Mare Tyrrhenum

Mare Tyrrhenum, which is located at 230S and 2310W, is similar to the landing site of Eridania Plains, because of its location between ancient cratered terrain and high ridged plains formed from lava floods of more recent occurrence. In the ancient cratered terrain, there are several valley systems which are assumed to have been formed before the plains. The evidence of the earlier formation of these geologic structures in comparison to the plains is given as in all the other future sites by the analysis of the orbiter images of the Viking missions.

These images show that the lava floods composing the plains also fill a closed depression or basin into which the valleys drained at some point in time. The covering of this basin by lava hints at the possibility of fluvial sediments being buried under it. In the case the lava ad not covered this area, the water lain sediments would have probably almost completely disappeared from the soil as a result of erosion and climatic activity.

The analysis of the newer plains will in the future be aided by the presence of relatively new impact craters which have forced soil from different depths close to or to the surface of the area. These craters, which are for the most part 6 km in diameter, were formed after the plains and have excavated deep into the soil of this area.

The Viking images suggest that the surrounding valley networks were formed in a period between the intense meteorite bombardment of the surface and a later period of fewer and smaller implacts. These structures, which account for most of the basin walls, terminate abruptly mear the basin. This suggests that during the time of liquid water on the surface, sediments might have built up at the ridged walls surrounding the area. These sediments, if they exist in the area, could have been caused by either water flow or water ponding.

Mare Tyrrhenum is a landing site of interest for the biological analyzes of the planet, because of its probable high content of sedimentary rock, and the ability of this type of rock to preserve both fossil or organic samples.