Site 06 : Sinus Sabeus Northeast (White Rock)

MC-20 NE

Viking Orbiter Images : 347S11, resolution is 815 m/pxl ; 623A70, resolution is 80 m/pxl ; 575B76, resolution is 30 m/pxl ; 826A39 through 44, resolution is 50 m/pxl.

Geologic Setting :

This site, located within a plains region of intermediate age (of the Hesperian period) is a very unusual bright-appearing feature first observed by Mariner 9 that lies within an 80 km crater in the Sinus Sabeus quadrangle.

Scientific Rationale :

The bright feature could be salt deposits formed at the bottom of a lake and, if so, may have preserved organics or, even, fossils.

Exobiology Significance :

Numerous channels resembling terrestrial dendritic drainage systems surround the crater basin. The crater floor itself is rather patchy in appearance. The brightest feature in the region is an irregular mound referred to from the time of its first discovery in 1972 as "White-Rock". It is located in the southwestern quarter of the targeted crater. White-Rock is about 18 km wide, 100 m high, and contains multiple irregular, presumably wind eroded fractures, that somewhat resemble terrestrial sand dunes known as "yardangs". White-Rock is partially encircled by a dark band of unknown origin. Bright streaks with an albedo similar to White Rock are visible in high resolution images to the southeast of the crater and are thought to be wind-blown deposts.

White rock has been interpreted to be similar to features called playas found in terrestrial deserts -- the remnants of lakes that have dried up, leaving beind salt deposits. Such salt deposits are precipitated from chemical solution and, as such, differ from deposits precipitated by simple sedimentation of sand and debris. This interpretation suggests a local hydrological system which operated over a prolonged period, concentrating soluble salts and subsequently precipitating them when the solution became saturated. Such mineral salts offer potential for preserving organic material and microbial fossils.

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