ESA’s Mars Express has observed the southern part of a 440-km wide crater, informally named Ladon basin.
New images reveal a variety of features, most notably the double interconnected impact craters Sigli and Shambe, the basins of which are criss-crossed by extensive fracturing.
This region is of great interest to Mars researchers since it shows significant signs of ancient lakes and rivers.
Large-scale overview maps show clear evidence that vast volumes of water once flowed from the southern highlands. This water carved Ladon Valles, eventually flowing into Ladon basin, an ancient large impact region.
Elliptical craters are formed when asteroids or comets strike the surface of the planet at a shallow angle.
Scientists have suggested that a fluidised ejecta pattern indicates the presence of subsurface ice which melted during the impact. Subsequent impacts have created a number of smaller craters in the ejecta blanket.
The interconnected craters Sigli and Shambe are thought to have formed later when an incoming projectile split into two pieces just before impact. The joined craters were then partly filled with sediments at some later epoch.
Deep fractures can be seen within the craters whilst in the central and right part of the image, smaller craters and more subtle curved fractures appear. These fractures on the basin floor extend beyond the image borders and form concentric patterns.
The fractures are believed to have evolved by compaction of the huge sediment loads deposited within the impact basin.