Site 01 : Eridania Northwest

Site name : Eridania Northwest Type of Site : Rover Sample Return

Latitude : 36 ∞ S
Longitude : 228 ∞ W
Elevation : +3.0 to + 4.0 km

Corresponding map in The Atlas of Mars : MC- 29 NW

Viking Orbiter Images : 420S16 through 420s21. Resolution is 90 m/pxl

Geologic Setting

The site lies at the contact between ancient cratered terrain and ridged plains materials that are probably less ancient flood lavas that we describe as of intermediate age. The valleys apparently were formed before the plains materials. The relationships are sufficiently unclear that we cannot be sure whether the fluvial sediments underlie the plains materials. Fresh (and therefore relatively young) craters of up to about 10 km in diameter excavate into the plains materials. In addition, there are a few ancient buried craters that can be recognized by their rims which protrude upward through plains materials.

This particular site will provide important information on both ancient cratered terrain and more recent volcanic materials. Because of the fluvial activity the site is also highly interesting to exobiologists.

Exobiology Significance :

The plains occupy a depression or basin and, given the surrounding drainage patterns, there may well once have been an ancient lake here. Complex tributaries and meanders cut into into the upper reaches of some of the more prominent channels suggest that water may have been active for a long period. The floor of any such ancient lake is now covered by volcanic materials -- which creates an obvious sampling problem which we will address later.

If lake sediments are present in the basin they may provide a record of long term water processes, and possibly, a fossil record. Deposits in the central region of an ancient lake are expected to include fine-grained sediments and perhaps salts formed by evaporation.

On Earth such sediments and evaporites often favor the preservation of organic matter.

Given that the younger plains units covering the basin floor are probably volcanic in origin and therefore not of immediate interest to exobiologists, the proposed landing target (37 deg.S/230 deg.W) is located on the ejecta blanket of a 40 km diameter crater. Crater ejecta, thrown up from depth, offer the best opportunity to sample the subsurface deposits which underlie the ridged plain unit (impacting bodies are nature's own excavator and are likely to be of key importance for sampling some ancient materials).

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