Age and geology
The highland regions of the southern hemisphere of Mars are covered with impact craters. The craters are much more numerous than in the northern hemisphere, which proves that these regions are among the oldest on the planet. One of these regions is called Noachis Terra and gave its name to the Noachian Period, an epoch that lasted from approximately 4.1 to 3.7 billion years ago and was marked by a strong bombardment by meteorites and asteroids. In this early phase of the planet, large regions were topographically shaped, hence the name Noah, after the ark builder in the Old Testament. The images show three superimposed impact craters. The largest of them measures 45 kilometres across, the middle one approximately 34 and the smallest 28. One scenario for the formation of the craters could be that a meteoroid broke into at least three pieces before all three bodies hit the surface of Mars in succession.
However, it could also be a coincidence that three impactors hit Mars independently at almost the same location over a somewhat longer time interval. Due to the fact that there are still residues of its ejecta blanket around the smallest crater, it is obvious that this smaller crater was formed after the two larger ones. Their ejecta blankets have long since been eroded and blurred. At the northern rim of the crater triplet (top right in the color image, color-coded terrain model, anaglyph) another small, circular structure is visible, possibly representing a fourth, now filled impact crater.