MARS PATHFINDER Landing Site Selected
The Mars Pathfinder Landing Site has been selected. The letter below
was written by Dr. Matt Golombek, Project Scientist for the Mars Pathfinder
mission. In this letter, Dr. Golombek reveals some information
about how and why the landing site was chosen.
More information about Mars Pathfinder and the landing site selection process
can be found in a summary of the April 18-19, 1994, Mars Pathfinder Landing Site
Workshop. This summary is in a technical report available from the Lunar and
Planetary Institute of Houston, Texas. The letter below accompanied the intial
mailing of this report to participants in the April workshop.
To obtain the report:
"Mars Pathfinder Landing Site Workshop"
LPI Technical Report 94-04
Lunar and Planetary Institute
3600 Bay Area Boulevard
Houston, Texas 77058-1113, U.S.A.
(they will charge for shipping and handling)
The letter below is not included in the printed report, but was mailed
as a cover letter. For other news about the Pathfinder landing site
selection, see our
August 1994 issue of
-- K.S. Edgett, Arizona Mars K-12 Education Program, 9 August 1994
Jet Propulsion Laboratory
California Institute of Technology
4800 Oak Grove Drive
Pasadena, California 91109-8099
June 20, 1994
Dear Mars Pathfinder Landing Site Workshop Participant:
I want to thank you all for participating in the Mars Pathfinder Landing Site
Workshop held at LPI April 18-19, 1994. Virtually everyone I have spoken with
has said how much they enjoyed the workshop. The workshop and the discussion
session at the end of the second day helped tremendously in narrowing down the
types of landing sites. Given that the workshop technical report is now being
distributed, I thought I would take this opportunity to explain the subsequent
landing site selection process and the landing site chosen for Pathfinder.
First let me provide some general observations about the meeting that helped in
the selection. There was no unanimous first choice landing site for all
participants. In other words, there was no "dinosaur bone site" on Mars that
all felt was so compelling that Pathfinder had to go there. Second, virtually
all types of landing sites proposed are available within the preferred
constraints of being within 5 degrees of 15 degrees north latitude and below 0
Three general types of landing sites were proposed by participants of the
In general, it seemed that many of the attendees and the various science
disciplines represented were supportive of a "grab bag" site that holds the
prospect of learning the most about what Mars is made of. These sites are all
located where catastrophic flood channels debouch into Chryse Planitia and have
cut through a variety of ancient Noachian crustal units as well as the Hesperian
Ridged Plains and a variety of other units. The potential of analyzing a
variety of rocks that likely make up 2/3 of the crust of the planet, even
without knowing their provenance exactly, is an exciting prospect for the next
landed mission to Mars. What makes this type of site potentially more
interesting than simply landing in the highlands themselves is the possibility
of sampling more different highlands materials than might be accessible
otherwise. These sites are likely similar to the Viking 1 landing site: both
rocky and dusty.
- "Grab Bag" Site - a place such as the mouth of a large catastrophic outflow
channel in which a wide variety of rocks are potentially available and within
reach of the rover. Even though the exact provenance of the samples would not
be known, the potential for sampling a large diversity of martian rocks in a
small area could reveal a lot about Mars overall. Data from subsequent orbital
remote sensing missions would then be used to infer the provenance for the
"ground truth" samples studied by Pathfinder.
- Large Uniform Site (at Viking resolution).
- Large Uniform Site of Unknown Rock Type. The site appears uniform at Viking
resolution, but the interpretation of rock type or composition of the unit is
uncertain. Landing at the site would allow determination of the rock type that
makes up the unit. Several of these sites were presented and received strong
support at the workshop.
- Large Uniform Site of Suspected or Known Composition, such as a lava flow.
Landing at such a site would confirm the rock type and measure something about
it that was important (e.g., iron and magnesium content of a basalt).
The other area of interest to a variety of scientists was the Cerberus region.
This area holds the potential of sampling a widespread low-albedo surface eolian
unit, interpreted in this area to be mafic sand. In this region, a variety of
different crustal units are available, including what may be unweathered
highlands material. This area will likely look different from the Viking
landing sites, being relatively rock-poor and dust free. Going to sample this
dark eolian unit is equivalent to going to a large uniform site of unknown
origin to find out what the unit is.
A smaller group of scientists wanted to go to sediments; unfortunately uniquely
identifying sediments from Viking images is difficult and it would be difficult
to be sure that the desired sediments would be within reach of the rover after
landing. In addition, Pathfinder's instruments are much better suited to
determining the mineralogy of rock rather than soil.
In general, few scientists present were very excited about landing at a large
uniform site of suspected known composition, given that this effectively
involves going to a basalt flow (one of the few rock types on Mars identifiable
from orbit). This was underscored by the widely accepted hypothesis that we
already have samples of young basalts from Mars in the form of the SNC
meteorites. Going to Mars to confirm that the SNC meteorites are, in fact, from
Mars did not get much support at the workshop. Taken one step farther, this led
many to conclude that sampling ancient crust is potentially more compelling than
trying to sample other materials, given that the highlands represent most of
what Mars is made of and likely record first order processes such as planetary
differentiation. In addition, we have virtually no knowledge about what a
highland surface looks like, or what processes dominated in its formation
(topics that could be addressed by a Pathfinder landing).
Given these general guidelines, the following decisions were made to narrow down
the selection. First, all the sites proposed at the Landing Site Workshop were
plotted on the 1:15M geologic maps. All sites above 0 km elevation or outside
of 10-20 degrees north latitude (i.e., 5 degrees around the sub-solar latitude
of 15 degrees north, required for maximum solar power generation) were omitted.
If a proposed site fell outside this latitude band, it was moved within the band
if the same general geologic unit was available. In addition, a few other sites
that are within the engineering constraints and have preferred science
attributes expressed at the workshop were added. (Examples are ridged plains
and highland sites with low-albedo eolian cover). All sites within radar
stealth regions or with very low thermal inertia (Unit 1 of Christiansen and
Edgett, abstract) were omitted on obvious safety grounds. This left about 10
sites that fit all the constraints. These sites were then prioritized into two
categories based on science rationale and safety considerations from a
preliminary assessment of the MDIM data base and surface hazard data (e.g.,
radar, thermal inertia). The first group includes two grab bag sites in outflow
channels that debouch into Chryse and two highland sites (one with low-albedo
eolian cover, one densely covered with a valley network). The second group
consist of sites of large uniform material of essentially unknown composition.
These sites include other highlands, ridged plains and young channel/lava sites.
Unfortunately, no site provides both a grab bag of ancient Noachian material and
dark eolian material.
The top four sites were carefully evaluated using virtually all available data
and models including: Viking images, thermal inertia, rock abundance, albedo,
radar, color, occultation data, and weather data from Viking measurements and
atmospheric models. (We gratefully acknowledge data and analyses by non-science
team members P. Christiansen, ASU, M. Slade, JPL, and D. Smith and M. Zuber,
GSFC). All data were presented and discussed at the June 9-10, 1994 meeting of
the Mars Pathfinder Project Science Group. Final selection was made by a
democratic vote of all attending science team members.
The Pathfinder Landing Site selected is:
Radar data will be collected in this latitude band from the end of 1994 through
early 1995. If the radar data show a surface considered dangerous for
Pathfinder landing, the following alternate sites will be considered:
- (#1) Ares/Tiu Valles (19.5N, 32.8W, -2 km elevation) - This site is a grab bag
site with the potential for sampling a variety of Noachian plateau material
(aka, ancient crust) as well as Hesperian Ridged Plains and a variety of
reworked materials. It is about as rocky as the Viking sites, but perhaps a bit
less dusty. This site has clear streamlined islands nearby and a very smooth
depositional surface at Viking resolution (order 30 m/px), except for large
(hundreds of meters) blocks or hills.
Other potential Pathfinder landing sites that were eliminated during the
selection process are listed below (in no particular order). All are large
uniform sites of unknown composition (except for the Elysium lavas site, which
is a large uniform site of known composition).
- (#2) Oxia Palus Dark Highlands (somewhere between 10N-17N, 11W-20W, and at <0 km
elevation) - This is a site extracted from the desire expressed at the workshop
to sample ancient highland crust and the desire to sample dark surficial/eolian
deposits. The exact location of the landing ellipse is still being worked, but
the attempt is to place the entire ellipse in dark eolian material that is below
0 km elevation, with reasonably high-resolution Viking images.
- (#3) Maja Valles Fan (18.8N, 52W, -0.5 km elevation) - This site is also a grab
bag site with similar sampling opportunities as site 1. A delta/fan is fairly
clearly exposed at the location, although the landing ellipse can not be fit
entirely on it. An ancient highland massif just above the fan could improve the
likelihood of sampling ancient crustal material.
- (#4) Maja Highlands (13.5N, 53W, 0 km elevation) - We added this site because it
would sample an ancient highlands region cut by a plethora of valley networks.
Landing at this site would not only sample the highlands of Mars, general
observations of the local area could help determine whether the valley networks
resulted from rain or sapping, which has paleoclimatic implications. Overall
the site appears fairly smooth at Viking resolution, except for a number of
eroded craters. It is just to the south of the Maja fan/delta site.
All of us involved in the selection process were happily overwhelmed by the
number of interesting and exciting sites for landing on Mars. Once again, thank
you for your participation in the Landing Site Workshop. I hope you will share
in the excitement of exploring the surface of Mars in 1997 with Pathfinder!
- Dark Hesperian Ridged Plains (14N, 243W) - This site was added after the
workshop to sample the important martian geologic unit known as ridged plains
and dark eolian surface material. The site appears smooth in available Viking
images, with few wrinkle ridges, giving it a very uncharacteristic appearance
for ridged plains.
- Marte Vallis (17N, 176W) - This area was suggested by a number of
participants at the conference. At this location Pathfinder would sample either
a young channel or young basalts. If it sampled channel material the sediments
in the channel would be Hesperian and Amazonian in age.
- Hypanis Valley Network (11.5N, 45.5W) - This site is sort of a hybrid, which
includes a grab bag of the local highlands at the mouth of a highlands valley
network channel system. Rocks are likely to be more locally derived than for a
large outflow channel. The site is a fairly smooth depositional surface with
some knobby terrain in the eastern part of the ellipse. Unfortunately, high
resolution Viking imagery is not available for this site.
- Isidis Planitia (15N, 275W) - This site was proposed at the workshop to
sample late Hesperian plains sediments.
- Tartarus Colles (11.5N, 198W) - This site samples both Hesperian/Noachian
material and the dark eolian material. At the available Viking imagery coverage
(moderate resolution only) the site appears very rough - a mass of knobs.
- Elysium Lavas (13N, 203W) - This site was proposed to sample known Elysium
lava flows. It is also in the dark eolian cover.
Mars Pathfinder Project Scientist
Text provided here as a service of the