Site 03: Mare Tyrrhenum

MC-22 SE

Viking Orbiter Images : 629A10, 629A12, 629A27, resolution is 250 m/pxl ; 423S01 through 423S03, resolution is 145 m/pxl.

Geologic Setting :

Like the site in Eridania this site lies at the contact between ancient cratered terrain and ridged plains materials that are apparently flood lavas of intermediate age. These lavas lap up against the higher cratered terrain at the contact. Many well-developed ancient valley systems are present in the cratered terrain and debouch at the contact. These valleys were evidently formed before the plains materials. The lavas seem to fill a closed depression (or "basin") into which valleys drain, so there is a possibility of waterlain sediments being present under the lavas. Relatively fresh craters up to about 6 km in diameter have excavated into the plains materials.

A mission on this site would seek to sample the ancient cratered terrain and also the less ancient (intermediate-aged) volcanics.

Exobiology Significance :

The valley networks appear to be been formed between the time that the intense bombardment that produced most of the larger craters (which took place as the final stage of planetary accretion from such asteroid-sized bodies) and a later period during which smaller impacts were still occurring regularly. The southern edge of the basin is defined by a large impact crater. The north wall of that crater has been partially destroyed by erosion -- perhaps by wind and possibly by water that may have filled up the basin to that level. There is some photo-geologic evidence of a shoreline that may have been modified by waves.

The abrupt termination of the valleys near the basin margin suggests that sediments caused by the flow and ponding of water may underlie the ridged plains material. The proposed landing site target is at 22.8 deg.S/ 230.6 deg.W on the ejecta blanket of a 12 km diameter crater located near the southern margin of the basin close to the termination of one of the major drainages. Here we would try to retrieve samples of the sedimentary deposits that evidently lie under the ridged plains terrain. As at other sites of interest to exobiologists, the sedimentary rocks are specially important because they may have been formed by processes involving liquid water and they could have preserved organics and even fossils.

Go to the next site

Back to the previous site