A Mars Pathfinder landing site in Melas Chasma (Valles Marineris) would yield significant science return, but is outside present mission constraints. In Melas Chasma, Mars Pathfinder could investigate minimally altered basaltic material, sedimentary deposits, chemical weathering, tectonic features, the highland crust, equatorial weather, and Valles mists. Critical issues include the following: (1) nature and the origin of the Valles interior layered deposits, important for understanding water as a sedimentary and chemical agent, and for the past existence of of environments favorable for life; (2) compositions of little-altered basaltic sands, important for understanding magma genesis and weathering on Mars, and the martian meteorites; and (3) structure and composition of the highland crust, important for understanding Mars' early history 

Murchie, Scott

Treiman, Allan H.

English

NASA Technical Reports Server

LPI Technical Report 94-04 41 
. 
c 
IMP provides the geologist, and everyone else, a view of the local 
morphology with millimeter- to meter-scale resolution over a broad 
area. Accurate ranging to local features is obtained with the stereo 
separation; at a distance of 5 m we can locate a rock to 1-2 cm by 
cross-correlating edge features. In addition to the general morphol- 
ogy of the locale, IMP has a large complement of specially chosen 
filters to aid in both the identification of the mineral types and their 
degree of weathering. Dr. Robert Singer will present both the filters 
and the scientific goals for this part of the IMP experiment in his 
talk. 
The IMP team plans to study the atmosphere in several ways. 
Our baseline filter set includes three solar filters for viewing the 
solar disk. One of these filters is specially designed to be centered 
on the deepest lobe of the 935-nm water absorption band; an adjoin- 
ing continuum filter provides calibration reference. ‘Ihe ratio of the 
two filters is obtained many times during the course of the day, 
especially when the Sun is low in the sky and the absorptive path is 
longest. Although the ratio is estimated to be only 0.98-0.99 for 
nominal water vapor values, we have gone to great pains to mini- 
mize systematic errors, and it is anticipated that the water vapor 
mixing ratio can be obtained to within 20%. 
An additional solar filter at 425 nm has been added for studying 
the optical depth of the atmospheric dust. The wavelength baseline 
when combined with the 925-nm continuum filter is a factor of 2; 
sizes can be accurately obtained for dust particles less than 1.4 pm 
in diameter by comparing the ratio of optical depths in the two colors 
to Mie scattering models. The nonsolar filters can also be used for 
studying the scattering of sunlight from the sky. In this way, the 
phase function of the dust can be determined and the sizes of larger 
particles can be estimated. These experiments can be continued into 
the night by observing Phobos. Other experiments to leam about the 
atmospheric dust can be easily imagined. 
Not only can IMP observe the dust in the sky, we can trap the 
magnetic portion of that dust onto a series of magnetic targets of 
varying strength. Dr. Jens Martin Knudsen of the University of 
Copenhagen in Denmark has developed a special set of targets for 
the Pathfinder Mission and has shown in the laboratory the useful- 
ness of imaging these targets with the IMP spectral filters to identify 
which magnetic mineral he has captured. In addition to the spectral 
TABLE 1. 
Parameter IMP Viking 
IFOV (1 pixel) 
Frame size 
Depth of field 
Exposure time 
minting 
Stereo 
Height above surface 
Bits per pixel 
Filten 
Filterbandpass 
Camera step size 
Pointing repeatibility 
0.057’ ( I  mrad) B&W. 0.04’ 
Color: 0.12’ 
14.4’ x 14.4’ line scan 
0.6 m - inf 1.7 m-  inf 
0.5 m~ - 32 s 0.4ms or 25 ms 
-65’ e elevation e +W -600 e elevation e +32O 
All azimuthangles 2.5’ e AZ < +342.5’ 
I5 cm horizontal 80cm horizontal 
76 cm vertical limited field 
1.4m 1.3m 
12 6 
12pereye 6 
4oNntYP 100 nm 
1.125’ both EL and AZ 
0.09’ at any step position 
information, the magnetic strength of the material can also be 
determined by seeing which targets have trapped the dust. We 
currently plan for two sets of targets at different heights: close to the 
surface and about 0.5 m above the surface. 
A final aspect of IMP related to atmospheric studies is the wind- 
sock experiment. Dr. Ronald Greeley of Arizona State University is 
developing and testing small telltales to be place at varying heights 
between the surface and 0.5 m on one of the antennae. By imaging 
these targets, both the direction and velocity of the wind can be 
estimated. Calibration is being done at the Ames Martian Wind 
Tunnel, where pressure and wind speeds can be simulated; of 
course, the gravity must be scaled. By including wind socks at 
several heights the local aerodynamic roughness of the terrain can 
be determined and the winds can then be accurately extrapolated 
above the lander site. Viking landers had wind measurements at 
1.6 m above the surface only; extrapolation to other heights was very 
uncertain. 
? 
I ”  
N95- 16207 
/ i--- / / / 
MELAS CHASMA: A MARS PATHFINDER VIEW OF 
VALLES MARINERIS. A. H. Treiman and S. Murchie, Lunar 
and Planetary Institute, 3600 Bay Area Boulevard, Houston TX 
77058-1 1 13, USA. 
A Mars Pathfinder landing site in Melas Chasma (Valles Mar- 
ineris) would yield significant science return, but is outside present 
mission constraints. In Melas Chasma, Mars Pathfinder could in- 
vestigate minimally altered basaltic material, sedimentary deposits, 
chemical weathering, tectonic features, the highland crust, equato- 
rial weather, and Valles mists. Critical issues include ( I )  nature and 
origin of the Valles interior layered deposits, important for under- 
standing water as a sedimentary and chemical agent, and for the past 
existence of environments favorable for life; (2) compositions of 
little-altered basaltic sands, important for-understanding magma 
genesis and weathering on Mars, and the martian meteorites; and 
(3) structure and composition of the highrand crust, important for 
understanding Mars’ early history. Data from Melas Chasma would 
provide ground truth calibration of remote sensing datasets, includ- 
ing Phobos ISM. 
In the first workshop circular, the 
landing site was to be “roughly between the equator and 30°N with 
a “landing . . . uncertainty of roughly 150 km.” In the final circular, 
the landing site is restricted to “OON and 30”N.. . within a 100- 
km x 200-km ellipse along a N74E axis around the targeted site . . .” 
No hazard-free nominal site in Melas Chasma satisfies these later 
criteria. However, a hazard-free restricted site to 85 x 170 km at the 
same orientation can be accommodated (Fig. I ) .  
Site. The proposed landing site is at 9.75s 72.75W in Melas 
Chasma, the widest portion of Valles Marineris [I-31. The re- 
stricted site (Fig. 1) is a flat, smooth surface, -2 to +1/2 km in 
elevation, mapped as younger massive material [ 1,2]. This surface 
is probably composed of basaltic sand, very slightly hydrated and 
oxidized. A thermal inertia of 8-10 x le3 cal cm-2s-1’2K-t 141 and 
block abundances of 510% [SI suggest sand with scattered blocks 
(fewer than at VLI) and little dust. A surface of slightly altered 
basalt or basaltic glass [6] is suggested by its dark (albedo 0.18-0.2) 
and slightly reddish color [4,7], its abundance of high-Ca pyroxene 
[8], and the presence of H,O but little structural OH [7]. 
Mission Constraints I: 
https://ntrs.nasa.gov/search.jsp?R=19950009792 2020-06-16T08:53:07+00:00Z
42 Mars Pathfinder Landing Site Workshop 
North and east in the restricted site are rough floor material and 
landslide material [I], the smooth distal tongues of landslides. In the 
nominal site, but not the restricted site, are mesas of layered mate- 
rial, probably volcanic or lacustrine sediments [ 1,9]. Mesa eleva- 
tions axe to 2.5 km, and some are bounded by cliffs. 
Surface. Imagery of the landing surface will help elucidate 
recent surface-atmosphere interactions (wind) and past geological 
processes in Valles Marineris (sedimentary or volcanic deposition, 
erosion by wind and water). Characterization of the landing surface 
will provide ground-truth calibration for remotely sensed data from 
Viking color and IRTM, Phobos 2 ISM, and Earth-based spectros- 
copy and radar. 
Sand, rocks, and dust should be accessible. The sand has little 
adhering dust [a], so IMP and APXS analyses of sand will include 
little dust component, Data on the sand, if basaltic, will help explain 
martian magma genesis and volcanic processes, provide tests of the 
origins of “martian” meteorites (via element abundance ratios [IO]); 
and provide clues to aqueous alteration processes (especially from 
IMPspectra). Rocks on the landing surface probably represent local 
types, including basalt, sediment (layered material), and highland 
material from Chasma walls. Chemical and spectral data on rocks 
will be important in elucidating the geologic history of the Valles 
Marineris area, and will be relevant to all sedimentary, highlands, 
and volcanic terrains on Mars. There will likely be local concentra- 
tions of dust for analysis. 
Scene. The IMP will have spectacular views of Chasma walls to 
the north (-5.5’ vertical angle, 101 IMP pixels, 60 &pixel) and 
mesas of layered material to the southwest (-1.5’ vertical angle). 
Spectra from IMP will help reveal the mineralogies and composi- 
tions of highland crust (in Chasma walls). LunaelSyria Planum 
resurfacing units, layering at tops of the Chasma wall, and the 
sedimentary layered material. IMP and synthetic stereo imagery 
will help clarify structures, material properties, and slope processes 
of the Chasma walls; tectonic structures in and around Melas; and 
stratigraphic, depositional, and exobiological implications of lay- 
ered Valles fill. 
Atmosphere. Meteorological data from Melas Chasma would 
be the first from an equatorial site, but local effects could be 
significant. Valles mists could be studied directly, and the Chasma 
wall and mesas could provide some calibration for airmass optical 
depths as a function of elevation, at least to the wall heights. 
Mission Constraints II: To investigate Melas Chasma re- 
quires landing at IO’S, entailing decreases of -10-158 photovol- 
Fig. 1. Nominal and restricted landing ellipses (100 x 200 km and 75 x 
150 km) proposed for Melas Chasrna. Scene is 8 to 12s. 67.5-80W. ellipses 
centerednear9.753,72.75W. 
taic power (vs. 15’N). and -1 hdday line-of-sight with Earth (vs. 
O’N) [ 1 I]. To maintain safety, a landing ellipse with an aspect ratio 
of 2 1 and elongation on N74E must be c -170 x 85 km. Ellipses of 
100 x 200 km aligned between east-west and -S30°E can be 
accommodated in Melas Chasma with no elevation above about 
1 km. 
[ I ]  Witbeck et al. (1991) USGS Map 1-2010. 
[2]Puelvast and Masson (1993) Earth, Moon, Planers, 61, 219. 
[3] Lucchitta et al. (1994) JGR, 99,3787. (4) Palluconi and Kieffer 
(1981) Icarus, 45, 415. [SI Christensen (1986) Icarus, 68, 217. 
[6] Murchie and Mustard (1994) LPSXXV, 955. [7] Murchie et al. 
(1993)Icurus, 105,454. [8]Erardetal. (1991)Proc.LPS, Vol.21, 
437-455; Murchie et al. (1993) LfS XXN, 1039. [9] Nedell et al. 
(1987) Icarus, 70, 409; Komatsu et al. (1993) JGR, 98, 1 1  105. 
[IO] Treiman et al. (1986) GCA, 50, 1071; Lindstrom et al. (1994) 
LPS XXV, 797. [ 1 I] The Astronomical Almanac (1994) U.S. Govt. 
Printing Office. 
b 
References: 
.a - 
-.J + 
./ N95- 16208 ). 
CLIMATOLOGICAL TARGETS FOR MARS PATHFINDER. 
A. P. a n t ,  SETl Institute, NASA Ames Research Center, Moffett 
Field CA 94035. USA. 
Major Climatological Questions: Did Mars have awet. warm 
climate early in its history? There is evidence that water flowed 
across the martian surface during the Noachian [ 11, and a hydrologic 
cycle was probably required [2]. However, surface temperatures 
early in martian history are predicted to have been too low for liquid 
water [3]. An atmospheric greenhouse, with CO, as the major 
constituent, has been postulated as a mechanism to raise surface 
temperatures. The subsequent fate of that C02 remains a puzzle; 2- 
5 bar would have been required, equivalent to a global layer of 
calcite 46-1 15 m thick. Although bulk carbonates have recently 
been reported in martian meteorites [4], it is important to search for 
in situ martian carbonates. 
Did the discharge of martian outflow channels produced a large 
Ocean in the northern plains, and Hesperian and Amazonian periods 
of clement climate? It has been hypothesized [SI that return of CO, 
to the atmosphere could have Occurred during the creation of the 
outflow channels, and that subsequent higher surface temperatures 
could have permitted a global hydrologic cycle that was responsible 
for formation of a vast Austral ice sheet. The outflow would have 
formed a northern Ocean that would eventually have reprecipitated 
the CO, into carbonates, thereby ending the warm, wet periods. 
Is chemical weathering proceeding at present on Mars? The 
reactive nature of regolith materials suggests either that reactive 
oxidants are present in the soil [6], or, more likely, that heteroge- 
neous chemistry is taking place between surface materials and 
photochemically produced oxidizing compounds in the atmosphere 
171. 
Target Considerations: Theability tolook into the pastmeans 
the ability to look down the sedimentary sequence. The ideal land- 
ing site is one in which sedimentary units are exposed. Ideally, a 
mixture of clastic and chemical sediments will be present; decime- 
ter-scale coherent igneous rocks would provide the opportunity to 
examine chemical weathering processes. A near-shore deposit, 
where local channels show evidence of having dissected units of a 
variety of ages, would be ideal. 


Melas Chasma: A Mars Pathfinder view of Valles Marineris

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