The northwest Isidis Basin offers a unique opportunity to land near a fretted terrain lowland/upland boundary that meets both the latitudinal and elevation requirements imposed on the spacecraft. The landing site lies east of erosional scarps and among remnant massif inselbergs of the Syrtis Major volcanic plains. The plains surface throughout Isidis exhibits abundant, low-relief mounds that are the local expression of the 'thumbprint terrain' that is common within a few hundred kilometers of the lowland/upland boundary. The massif inselbergs are not as numerous nor as massive as those fretted terrains to the northwest, so local slopes are not expected to be steep. Neither feature should pose a serious threat to the lander. Landing on or adjacent to one of these features would enhance the science return and would help to pinpoint the landing site in Viking and subsequent orbiter images by offering views of landmarks beyond the local horizon

Parker, Tim J.

Rice, Jim W.

English

NASA Technical Reports Server

34 Mars Pathfinder Landing Site Workshop 
14 N95- 161 96 
SCIENTIFIC RATIONALE FOR SELECTING NORTHERN 
LONGITUDE) AS A POTENTIAL MARS PATHFINDER 
LANDING SITE. T. J. Parker, Jet Propulsion Laboratory, 
California Institute of Technology, Pasadena CA 91 109, USA. 
EUMENIDES DORSUM (9O-ll’N LATITUDE, 159”-162” 
The proposed site is the northernmost occurrence of the Medusae 
Fossae Formation (MFF), and lies at or below the -2-km contour. 
The MFF is the famous radar “stealth” deposit that extends from 
south of Olympus Mons westward across southern Amazonis Planitia 
to southern Elysium Planitia. The MFF appears to be composed of 
some kind of wind-eroded friable material, the origin of which is 
very problematic. It appears to be a radar-absorbing material [I], 
whereas Mars’ south polar layered deposits appear bright in the 
same scenes. Synthetic aperture radar images of young terrestrial 
ash deposits in the Andes also appear relatively bright. The MFF’s 
radar signature appears to require a uniformly fine-grained material 
(on the order of dust-sized to fine sand-sized) at least several meters 
thick, in order not to transmit reflections off underlying terrain or 
internal reflective horizons. A number of very different hypotheses 
have been proposed over the years to explain this formation. It has 
been interpreted as either a large, wind-blown volcanic ash deposit 
[2] or other wind-blown material trapped along the escarpment 
between highlands and lowlands [3,4]; ancient polar layered depos- 
its [SI requiring a massive change in the planet’s rotation axis; and 
finally as carbonate platform deposits [6] or banks of low-density 
volcanic material deposited in an Ocean [71. 
Accumulation of tens to thousands of meters of unwelded, fri- 
able ash blankets, necessary to avoid formation of internal reflec- 
tors, would seem to require a large number of discrete, relatively 
thin deposits. The radar signature, therefore, seems inconsistent 
with the volcanic ash and polar layered material interpretations. The 
“stealth” requirement may be met by an uncemented sand or loess 
material, thus supporting the suggested eolian hypothesis. It might 
also be met by inferring chemically precipitated but largely 
uncemented carbonates. If correct, this last model would have 
important implications with regard to search strategies for fossil 
organic materials or the environments that might be conducive to 
their development. In 199 1, I suggested that the surface morphology 
of the MFF is comparable to terrestrial carbonate platform deposits 
[6]. The best modem analogs would be oolitic deposits, such as 
found over large regions of the Bahama Banks. To fit the observed 
morphologies and radar signature, a process akin to inorganic oolite 
precipitation and transport by oceanic currents or agitation by waves 
[8,9], with little cementation, was proposed. An oolitic grain size is 
necessary both to provide the “stealth” radar signature and to allow 
the development of sand wavelike bedforms visible in some high- 
resolution images of the deposit. A largely uncemented state is also 
needed to explain the radar signature, requiring relatively rapid 
deposition and little to no subsequent cementation or diagenesis. 
This requirement probably can be met because ocean transgres- 
sions on Mars were likely short-lived and separated by long periods 
with temperatures below freezing, thus preventing dissolution and 
cementation through rain or groundwater migration within the de- 
posit. Finally, carbonate precipitation would have taken place fairly 
rapidly when liquid water was present due to the planet’s high 
atmospheric CO, content. Surface science that can address the 
chemicaUmineralogica1 composition and physical properties of this 
material would be very important to understanding a relatively 
recent (Amazonian) volcanic or paleoclimatic process that resulted 
in a 2,700,000-kmz deposit along the martian equator. Based on 
assumptions about the average thickness of this deposit, this area 
corresponds to a total volume of material on the order of 27,000- 
2,700,000 km3. The proposed Pathfinder landing site lies on a 
relatively smooth, “unmodified” portion of the MFF, more than 
100 km away from its northern and western edges, which exhibit 
evidence of eolian etching in the form of closely spaced yardangs. 
There are no large craters or steep slopes within a few hundred 
kilometers of the landing site. 
References: [ I ]  Forsythe R. D. and Zimbelman J. R. (1990) 
LPS XXI,  383-384. [2] Scott D. H. and Tanaka K. L. (1 982) JGR, 
87, 1179-1 190. [3] Lee S. W. et al. (1982)JGR, 87,10025-10041. 
[4] Thomas P. (1982) JGR, 87,9999-10008. [SI Schultz P. H. and 
Lutz-Garihan A. B. (1988) Icarus, 73, 91-141. (61 Parker T. J. 
(1991) LPS XXII,  1029-1030. [7] Mouginis-Mark P. (1993) LPS 
XXIV, 1021-1022. [8] Halley R. B. et al. (1983) Bank Margin 
Environment, 464506,  AAPG. [9] Bathurst R. G. C. ( I  97 1) Car- 
bonate Sediments and Their Diagenesis, Chapter 7, Elsevier. 
5)# J /  , N95- 161 97 
\ ‘  
SCIENTIFIC RATIONALE FOR SELECTING NORTHWEST 
TUDE) AS A POTENTIAL MARS PATHFINDER LANDING 
SITE. T. J. Parker’ and J. W. Rice2. Jet Propulsion Laboratory, 
ICalifornia Institute of Technology, Pasadena CA 91 109, USA, 
2Department of Geography, Arizona State University, Tempe AZ 
85282, USA. 
ISIDIS PLANITIA (14’-17’N LATITUDE, 278’-281’ LONGI- 
The northwest Isidis Basin offers a unique opportunity to land 
near a fretted terrain lowlandupland boundary that meets both the 
latitudinal and elevation requirements imposed on the spacecraft. 
The landing site lies east of erosional scarps and among remnant 
massif inselbergs of the Syrtis Major volcanic plains. The plains 
surface throughout Isidis exhibits abundant, low-relief mounds that 
are the local expression of the “thumbprint terrain” that is common 
within a few hundred kilometers of the lowlandupland boundary. 
These typically occur in arcuate chains, often with a summit pit or 
trough. They have been variously interpreted as volcanic cinder 
cones or psuedocraters [I] ,  pingos [2], oreolian deposits that formed 
at the edge of a sublimating ice sheet [3]. We have used photo- 
clinometry to measure similar mounds in Cydonia, using photocli- 
nometry, at no more than a few tens of meters high, implying very 
gentle slopes. Cinder cones should exhibit slopes determined by the 
ballistic emplacement of unconsolidated material, and so they com- 
monly approach the angle of repose. 
Pingos are typically conical-shaped ice cored hills up to 100 m 
high and 600 m in diameter [4]. Many pingos often exhibit dilation 
cracks radiating from the apex of the hill. These fractures are created 
as a result of the growth of the ice core. This process exposes the ice 
core and allows it to thaw out, thereby producing acollapsed summit 
area. Pingos are usually located in lowland areas, especially lake 
beds and deltas. Lander and rover observations should be able to 
confirm whether these landforms are pingos or cinder cones based 
on the presence of dilation cracks or slopes approaching the angle 
of repose. The discovery of pingos would be of high importance to 
https://ntrs.nasa.gov/search.jsp?R=19950009782 2020-06-16T08:52:57+00:00Z
LPI Technical Report 94-04 35 
future missions to Mars, both robotic and "folked." The pingo ice 
core could contain relatively pure water ice within several meters of 
the surface. 
The massif inselbergs are not as numerous nor as massive as 
those in fretted tenains to the northwest, so local slopes arc not 
expected to be steep. Neither feature should pose a serious threat to 
the lander. Landing on or adjacent to one of these features would 
enhance the science return and would help to pinpoint the landing 
site in Viking and subsequent orbiter images by offering views of 
landmarks beyond the local horizon. 
[I] Lucchaa B. K. (1981) fcarus, 45, 264-303. 
[2] Frey H. and Jarosewich M. (1982) JGR, 87, 9867-9879. 
[3] Grimffi P. and Schultz P. H. (1989) Icarus, 77. [4] Washburn 
A. L. (1980) Gedcryology, Wiley, 406 pp. 
References: 
J- N95- 161 98 
/ 
CERBERUS PLAINS: A MOST EXCELLENT PATHFINDER 
1 LANDING SITE. J. B. Plescia, Jet Propulsion Laboratory, 
California Institute of Technology, Pasadena CA 91 109, USA. , ' 
Introduction: The Cerberus Plains in southeastern Elysium 
and western Amazonis cover > I 8  km2, extending an east-west 
distance of -3000 km and a north-south distance of up to 700 km 
near 195'. Crater numbers are 89 f 15 craters > I  km/106 km2, 
similar to values obtained by [2,3], indicating a stratigraphic age of 
Upper Amazonian and an absolute age of 200-500 Ma [I]. The 
material forming the surface is referred to as the Cerberus Forma- 
tion. The unit's origin is controversial; two ideas have been postu- 
lated, fluvial [4,1] and volcanic [5]. Regardless of which interpre- 
tation is correct, the Cerberus Plains is an important candidate for 
a Pathfinder landing site because it represents the youngest major 
geologic event (be it fluvial or volcanic) on Mars. 
Chlogy: The unit exhibits lobate albedo patterns and embay- 
ment relations with older terrane. These patterns suggest flow 
eastward across Cerberus. then northeastward through the knobby 
terrane into Amazonis (exploiting a series of older channels carved 
into knobby tenane and ridged plains). Albedo patterns in the east 
are regionally organized into bands up to 40 km wide; in the west, 
albedo patterns are complex and intricate with digitate boundaries. 
Small-scale surface texture is variable. Near 19ON. 174OW, where 
the unit fills a channel, the floor appears smooth, whereas the sur- 
rounding terrane has significant texture. The southern margin ex- 
hibits pressure ridges, flow fronts, and flowage around obstacles. 
The morphology of the Cerberus Plains is interpreted to indicate 
that it is an example of flood-basalt volcanism (e.g.. Deccan Traps, 
Columbia Plateau); the morphology of the western part indicates 
plains-style volcanism (e.g., Snake River Plains). Terrestrial flood 
basalt provinces [6,7] are characterized by flows 5-45 m thick 
extending over large areas having little relief. Eruption rates are 
very high with fissure vents tens to hundreds of kilometers long in 
zones several kilometers wide. Six low shields have been identified 
in the western plains. Some of the Cerberus shields are elongate, 
having elliptical vents; others are more symmetric. 
Pathfinder Mission Implications: The Cerberus Formation 
occurs between longitudes 165O and 220' and latitudes 5"s and 
30°N, although the material does not completely cover this area. The 
largest expanse occurs at 18Oo-2lO0W and 5's-10"N. Thus, the 
area of exposure is within the Pathfinder constraints (0°-30"N). 
Elevations [8] are at altitudes <-I km; a northeast-trending band 
from SON, 197OW toward IO0N, 18OOW has elevations e-2 km. 
These altitudes are within the Pathfinder range (4 km). A 100- 
km x 200-km ellipse along a N74'E trend is easily found within the 
unit; a target for the center of the landing ellipse is 6ON, 183'W. a 
location enswing landing within in the unit. The Cerberus region 
has low thermal inertia [9] (<4 x 10-3 cal cm-2 s-1'2 K-1). interpreted 
to indicate a low rock fraction exposed at the surface [lo], c1W. 
This suggests the area would be relatively safe for landing, but still 
offers the potential for finding exposed rock. 
Possible Scientific Implications: The first question to be 
resolved is whether the Cerberus Formation is of volcanic or fluvial 
origin. This alternative is testable with both imaging and elemental 
data. A volcanic flood basalt terrain should show a level, possibly 
slightly rolling surface; flow fronts and pressure ridges may be 
present. Rock analysis, both spectral and elemental, should show a 
relatively uniform composition. A fluvial environment should show 
channels and a scoured surface, and evidence of erosion should be 
abundant at all scales. Since debris on the surface would be from 
many sources, significant heterogeneity would be expected in the 
spectral and elemental analysis of the rocks. 
It can be postulated that the Cerberus Plains are the source for 
some of the SNC meteorites, specifically shergoaites, on the basis 
of age and volcanic style. Shergotty, Zagami, ALHA 77005, and 
EETA 7900 1 have ages of 160-1 80 Ma [ 1 I ,  121. Only the Cerberus 
Formation is of sufficient size and age to be a statistically significant 
source region. Major-element chemistry for the shergottites is Si02 
at 43-518, FeO at 18-208, AI20, at 3-946. MgO at 9-285, and 
CaO at 3-1 1%. The apx unit will provide key elemental data at the 
percent level. Shergottites are dominated by pigeonite (-2640%), 
augite (1 137%). and plagioclase-maskelynite (1 0-29%). The pres- 
ence of these minerals may be detectable by the filters in the imaging 
system, depending on the choice of band passes. These two instru- 
ments should provide sufficient data to determine whether the 
Cerberus Formation is the unit from which the shergottites were 
derived. 
The interpretation that Cerberus Plains results from flood volca- 
nism late in martian history carries implications for martian thermal 
history. Although central vent volcanism has been recognized as 
occurring late, flood volcanism has not. Flood volcanism in the 
period <700 Ma indicates that, at least in the Elysium region, 
sufficient heat remained to generate large volumes of low viscosity 
lavas. 
[ I ]  Tanaka K. L. (1986) Proc. LPSC 17rh, in 
JGR, 91, E139-EI58. [2] Carr M. and Clow G. (1981) Icarus, 48, 
91-1 17. [3] Scott D. H. and Tanaka K. L. (1986) USGS Misc. Inv. 
Map I-1802A. [4] Tanaka K. L. and Scott D. H. (1986) LPS XVII, 
865-866. [5] Plescia J. (1990) Icarus, 88,465-490. [6] Greeley R. 
(1976) Proc. LSC 7rh, 2747-2759. [7] Greeley R. (1982) JGR, 87. 
2705-2712. [8] USGS (1991) USGS Misc.lnv. Map 1-2160. 
[9] Christensen P. R. (1986)JGR, 91,3533-3545. [lo] Christensen 
P. R. (1986) Icarus, 68, 217-238. [I  I ]  McSween H. (1985) Rev. 
Geophys., 23, 391-416. [I21 Jones J. (1986) GCA, 38,517-531. 
References: 


Scientific rationale for selecting northwest Isidis Planitia (14 deg - 17 deg N latitude, 278 deg - 281 deg longitude) as a potential Mars Pathfinder landing site

Scientific rationale for selecting northwest Isidis Planitia (14 deg - 17 deg N latitude, 278 deg - 281 deg longitude) as a potential Mars Pathfinder landing site

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