 2-3 is getting rough and 9-3 is very rough. Bimodal pulse width distributions can imply the presence of two different units or a rough unit such as lava flows. There was concern over the Gusev landing site, as it is the only candidate landing site with a bimodal distribution thus implying a mixed unit. Gusev has both a high pulse width and a high surface roughness suggesting blocks or corrugations at the subscale of MOC image resolution. However he cautioned against using these data sets alone to exclude a landing site.

John Grant gave an update on the landing site selection process, including the membership of Additional members from other Mars missions have been added to the steering committee to add continuity to the selection process. He reviewed the site selection process schedule over the past year. The goal of this workshop is to reduce the potential sites to four with a couple of backups.

Mark Adler summarized the current engineering constraints. The landing ellipse is defined by three parameters, its semi-major and semi-minor axes and its azimuth. The ellipse size has decreased for some sites and increased for others. He mentioned that even if they decreased the EDL (Entry, Descent, Landing) margins for navigation, that the ellipse would still not fit in some landing sites. For example, the ellipse would shrink from 211 km to 119km for MER-B for the hematite site and from 141 km to 108 km for Gale crater. There was also concern over the rock abundance at the various landing sites. Phil Christensen cautioned to not consider the rock abundance numbers in an absolute sense. He suggested that it would be better to compare the rock abundance in a relative sense and to compare ranges of numbers, such as 0-5% rocks, 5-15% rocks and greater than 15% rocks. There was also concern over egress at the various candidate landing sites, so that the lander’s ramp can open and allow the rover to roll onto the Martian surface. If the rock abundance is too high, then the ramp may not be able to openprovide an egress route. There was concern about the high rock abundance of the Isidis basin sites, although Christensen commented that the rock abundance at Isidis was probably ok.

Matt Golombek and Tim Parker gave an overview of the current landing ellipse sizes. The ellipses have gotten larger to the south and in doing so have eliminated grown too large to fit within some of the crater sites such as Boedikker and Gale Craters, as well as some canyon sites.

Phil Christensen gave the first landing site talk of the workshop on the Hematite sites located within Sinus Meridiani. He outlined his the reasons for going to these sites as well as presented possible origins. He emphasized the uniqueness of the hematite unit, claiming that it’s 10 micrometer or larger grain sizes imply crystalline material and that crystalline hematite supports a unique chemical process that very likely involved water. He summarized what he thought were the possible origins: lacustrine, hydrothermal, igneous and indurated volcanic airfall and that his favorite was hydrothermal although there were pros and cons for each mechanism. He underscored the usefulness of the Athena payload for this site as the instrument payload can confirm if the unit is indeed hematite. In addition, by analyzing the deposit’s physical characteristics such as grain size, rounding, sorting and bedding, they should be able to determine if, for example, it is an indurated volcanic airfall deposit composed of glass and ash or whether it is composed of basaltic grains. Discussion afterwards focused on the low albedo and rock abundance of the site and how it will likely look very different from the three landing sites we have been to and the lack of dust to inhibit remote sensing identification of geologic materials by the rover.

Phil Christensen reported on TES mineralogy results and the MER hematite sites in Sinus Meridiani. TES data planet-wide show large expanses covered by dust and by basaltic to andesitic mineralogic signatures. No evidence for carbonates, clays, or chemical weathering (unaltered olivine has been detected) occurs.

Hematite at >5% abundance occurs locally and correlates with stratigraphic units in Sinus Meridiani (SM), Aram Chaos, and central Valles Marineris. The age of the SM deposit, which caps a layered sequence, is debatable; Bill Hartmann believes that circular structures in the deposit seen in MOC images represent exhumed craters within the unit; however, others suggest that the craters may be in underlying material. While the deposit may be exhumed, no extant overlying material has been detected.

The SM ellipses have medium to low thermal inertia and low rock abundance. Albedo is low (0.080.12), suggesting that little dust occursis on the surface. The SM signatures record as much as 10-15% hematite in TES spectra.

Leading interpretations for the hematite include chemical precipitation in iron-rich surface or hydrothermal water, thermal oxidation of lavas, or indurated volcanic airfall. Pros and cons exist for each. MER will be able to evaluate these possibilities by measuring mineralogy (particularly iron-rich minerals), grain-size distribution, rock textures, rock coatings, and various structures that may be diagnostic of lacustrine, igneous, and hydrothermal processes.

Tim Parker reviewed the Melas Chasma (MC) and Central Valles Marineris (CVM) sites. The CVM site, in Coprates Chasma, does not include layered deposits, nor does the ellipse fit safely between the chasma walls.

The MC site fits within lower sloping terrain at MOLA resolution. MOC images show that the ellipse includes patches of interior deposits, dunes, sand sheets, low buttes, and landslide material. Only a little interior layered deposits occur in the ellipse. The more prevalent interior deposit does not show layering but forms a collection of round pancake-like features with raised rims. Parker suggests that these features may result from subaqueous landslides, perhaps derived from interior layered deposits present higher up on the chasma walls. Outside of the ellipse, a MOC image shows dense channels that drain into a higher, perched basin level, which Parker thinks may related to drainage of a former lake ~ 3 km deep. Bright banding on the chasma wall, instead of buried lacustrine layers as suggested by Malin and Edgett, could be lake deposits plastered against the chasma walls; Parker showed how such bright layers coincide with former levels of Pleistocene Lake Bonneville in Utah. Further MOC images are needed to provide more complete mapping of features and units in the MC ellipse.

Steve Squyres interjected that MER TCM6 maneuvers are being prepared (but the decision to perform them has not been made) for execution six hours prior to the landings. If these are indeed undertaken, they may permit moderately improved positioning within the ellipses.

Larry Crumpler discussed the two Isidis MER sites, and proposed five more positioned closer to the Libya Montes highlands. In contrast, the Beagle ellipse is much larger and farther north in bland plains material, which would permit comparative analyses of plains materials proximal and distal to the highlands. The highland rocks forming massifs of the Isidis impact basin include ancient highland rocks dissected by valley networks. The valleys apparently fed deposition into a series of perched basins and intermingle with various highland deposits and Syrtis Major lava flows, indicating a complex, multi-stage, and long-lived fluvial history. Broad valley floors are up to 100 km wide, and narrow valleys within them in MOC images show complex floor morphology. Tectonic deformation also seems to have affected drainage history. Highland craters may have formed local thermal sources that could have driven long-lived hydrothermal systems.

High TES thermal inertia signatures on the southern margin of Isidis Planitia occur where larger valley systems enter the lowlands, at about —3500 m elevation. These areas may constitute rocky fan deposits formed in a relatively low-energy fluvial environment. They also have high fine-component thermal inertia, which may be explained by a duricrust soil. Phobos ISM data indicate ferrous iron associated with the Syrtis Major lava flows and more ferric rocks generally making up Libya Montes and Isidis Planitia. In the ellipses, rock abundance varies from 12-24%.

The Athena instrumentation could sample the mineralogic and lithologic diversity of expected Fe-rich highland, sedimentary, and volcanic rocks, as well as their weathering rinds, in the fans below Libya Montes,. Crumpler has produced a 350 MB, zoomable Canvas image of the Isidis landing-site region containing the Viking MDIM, MER ellipses, geologic features, and MOC images.

Nathalie Cabrol, Crater lakes I: Gusev, Boedikker, and "Unnamed" EP69A

Gusev:

Gusev is a 158-km-diameter impact crater, with an estimated 10,000 km³ of impact melt in the vicinity. It has been supplied with water episodically from Ma’Adim Vallis, which flows into the crater. With the combination of large amounts of heat and the availability of liquid water, there is the possibility of occurrence of hydrothermal systems, and hydrothermal or aqueous alteration of surface minerals. In addition, there are features indicating both fluvial and ice-related processes.

Deposits in the interior of Gusev Crater are interpreted as having been deposited from the water flowing in from Ma’Adim Vallis, with features including depositional deltas, for example. The deposits suggest that there were at least three episodes of activity:

(i) The youngest deposits appear to be sublacustrine or subaerial, and there may not have been a standing lake in Gusev at that time. (It is likely that sublacustrine and subaerial deposits can be distinguished from the ground, at least based on terrestrial examples.) These deposits fill about 20 % of the current landing ellipse.

(ii) Intermediate-age deposits are interpreted as indicating a fluvio-lacustrine episode. These fill about 40 % of the ellipse. As seen from the ground, sediments in this area might include varves, for example, or layers representing longer periods.

(iii) The oldest material was deposited directly from the Ma’Adim flows, and may have overtopped the 20-km-diameter impact crater Thyra in places. This indicates that Thyra predated the first episode, and that residual heat may even have been present to drive hydrothermal activity. These deposits occupy about 32 % of the ellipse. The contact between the oldest and intermediate surfaces is interpreted as indicating the presence of an ice-covered lake, and fills about 1 % of the ellipse.

In summary, the merits of Gusev include:

(i) It is one of the few places that has had a prolonged and episodic hydrological history.

(ii) The fluvial and depositional history spans a large portion of Martian history.

(iii) Water and energy are available, and the effects identifiable, so that this is a region that is viable for the support of life.

(iv) Gusev has been used as an example in ongoing efforts in education and public outreach, with a substantial amount of work in the schools, for example, so that its use as a landing site would provide obvious and enhanced connections to the public.

There was some discussion of the MOC images that do not show clear evidence for layered material within Gusev and the relatively dusty nature of the site.

Boedikker:

Boedikker is considered as a backup to Gusev in terms of having evidence for an interior crater lake. However, the evidence that an interior lake existed is relatively indirect, and not enough work has been done to support its selection as a landing site.

EP69A:

Crater EP69A is also considered a backup to Gusev. However, substantial problems for it as a landing site include:

(i) The landing ellipse is too large to fit within crater interior, so there are safety concerns at the margins.

(ii) There is not enough MOC coverage within the site, so that there is insufficient information to evaluate site properly.

(iii) The evidence for the presence of an interior lake is somewhat ambiguous and uncertain.

Nathan Bridges, Crater lakes II: Gale and Meridiani Crater

Meridiani:

Meridiani Crater is located in the heavily cratered terrain, and is surrounded by a number of other large impact craters. It has a central mound deposit, but has substantial problems for its selection as a landing site, primarily in terms of lack of MOC coverage (there are only three images of the interior of the crater).

Gale:

Gale Crater has clearly identifiable layered deposits within its interior, and is thought to have supported an interior lake at some time.

There are three distinct geomorphologic units within the crater interior:

(i) Dark sand dunes.

(ii) Layers on the crater floor.

(iii) Massive layers that form a central mound. These layers are much more massive than and are distinct from the thinner and finer layers on the crater floor. The massive layers stick up above the rim of the crater, and are likely to have formed by a different mechanism than the crater-floor layers. [Note that there are some 95 instances on Mars in which central structures within craters rise up above the height of the crater rim.]

Despite the presence of layers suggesting aqueous activity, the composition of the interior deposits appears to be basalt. Even though layers are present within the ellipse, they are distributed haphazardly and are not likely to be accessible from the rover.

The size of the landing ellipse is a problem for Gale, because the edges include portions of the crater interior wall. Gale is considered as viable from a safety perspective only if the size of the ellipse can reduced from its current size.

Ruslan Kuzmin, Eos Chasma and Northeast Valles Marineris

These two ellipses are in the eastern end of Valles Marineris, in the transitional zone between possible major standing bodies of water in central Valles Marineris and the outflow region. Eos Chasma is in the narrowest region of the outflow, where the "venturi" effect might have resulted in increased flow velocities, and the second ellipse is to the northeast where the flow has had a chance to spread out a bit. Both ellipses are within chaotic terrain, with evidence for subsurface water drainage and local ponding. Layered deposits are identified at the Eos Chasma site.

Remote sensing parameters all seem within acceptable ranges for the two ellipses, although some of the thermal inertia values seem prettyare very high for the Northeast Valles Marineris site.

Because of the location of the ellipses, at the confluence of tectonic and hydrologic activity, these sites have evidence for fluvial-lacustrine activity, mass wasting, sapping, and possible phraetomagmatic processes. As such, they have the potential to provide primary rocks for sampling and analysis, alteration products resulting from aqueous or hydrothermal activity, and sedimentary deposits; in essence, these are "grab-bag" sites that likely will involve evidence for a number of processes. There was some discussion of the MOC images that show predominantly a cratered plains surface.

Athabasca Vallis, Jim Rice

Presentation of a site considered as a low priority until this meeting. Essential characteristics are young volcanic province with high probability of water activity; running water an almost certainty, standing water a possibility, ground ice likely. There is evidence of layering in imagery. Hypotheses to test include whether the province was fluvial, lacustrine, hydrothermal, or simply volcanic.

Meridiani Highlands, Mike Carr

Three areas discussed. Oxia Palus has no MOC coverage and wasn’t considered further. N. Meridiani Sinus appears complex and stripped. This is probably a location with a geologic history too complex to be unraveled with the rover and imagery alone. Meridiani Highlands are Hesperian, ridged, volcanic, and cratered. None of the sites were considered to be worthy of further consideration, especially in light of the fact that their selection would remove the Hematite sites from the list.

Geological Diversity within 500m Radius of Landing Sites, Rob Sullivan

A study of the expected diversity of geologic terrains and questions to address for each landing site. Methodology took existing MOC frames of each priority landing site, randomly selected areas of 1km diameter within each frame, and used subjective, human-based "interest" criteria to determine the expected geologic windfall for each site. Three people independently rated each area; scores were averaged and results presented. In order of most interesting to least: Melas, Gale, Hematite, Gusev, Isidis, and Eos.

Guidelines for the discussion included focus on science potential of the various sites, as safety and engineering constraints and concerns were discussed during afternoon session and included in summary discussion later in the day. Discussion was open-ended, but began with a list of highlights to provide focus.

List included those sites that had received minimal support during workshop:

• Boedikker Crater
  
• EP69A
  
• Meridiani Crater
  
• Ares Vallis
  
• Sinus Meridiani
  
• Highlands Site
  
• Meridiani Highlands
  
• NE Vallis Marineris
  

Sites getting lots of discussion and support (in no particular order):

• Hematite
  
• Melas Chasma
  
• Isidis
  
• Gusev Crater
  
• Gale Crater
  
• Eos Chasma
  
• Elysium Flow (Athabasca Vallis)
  

With that introduction, discussion began:

Jack Farmer: With the Isidis ellipse being north of annulus, what is impact to science?

Larry Crumpler: Not much in an absolute sense, but getting farther from the source increases might decrease the potential to distinguish materials. The current ellipse is out near distal edge of the fan material. If ellipse could be moved to south and east would be better with respect to science potential of the sites.

Ken Herkenhoff: How does the distal contact of the annulus "fan" unit correlate with the location of the ellipse versus the transition to basin fill to the north?

Larry Crumpler: Ellipse is in transition zone between the "fan" and the basin fill to north.

Ken Tanaka: As one movers father to the north, the ability to resolve the context of the materials will be diminished.

Matt Golombek: Can think of the eastern-most Isidis site as a proxy for the science that was hoped for at the site previously proposed for the 2001 mission (in the annulus), which was to access the oldest Noachian material mapped on Mars.

Larry Crumpler: There is evidence for stripping and weathering at the current location of the ellipse, so there has been an extended and complex geologic history.

Mike Carr: We are really looking at seven sites that fall into five categories…

Nathan Bridges: Disagree, crater lakes are different.

Larry Soderblom: But Gale is diminished by inability to accommodate ellipse. By contrast, all ellipses in hematite region are O.K.

General Discussion about whether Gale should be eliminated and what is the significance of the 2 degree limit on slopes over ~1 km length scales. Mark Adler response is that 2 degrees is O.K., but that things continue to roll at 3 degrees. Need more testing to evaluate limits.

Jack Farmer: His perspective: Feels a lot of folks favor the Hematite site because it is interesting mineralogically and geomorphologically and has good synergy with the Athena science package. What worries him is the paucity of lithologic diversity. By contrast, Gusev and Isidis may have good diversity. He would support Eos Chasma as a grab bag site as well, though not as interesting geologically. Gusev and Isidis are the best studied. If one site ends up being Hematite, Gusev or Isidis would be complementary. He would suggest Hematite, and Gusev, and or Isidis would be good.

Jim Rice: Why go for diversity when we tried that at Pathfinder and did not see it?

Jack Farmer: We did not have the tools during Pathfinder, With Athena we do.

Diana Blaney: How do you know if you are going to see diversity at a site? She would like to go to a place where you know that what you are looking at can be placed in geologic context and setting.

Ginny Gulick: The canyon sites could also be considered grab bag sites. Melas Chasma, for example, exhibits albedo variations which may suggest diversity, and because of its location, we may end up sampling the different units making up the canyon walls.

Question to Ruslan Kuzmin: What will we land on in Eos Chasma?

Mike Carr: Diversity is an inference. The hard evidence in the MOC images that we have does not support diversity in Isidis, but does in Melas. Elysium also shows diversity. We see layers in the walls of Valles Marineris, but do not understand their origin. Center part of the Melas ellipse is a jumble of these layers.

Steve Squyres: Notes that Melas is probably the most sensitive of the sites to small changes in targeting (e.g., if there were to be a TCM-6)

Jack Farmer: Could we image the walls of the canyon from Melas?

Steve Squyres: Yes, can get on the order of ~700 Pancam pixels on the walls, but might not be able to do too much science. Might be more of a "scenery" factor. Would not be much better than MOC from above. Would be a good public appeal factor.

Mike Carr: We need to differentiate science versus safety: for safety need to consider entire ellipse. For science, need to emphasize the center of the ellipse.

Matt Golombek: What could we do at Melas?

Ken Tanaka: Multiple ideas posed for origin of canyons. Deposits at the landing sites can provide insight into how these hypotheses could be distinguished.

Steve Squyres: Have on the order of a 73% chance of landing on the layered deposits given the current ellipse in Melas.

Jim Rice: What if Melas is too complicated?

Ruslan Kuzmin: Concerned that eolian sediments may obscure things at Melas.

Matt Golombek: Which of the canyon sites is best?

Jack Farmer: Which canyon site? I’d go to Melas to get samples of wall rock versus going to Eos to get grab bag samples.

Matt Golombek: Feels MOC images show that Eos is a smooth cratered plain. Practically featureless.

Ruslan Kuzmin: Smooth material on floor at Eos site is maybe stable material left behind after floods. Could be fluvially stripped and can also see lake deposits. Don’t know the relationship between fluvial and lacustrine, need more study to evaluate.

General: Agreement that there is evidence for long-term fluvial scour activity at Eos Chasma site.

Jim Rice: What is the evidence for water at the Melas site?

Tim Parker: Small valleys and bright materials interpreted as lake marls.

Alfred McEwen: Not much regolith at the Elysium (Athabasca) site to obscure geology.

Nathalie Cabrol: Not sure if just having evidence for water at a site is enough.

Henrich Wanke: The beauty of the Elysium site is that it is young.

Albert Haldemann: Likes the potential for looking at mineralogy at Elysium and volcano-water interactions.

Jack Farmer: If Elysium is made up of lahars, may not be mineralogically diverse. Might not see evidence for hydrothermal activity.

Matt Golombek: What about trafficability at the Elysium site? Most young lava flows are rough.

Alfred McEwen: The site is not too rough at MOC scale, and flows are actually old and therefore fairly smooth. So probably not to bad getting around with rovers.

Ken Tanaka: With respect to hydrothermal alteration, young volcanics are well exposed, but there may have been much longer-lived systems in the highlands. Only geologically short-term interactions and systems likely in Elysium.

Ginny Gulick: If we are talking about the potential for long-lived hydrothermal systems, we should consider places where there is evidence for repeated magmatic intrusions. We need to also find sites where evidence for past hydrothermal activity and hydrothermal alteration is still exposed or accessible and not buried under meters or more sediment emplaced by other processes.

Henrich Wanke: Feels we should go to Elysium site because it is young and pristine (relatively) and there is good evidence for action by multiple processes.

This afternoon session summarized Landing Site safety issues and various data sets that may be helpful in determining hazards within the landing ellipse. Matt Golombek started the session with a summary of the safety issues. Slopes should be less than 2 degrees on a kilometer scale with 35 meter relief based on MOLA topography and slopes. At the hundred meter scale slopes should be less than 5 degrees with less than ten meters in relief based on the MOLA pulse spread. At the 5 meter scale, slopes need to be less than 15 degrees or less than 1.34 m in relief. The landing site needs to be less rocky than the Pathfinder site.

Mike Shepard gave a talk on RMS slopes derived from MOLA data. MOC is well suited for looking at albedo variations, but because of the 2 PM orbit of the spacecraft, there is not much in the way of shadows to yield information on the topography. Therefore, MOLA is much better for estimating surface roughness. Shepard analyzed the point to point RMS slopes of the potential landing sites at the 300 meter scale and was able to classify their slopes in three groups. Group 1, the smoothest sites, includes all hematite sites and the VL-2 site (the smoothest of all with a RMS slope of 0.7 degrees). Group 2 sites have intermediate RMS slopes. The Pathfinder site at 1.8 degrees, Gale crater at 2.6 degrees, Gusev Crater at 3.4 degrees, VL-1 at 2.5 degrees, and Isidis basin sites at 3.2 degrees are all Group 2. Group 3 contains the roughest of all the sites considered and includes Melas Chasma at 7.2 degrees and Eos Chasma at 7.7 degrees. He also discussed the effect of RMS on profile length. As the scale is increased, the RMS height gets rougher while the RMS slope get smoother. RMS height is defined by e
= e
₀L^H where L is the profile length and e
is the RMS height. RMS slope is defined as s=s₀(D
c
)^1-H where s is the RMS slope and H is the Hurst exponent, which is a measure of the roughness rate. He cautioned to take these numbers in a relative sense only. In other words, group one and two sites are acceptable, group three sites are probably too rough. He commented that the hematite sites are smoother than the landing sites that we are used to seeing and that these sites are all uniformly smooth. The Elysium flow sites are smoother than VL-1, but are rougher than the hematite sites. There was a question as to how his approach in deriving roughness values differs from Garvin’s approach. He stated that Garvin detrends the data where he does not.

Alfred McEwen discussed determining surface roughness via photoclinometry on MOC images. McEwen argued this technique, also known as “shape from shading”, has been given a bad rap based on the understanding that errors in topography are cumulative. McEwen asserted that slope errors are not cumulative and he feels that it is much better than just qualitatively judging roughness. By this method one can derive quantitative upper limits on slope. McEwen determined that Athabasca (Elysium flows) Valles, Eos Chasma, Gale and Gusev crater sites as well as some hematite sites seem ok or “safe”. The remaining sites yielded no useful results. McEwen cautioned to not use the numbers in an absolute sense and to not use this data derived from this approach alone to determine landing site safety. He emphasized that such data should be used with other techniques and that it should be viewed as a reassurance when data from other techniques agrees.

Randy Kirk summarized the methods by which DTM’s (digital terrain models) are derived from MOC stereo images and presented his progress on generating DTM’s for the candidate landing sites. The methodology relies on photoclinometry and stereo analyses of MOC-narrow angle images. He uses commercial photogrammetry software and his own “shape from shading” software. . He discussed several challenges to making DTMs. These include identifying the MOC-NA stereo pairs and adjusting the geometric parameters. He commented that the corrugated nature of the images is due to the high frequency oscillations of the spacecraft and not to anything real in the terrain. Another challenge is characterizing surface roughness. He said direct calculation of slope is time consuming and that Fourier transform techniques are a shortcut to measuring RMS slope at all scales at once. He then summarized his current work on some of the landing sites, emphasizing that using both stereo analysis and photoclinometry (PC) resolves more roughness elements than either technique alone. For example, in determining Melas Chasma slopes, stereo analyses fails to resolve dunes although PC does and therefore gives the best slope estimate. In Gusev, stereo analyses partly resolves the main roughness elements, although PC resolves them better. He commented that the long base slopes were too high, but that some of this is probably due to sampling effects and albedo related artifacts and that slopes are probably about 9 degrees. In Eos Chasma, stereo resolves main roughness elements, and PC confirms that there are no unresolved features. Based on his work so far, he concludes that none of the sites meet the MER engineering requirement of 99% chance of encountering slopes less than or equal to 15 degrees. He stated that he still needs to complete characterization of the landing sites and urged that the rationale for site selection be reevaluated, if his continuing work confirms his preliminary analyses that all the sites are too rough based on the MER engineering safety requirement.

Summary of Day 2 discussions following the afternoon coffee break

Shannon Pelkey, Implications of TES data for Surface Properties and Landing Safety

• I < 100 implies unconsolidated fines


• Presentation gave "degree of concern" for each of the 7 potential landing sites (see viewgraphs from presentation and handout) based on how different the thermal inertia is from those at the three landing sites we have been to.

Scott Nowicki and Phil Christensen, Rock abundance derived from TES data

• I > 1255 implies dense solid rocks 30 cm in diameter.


• TES rock abundance is one observation per pixel while IRTM has observations averaged over ~1 degree — i.e., TES rock abundance has higher spatial resolution (3×6 km TES pixel).


• A series of viewgraphs were shown with rock abundance on TES tracks.


• Premature to rule out any site on basis of TES rock abundance data because of the effect of clouds on the derivation of rock abundance.

Steve Ruff, TES Albedo and Dust Cover Index.

• Dust scale at <1mm depth. Dust index is based on particle size effects (transparency feature) in mid-IR. Uses the region between ~7-8 umm to calculate dust index.


• Dust index has a high correlation with albedo (0.85).


• Hematite region has lowest value of dust index. Melas, VM outflow, and Gale are also not dusty.


• Elysium Flow and Gusev are very dusty. Stay to the west in Isidis.

Matt Golombek, Summary of Landing Site Safety Evaluations

• See presentation viewgraphs


• Only have to worry about I > 600. High values result from duricrust, which is not a landing hazard


• Hematite site is OK on slope and MOLA pulse widths


• Sites with concerns are Gusev (high and bimodal pulse width), Melas (slopes), Isidis (high I), Eos (high I), Central and NE VM (high I), and Elysium Flow (dusty)Of the 7 sites, Gale is eliminated on the basis of slopes.


• Sites with problems are Gusev("out" because of high slopes)


• Note: sites within 37 degrees of Hematite are excluded if that site is chosen.


• What to do with Randy Kirk data. — Albedo variations are interpreted as slope variations. Therefore all measurements are upper limits as discussed by A. McEwen in his presentation. Thus, "warm" feeling when slope values are low and ignore when high. More work needed here.

General Discussion To Select Four Sites — Matt Golombek and John Grant

• The goal of this session is to choose 4 landing sites from the 7 that are viable. If a consensus cannot be reached, the Steering Committee will do the final selection to four sites.


• After discussion on how to proceed, it was decided to vote on the four sites. The votes are summarized in the Table. For Vote #, everyone in attendance could vote for at most 4 sites.

• After Vote #1, the Hematite and Melas sites are selected by consensus.


• Between Votes #1 and #2, the remaining 5 sites (Gusev, Gale, Isidis, Elysium Flow, and Eos) were discussed again. Most discussion centered on Gale, Gusev, and Elysium Flow.


• Elysium Flow: Discussion pointed out evidence for multiple floods, rootless cones. water ponding. There was discussion that this site might not meet mission requirements because it is a young site, might have low astrobiology potential, and might be very dusty (based on bright region and thermal inertial.)


• Gale and Gusev: Discussion was specifically solicited for Gale, as it was felt by some that discussion was prematurely ended earlier because of unfavorable information regarding the safety of the landing ellipse (e.g., slopes too steep within the ellipse for landing). Gale has layer material, which could or could not result from aqueous processes. In Gusev, the photogeologic evidence is that the layering results from aqueous processes.


• Vote #2 was taken after the discussion of the remaining 5 sites ended. Additional discussion was solicited by the discussion leaders, but none ensued.


• The results of Vote #2 are shown in the Table. The selected sites are Hematite, Melas, Gusev, and Elysium Flow. The remaining three sites have backup status. See comments column in the Table for specific information on landing ellipses. The selection of the 4 sites was a genuine consensus among all present.

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