Site 05 Hebes Chasma

MC-18 NW

Viking Orbiter Images : 915A04, 06, resolution is 60 m/pxl ; 917A03, 06, resolution is 60 m/pxl ; 919A03-06, resolution is 65 m/pxl.

Geologic Setting :

The site is located in Hebes Chasma, an elongated, closed canyon that is part of the great Valles Marineris system. The landing target is located in an area where layered rocks have been exposed, apparently sedimentary rock formations

Within this martian canyon there is a raised plateau (or "mesa") which dominates the landscape of this huge depression and also is made up of layered rock formations. The canyon floor is covered by deposits of the youngest period (Amazonian) which presumably lie on top of the older (Hesperian) bedrock that forms the valley bottom.

Scientific Rationale :

The origin of the giant Valles Marineris system is thought to include episodes of massive crustal faulting and erosion by wind, water and landslide. Most of the vast quantities of water that flowed through the system evidently drained out to lower ground at the eastern end. However, for some of the closed canyons, water would have been trapped to form vast lakes -- environments that led to sedimentation and that may have favored complex chemical evolution. Thus, the layered deposits exposed in the walls of the Hebes mesa may well include water-laid sediments with preserved organics and, even, fossils. These sediments will be the target of the landed spacecraft.

Exobiology Significance :

Spur and gully landforms characterize the sides of the mesa and, by Earth-based analogy, suggest erosion by water, perhaps episodic. The steep slopes that form the base of the mesa are interpreted to be rock falls and debris avalanches from the rim and walls of this plateau. Landslides cover the basin floor in places.

The proposed landing site is on the basin floor, at the edge of a debris slope that rises steeply upward, towards the mesa rim. This will provide the rover with access to rocks that have broken off from the layered formations in the mesa walls and rolled down to the canyon floor.

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