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 TES News.

-- 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
(818) 354-4321




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 km elevation.

Three general types of landing sites were proposed by participants of the workshop:

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.

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:

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).

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!

Sincerely,

Matthew Golombek
Mars Pathfinder Project Scientist
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