A huge crater and other features of a chaotic Martian
terrain can be seen in new images of the red planet.
The images, obtained by the High Resolution Stereo Camera
(HRSC) on the European Space Agency's Mars
Express orbiter, span the boundary between Kasei Valles and Sacra Fossae,
an area about the size of Manhattan.
The upper portion of the image swath shows the eastern
margin of Kasei
Valles and the western margin of the Lunae Planum plateau and the adjoining
Sacra Fossae. Kasei Valles is one of the largest outflow channels on Mars,
spanning about 1,900 miles (3,000 km), from the Chryse Planitia basin in the north
to Echus Chasma to the south.
Sacra Fossae is a fault system that extends for more than 600
miles (1,000 km). It is several hundred yards deep and separates Kasei Valles
to the south and west from Lunae Planum. It was named after Isola Sacra, an
island at the estuary of the river Tiber in Italy.
The images show an old 22 mile-diameter (35 km) impact
crater in the north. The crater's south-western rim is eroded strongly. The
erosion was caused mostly by flowing water. The source of the water was located
in Echus Chasma, which lies roughly 530 miles (850 km) to the southwest.
The crater floor and the northwestern part of the imaged
region are remarkably flat and have been formed by sediments and basaltic lava
flows originating from the Tharsis volcanic region.
The lower part of the image clearly shows the boundary
between the heavily cratered plain and the area with numerous fracture zones.
Most of the fractures along the boundary are parallel to the edge of the Lunae
Planum.
It is likely that the entire region experienced tectonic
stresses as well as 'subrosion' — a process where subsurface rocks are
dissolved and removed by water — causing overlying strata to collapse partially
and form chaotic terrain.
Several fracture zones are also visible in the western part.
Up to 6-mile (10-km) large areas that experienced 'subsidence' (gradual
compaction and sinking owing to the weight of the layers) are still intact.
advertisement
