Potential landing sites are confined to latitudes between 0 deg and 30 deg N and surfaces below 0 km elevation. The landing ellipse is 100 x 200 km oriented N 74 deg E. The constraints essentially eliminate the slopes of Elysium Mons, Olympus Mons, Tharsis Ridge, Lunae Plaunum, all the southern highlands, and almost all the Noachian material of Arabia Terra. Those areas that remain as potential landing sites are chiefly lowland plains of Amazonis Chryse, Isidis, and Elysium Planitia. Any attempt to sample highland material further constrains the possible landing sites by eliminating areas of Hesperian or Amazonian lavas and sediments. One possible sampling strategy is to sample materials within those few 'highland' terrains that extend to low elevations. A second strategy is to sample materials at the mouth of an outflow channel that drains from the highlands. Potential landing sites include outflow channel material at the edge of Chryse Planitia and highland materials bordering southern Amazonis Planitia

Dehon, Rene A.

English

NASA Technical Reports Server

24 Mars Pathfinder Landing Sire Workshop 
knowledge, then they will be more difficult elsewhere where the 
questions are unknown. 
Conclusions and Site Recommendations: It is tempting to 
set the sights for future prospects on many of the additional interest- 
ing areas defined on Mars since the Viking mission and expand the 
database for ground truth to new and different terrains. This desire 
should be balanced with the critical need for success in planetary 
exploration in general and avoidance of an inconclusive mission 
result in particular. An important goal should be learning how to 
operate on Mars and addressing answerable questions. A f m  start 
on the latter can be attained by a new mission to Chryse Planitia in 
the region specified, in which theexisting ground truth of the Viking 
Lander 1 is used to constrain the engineering choices and to design 
appropriate instrument goals to fully utilize the lander limitations 
and capabilities. Three proposed sites are indicated on Fig. 1 along 
with the currently defined landing ellipses. Site El is most likely to 
be similar to VL-1; site E2 is less well constrained and is likely to 
differ from VL-1 in some respects; and site E3 is likely to be similar 
to VL-1. but incorporates slightly less hazardous, but slightly differ- 
ent terrain. 
[ 11 Crumpler L. S. et al. (1994) USGS 1:1 M scale 
map, submitted. [2] Craddock R. A. et al. (1994) JGR, submitted. 
man s. and Frey J. (1993) Eos, 74, 199. 
References: 
[3] Schultz R. A. and FRY H. V. (1990) JGR, 95, 14175. [4] Stock- 
N95- 16186 
’), A HIGHLAND SAMPLE STRATEGY FOR PATHFINDER. R. A. De Hon, Department of Geosciences, Northeast Louisiana 
University, Monroe LA 71209, USA. 
1 I 
( 
Mission Constraints: Potential landing sites are confined to 
latitudes between Oo and 30°N and surfaces below 0 km elevation. 
The landing ellipse is lOOx 200 km oriented N74OE. The constraints 
essentially eliminate the slopes of Elysium Mons, Olympus Mons, 
Tharsis Ridge, Lunae Plaunum, all the southern highlands, and 
almost all the Noachian material of Arabia Terra. Those areas that 
remain as potential landing sites are chiefly lowland plains of 
Amazonis Chryse. Isidis. and Elysium Planitiae. 
With only two previous Viking landing sites 
in widely separate locations, almost any landing will provide new 
data. Viking I landed on Chryse Planitia on a surface that is 
presumed to be Hesperian ridged plains material, which is inter- 
preted to consist of volcanic flows [ 11. Viking 2 landed on knobby 
material in Utopia Planitia, which is interpreted as eolian and 
volcanic materials (21. The large landing ellipse precludes a finely 
targeted sampling strategy. Several site selection strategies are 
equally valid. Presumably, Noachian materials are more represen- 
tative of the geochemical character of the planet than the volumetri- 
cally less important surficial flows and sedimentary materials. 
Any attempt to sample highland material further constrains the 
possible landing sites by eliminating areas of Hesperian or Amazo- 
nian lavas and sediments. Materials of possible Noachian age are 
primarily located above 0 km elevation and at southem latitudes, 
except for minor occurrences in Arabia Terra and a narrow zone 
along the southern edge of Elysium Planitia. 
One possible sampling strategy is to sample materials within 
those few “highland” terrains that extend to low elevations. Minor 
occurrences of Noachian materials are exposed at low elevations as 
Siting Strategy: 
outliers flanked by younger material within Nepenthes Mensas and 
Aeolis Mensas, but such areas are rugged and unsuitable for a safe 
landing. However, parts of western Arabia Terra extend to accept- 
able elevations and are reasonably smooth. 
A second strategy is to sample materials at the mouth of an 
outflow channel that drains from the highlands. Channels may 
terminate in deltas, alluvial fans, or sheet deposits. For simplicity 
these deposits will be refered to as “fans.” Fans provide materials 
from a large sampling area, and dissected fans offer the advantage 
of providing a vertical section of exposed stratification that records 
the history of the outflow. 
On first appraisal, any fan at the mouth of a channel draining 
from highlands offers a potential target, but not all fans offer equal 
opportunities. Many outflow channels have ponded along their 
length; hence, any sediment carried by the discharge at the mouth is 
derived only from the last site of ponding [3]. Further, although 
catastrophic outflows are characterized by high sediment load and 
large caliper, the last sediments deposited during waning discharge 
are generally fine grained. 
Potential landing sites include out- 
flow channel material at the edge of Chryse Planitia and highland 
materials bordering southern ArnazonisPlanitia. The circum-Chryse 
channels include Kasei Valles into northwest Chryse Planitia; 
Bahram Vallis, Vedra Valles, Maumee Valles, and Ma$ Valles 
into western Chryse; Shalbatana Vallis into southwest Chryse; 
channels draining from Capri and Eos Chasmata into southern 
Chryse (Simud. Tiu, and Ares Valles); and Mawrth Vallis into 
northeast Chryse Planitia. With so many large outflow systems 
terminating within Chryse Basin, it is probable that any landing site 
within the basin (including Viking 1 landing site) will be blanketed 
by sediments from catastrophic outflows or outflow sediments re- 
worked by eolian activity. Channels in southern Chryse Planitia, 
originating within Vallis Marineris or chaotic terrain south of Chryse 
Planitia, traverse Noachian material before entering the basin, but 
they do not provide readily identifiable fans. 
Mawrth Vallis of the Oxia Palus region cuts 
Noachian cratered plateau material, which is interpreted to be 
largely impact breccia of ancient crust [4]. The plateau surface 
bordering the lower reaches of the channel, below 0 and -1 km 
elevation, is one of the few places on Mars where typical highland 
material can be found below 0 km elevation. Three landing sites are 
feasible. One potential site is at the mouth of the channel (29ON. 
21OW); an alternate site is on the plateau surface adjacent to the 
valley (28ON, 18OW); and a third site is south of Mawrth Vallis and 
east of Ares Vallis (2ON, 2OW). The highland site adjacent to 
Mawrth Vallis is more likely to contain less surficial cover than the 
site east of Ares Vallis. If not covered by surfkial material, highland 
sites are likely to consist of highly commuted materials; they would 
provide an estimate of the geochemical character of the homog- 
enized early crust. 
The mouth of Maja Canyon (18ON, S O O W ) ,  with remnant fan 
material cut by late-stage discharges [5,6], offers the best channel 
mouth target. The chief constituents here are likely to be detritus 
from Noachian material of the Xanthe Terra region carried by 
outflow that spilled onto Chryse Planitia following ponding behind 
a barrier massif of Noachian basement material. 
Pitfalls and Predictions: The large landing ellipse and low 
resolution of Viking images do not allow assurance that the landing 
site will contain any particular anticipated material. Extremely 
Potential Landing Sites: 
Best Bets: 
https://ntrs.nasa.gov/search.jsp?R=19950009771 2020-06-16T08:53:33+00:00Z
LPI Technical Report 94-06 25 
localized deposits of young materials are possible in the highlands, 
and mature, winnowed sediments are possible in the plains. Inter- 
pretation of chemical anlyses of fan materials without comspond- 
ing petrologic comparison will be challenging. 
In all probability, the final choice of a landing site will be a level 
lowland within the planatiae. A sedimentary surface of an essen- 
tially monomineralic, eolian (sand or loesslike) material or a lacus- 
trine deposit should not be a surprise. 
References: [ I ]  Scott D. H. and Tanaka K. L. (1986) USGS 
Misc. Inv. Ser. Map I-1802-A. [2] Greeley R. and Guest J. (1987) 
USGS Misc. Inv. Ser. Map 1-1802-8. [3] De Hon R. A. and Pani 
E. A. (1993)JGR, 98,9129-9138. [4] WilhelmsD. E. (1976)USGS 
Misc. Inv. Ser. Map 1-895. (51 Rice J. W., this volume. [6] Rice J. W. 
and De Hon R. A. (1994) USGS Misc. Inv. Ser. Map I-2432. 
? 
., / /' . 
\ 
- / J  N95-16187 
' OPPORTUNITY TO SAMPLE SOMETHING DIFFERENT: 
BERUS AND THE PATHFINDER 1997 MARS LANDING. 
K. S. Edgettl, R. B. Singerz. and P. E. Geissler2, 'Department of 
Geology, Box 87 1404, Arizona State University, Tempe AZ 85287- 
1404, USA, *Planetary Image Research Laboratory, Department of 
Planetary Sciences, University of Arizona. Tucson AZ 85721, USA. 
THE DARK, UNWEATHERED, MAFIC SANDS OF CER- 
Dark Material Critical to Understanding Mars Surface: A 
very important surface component, typically described as "dark gray 
material" [ 11, was not seen at the Viking lander sites, but is common 
to all low-albedo regions on Mars. Dark material probably includes 
unaltered mafic volcanic and/or crustal rock and soil not coated by 
dust, weathering rinds, or varnish [2). 
A Pathfinder landing in Cerberus (9"N- 16'N. 194OW- 2 15"W) 
will guarantee examination of materials that are distinctly different 
from the two Viking lander sites. In  situ study of dark material will 
provide vital ground truth for orbiter-based observations like those 
anticipated from Mars '941'96 and Mars Global Surveyor. 
Surface Properties and Regional Context: The Cerberus 
region is (1) not as rocky as the Viking sites, (2) not blanketed by 
dust, and (3) offers sampling of a range of rock and soil types 
including iava flows of different ages, ancient crustal rock. dark 
sand, bright dust, and possible fluviolacustrine materials. Cerberus 
lies between 0 and -1 km elevation ( f l  km; USGS 1991 topogra- 
phy), and is large enough to meet our main objective within the 
landing ellipse constraints. Cerberus is an active eolian environ- 
ment, but major dune fields are absent and activity is not as vigorous 
as in Syrtis Major [3]. The landing will occur in northem summer, 
a period when predicted winds are not at their strongest in the region 
[41. 
The dark surfaces have low albedos (4 .15 )  and intermediate 
thermal inertias [5]  (300-400 J m-2 ~ 4 . 5  K-1). which indicate that 
much of this material is sand (100-lo00 pm). Rock abundance [6] 
varies from -12% in the east, where the surface has many knobs and 
mesas, to -1 9% in the west, with average over most of Cerberus -7%. 
(Viking 1 rock abundance was -10% and Viking 2 was -20% [SI). 
The dark soil of Cerberus is superposed on several different 
geomorphic features. Central and western Cerberus is underlain by 
Early Amazonian volcanic flows originating on the Elysium Rise 
[7]. Cerberus is bounded in the south and east by interpreted paleolake 
deposits [7,8] and very recent (0 to 700 Ma) lava flows [9]. Eastern 
Cerberus includes a smooth surface of Late Amazonian fluvial, 
lacustrine, andor volcanic deposits 17-91 and Noachian(?) mesas 
and knobs of the Tartarus Colles [7]. 
Dark Material and Source: Dark sand has been transported 
through and deposited within Cerberus [3,10,11]. Lateral variation 
in sand deposit thickness is probable, with sand filling low areas on 
and between lava flows. Dark material has blown from east to west 
over the lava flows of southern Elysium, perhaps making Cerberus 
similar to the Amboy volcanic field of Southern California. Amboy 
has lava flows overlain by windblown sand stripped from an upwind 
dry lake [ 121. 
Dark material might be eroded from sediments of the proposed 
lacustrine basin [SI east of Cerberus. Alternatively, the sand may 
have avolcanic source, perhaps pyroclastic material from the Elysium 
volcanos or from eruptions along the Cerberus Rupes fractures. 
Dark material appears to emanate from some Cerberus Rupes frac- 
tures ([ 1 11. Viking image 883A09). Do the fractures expose a layer 
of dark material that is now eroding [IO, 1 l]? Did dark material from 
the east fill the fractures. and now is being deflated? Or were the 
fractures the sites of pyroclastic eruptions? One fracture seen in the 
upper left corner of Viking frame 385823 has a dark, semi-elliptical 
mantle deposit similar to pyroclastic deposits on the Moon and Io. 
Pathfinder Science: Cerberus is large enough that several 
landing sites could be chosen. Although any landing in Cerberus 
will satisfy our main objective. we suggest asite near 13"N. 200.5"W 
(see Viking frame 883A06), because it has both dark material and 
proximity to the three major geomorphic units in the region (lava 
flows, possible lake sediments, and knobs of ancient crust). In 
addition, at this site there is adark lobe that appears to emanate from 
a Cerberus Rupes fracture (Viking frames #883A04-06) that might 
be one of the youngest, unaltered lava flows on Mars. Although not 
reporting on this specific flow,Plescia (91 proposedthat the Cerberus 
Rupes were the source of some very young lava flows (400 Ma). 
The main objective for a Cerberus landing will be to determine 
the composition and physical properties of dark soils thought to be 
derived from unaltered primary igneous crustai material. Character- 
ization of the size, shape, and mineralogy of dark grains 0.1 mm to 
IO cm will allow assessment of sediment maturity. Is martian sand 
formed of ancient, resistant mineral grains or fresher, easily altered 
material? The answer to this question will place constraints on 
chemical weathering and eolian abrasion rates. Bright wind streaks 
in the lee of craters in Cerberus suggest that dust might also be 
available for sampling, particularly in the lee of meter-scale ob- 
stacles. Finally, the presence of sand or granule wind ripples would 
provide insight into the nature of surface-atmosphere interactions 
on Mars. 
[ 1) Arvidson R. E. et al. (1989) JGR, 94, 1573- 
1587. [2] Singer R. B. et al. (1979) JGR, 84,8415-8426. [3] Lee 
S. W. (1986) L P I  Tech. Rpt. 87-01, 71-72. [4] Greeley R. et al. 
( I  993) JGR, 98.3 183-3 196. [5] Christensen P. R. and Moore H. J. 
(1 992) inMars, 686-729, Univ. of Arizona,Tucson. [6] Christensen 
P. R. (1986) Icarus, 68, 217-238. [7] Tanaka K. L. et al. (1992) 
USGSMap1-2147. [8] ScottD.H.andChapmanM.G.(1991)Proc. 
LPS, Vof. 21,669-677. [9] Plescia J. B. (1990) Icarus, 88,65490. 
[lo] Head 3. N. et al. (1991) BAAS, 23, 1176. [ l l ]  Head J. N. et al. 
(1992) LPS XXlII, 509-510. [I21 Greeley R. and Iversen J. D. 
(1978) in Aeolian Features Southern California: A Comparative 
Planetary Geology Guidebook, 23-52, NASA. 
References: 


A highland sample strategy for Pathfinder

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