Summary of

Pasadena Landing Site Workshop

October 18-19^th^, 2001

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

Edited by J. Grant and M. Golombek

**Session 1 -- Introduction and Overview**

**Provided by** **G. Gulick**

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 \>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 the steering committee. He reviewed the site
selection process 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 provide
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 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 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.

**Session 2 -- Science Potential of the Sites and Discussion Part I**

**Hematite, Melas, and Isidis**

**Provided by K. Tanaka**

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 (00.12), suggesting that little dust is 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.

# Session 3 -- Science Potential of the Sites and Discussion Part II

**Crater Lakes and Eos Chasma**

**Provided by B. Jakosky**

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

Gusev:

Gusev is a 158-km-diameter impact crater, with an estimated 10,000 km^3^
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 are 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.

**Session 4 -- Science Potential of the Sites and Discussion Part III**

**Athabasca, Meridiani, and Highlands**

**Provided by M. Shepard**

# 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.

**Session 5 -- Science Discussion of the Sites**

**Provided by** **J. Grant**

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 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 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: 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 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.

**Session 6 -- Landing Site Safety and Discussion I**

**Provided by G. Gulick**

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 ε =
ε~0~L^H^ where L is the profile length and ε is the RMS height. RMS
slope is defined as s=s~0~(∆χ)^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.

**Session 7 -- Landing Site Safety and Discussion II**

**Provided by R. Morris**

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 (3x6 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 μm 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.

**Session 8 -- Discussion and Prioritization of Landing Sites**

**Provided by R. Morris**

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.

  -------------- --------- --------- --------- --------------------------
  Table. Results                               
  of site                                      
  selection                                    
  votes and                                    
  comments on                                  
  status.                                      

  Site           Type      Vote #1   Vote #2   Comments

  Hematite (SM)  Unique    32        30        Selected site, Ellipse 20B

  Melas          Canyon    30.5      27        Selected site

  Eos            Canyon    8         6         Backup site

  Gusev          Crater    13        23        Selected site, move
                                               ellipse to west into low
                                               albedo material

  Gale           Crater    8         11        Backup, w/ no additional
                                               imaging

  Isidis         Plains    15        14        Backup site, Move ellipse
                                               as far south as possible

  Elysium Flow   Plains    23        24        Selected site. Ellipse TBD

                                               
  -------------- --------- --------- --------- --------------------------

-   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.