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Date Entered: 6 September 1988
The Memnonia site is in a valley between the northern lowland plains and southern highlands. The landing area is on ridged plains lava flows, a globally extensive rock unit of intermediate (Hesperian) age. The ridged plains are overlain to the north by very young (Amazonian) rocks postulated to be ash-flow tuffs (Scott and Tanaka, 1982, 1986) or paleopolar deposits (Schultz and Lutz, 1988). On the south side of the valley the ridged plains embay ancient (Noachian) cratered highlands. A small young channel of unknown origin is close (6 km) to the landing site. Viking images (~50 m/pxl) indicate the area is relatively smooth and free of obstacles.
Scientific Rationale
In situ rock outcrops of young (Amazonian), intermediate (Hesperian), and ancient (Noachian) ages occur within about 0-15 km from the landing site. Young stream channel deposits and layered material in the channel gorge could also be sampled. Ridged plains lava flows of Hesperian age are considered to be the most important rock units for determining the absolute age of the bend in the martian cratering rate curve where the rapidly decaying early flux changes to a nearly constant rate (Neukum, 1987). Together with Amazonian and Noachian rock samples they would provide data on the composition and radiometric ages for major rock units on Mars.
Objectives
Primary sample locations (fig. 1) are numbered in table 1; targets of opportunity that might be sampled enroute are indicated by letters. The landing and ascent sites are assumed to be the same or close together.
Summary of objectives:
a) Rocks of intermediate age (Hesperian) at landing site (success excellent);
b) possible pyroclastic rocks of very young age (Amazonian) near (~15 km) landing site (success very good);
c) ancient rocks (Noachian) near (5-15 km) landing site (success very good);
d) fluvial materials and young outflow channel near (6 km) landing site (success excellent).
Potential Problems
Stream channel and floodplain deposits including large rocks may be more extensive than presently apparent--need much higher resolution images than 40 m/pxl.
Trafficability
Appears good at image resolution.
Estimated Traverse Distance
1) 35 km
2) 40 km
Total 75 km
REFERENCES
Neukum, G. 1987. Absolute ages from crater statistics: Using radiometric ages of martian samples for determining the martian cratering chronology (abs.), in Workshop on Mars Sample Return Science, LPI Tech. Rept. 88-07, pp. 128-129.
Schultz, P.H., and A.B. Lutz, 1988. Polar wandering on Mars: Icarus, 73, 91-141.
Scott, D.H., and K.L. Tanaka 1982. Ignimbrites of the Amazonis Planitia region of Mars: J. Geophys. Res., 87, no. B2, 1179-1190.
Scott, D.H., and K.L. Tanaka 1986. Geologic map of the western equatorial region of Mars. U.S. Geol. Survey Miscellaneous Investigation Series Map I-1802A.
Table 1. Materials to be sampled on proposed landing site traverses at primary sample stations (numbers) and secondary targets of opportunity (letters). Landing site (LS) and traverses shown in the site figure.
Est. min. Station/ dis. from Target LS (km) Sample description and geologic significance
1 (LS) 0 Basalt flows of intermediate age (unit Hr); widespread
occurrences; globally correlative geologically and by crater
counts.
A 6 Channel material (unit Ach) in bar or island remnant; TV
scan for layering, sorting, size distribution.
B 13 Knobby material (unit Nk).
2 16 Member 2 (unit Am2) of Medusae Fossae Formation
(young ash flow?); TV scan to determine nature of contact
with adjacent basalt flows (unit Hr) and
knobby material (unit Nk).
3 21 Channel gorge cutting possible layered basalt flows (unit
Hr) and older rocks.
C 26 Samples and TV scan along channel from station 3 to C to
observe possible layering of basalt flows in channel
wall.
4 32 Ejecta and rim material around 500-m-diameter crater in ridged plains unit.
1 (LS) 35 Completion of first traverse.
D 5 Ejecta and rim material around 600-m-diameter crater in
ridged plains unit.
5 14 Rim of Noachian (c1) crater.
E 16 Ridged plains/c1 contact from station 5 to E.
6 23 Wrinkle ridge in ridged plains unit; TV observation of
ridge structure.
7 25 Ejecta and rim material from young crater (1,500 m in
diameter) in ridged plains unit.
8 29 Fresh crater (300 m in diameter) superposed on channel
material and on basalt of ridged plains unit.
F 31 Channel material.
1 (LS) 40 Completion of second traverse.
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75 km Total distance of two traverses.
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