Site 04 : Dao Vallis

MC-28 NE ; ASU-IPF 713

Viking Orbiter Images : 62S18-20, 32A529, 408S69 through 408S70, resolution is 108 m/pxl ; 410S02, 410S04 410S06, 410S09, resolution is 165 m/pxl ; 124A34, 124A37 through 124A40, resolution is 145 m/pxl ; 625A17 through 625A20, resolution is 235 m/pxl.

Geologic Setting :

The upper western branch of the outflow channel Dao Vallis lies between the flanks of the volcano Hadriaca Patera and the smooth-appearing (at available image resolution) Hesperian plains. The channel drops 5 km in elevation from its region of origin on the southern slope of Hadriaca Patera to its ending at the edge of the great impact basin Hellas Planitia where the terrain is a mixture of wind-blown, water carved and volcanic lava flows.

Scientific rationale :

At this complex site we have an opportunity to investigate an outflow channel, a major volcanic eruption and adjacent plains material adjoining it, even the lower reaches of Dao Vallis and the violent disruptions at the edge of the vast Hellas basin. From observations made over several years from orbit we know also that water frost, water vapor clouds, and dust storms are common both on the channel floor of the Dao Vallis channel and also in Hellas Planitia,

Objectives :

For this large and complex site we picture that mobility for science will need two vehicles equipped with cameras and other science instrument -- a surface rover and a hot air balloon (not unlike one built by the French Space Agency to fly on a Russian mission to Mars). The balloon is to be landed in the upper end of the western branch of Dao Vallis where it drops off a surface rover. When suitable morning northeast winds occur (as predicted) the balloon will take off for a daytime flight southwest over the floor of Dao Vallis to land again on the channel floor at nightfall. If the balloon vehicle successfully reaches the junction of the western and eastern branches of Dao Vallis at 37 deg S, 270 deg W, it should continue to fly southwest above the lower Dao Vallis channel, make observations during daylight hours, and follow Dao Vallis at least to its terminus in Hellas Planitia.

Estimated Traverse Distance :

300 to 1,000 km for Balloon Vehicle. Up to 300 km for the lander rover.

Exobiology Significance :

The simple physical form of the channel and its broad source area together suggest that Dao Vallis may have been formed by spring sapping. Furthermore, the closeness of Dao Vallis to a volcano with its underlying chambers of molten rock suggests the possibility of hydrothermal activity (like Yellowstone National Park).

The proposed landing site is located 33.2 deg S, 266.4 deg W near the head of Dao Vallis.

Formation of Dao Vallis clearly took place after the construction of the volcano, though we are not sure how long after. The simple form of the valley and its large size is interpreted to be consistent with a prolonged period of hydrologic activity rather than with a catastrophic release of water.

The proposed site is of great exobiology interest because of the possibility of sustained hydrothermal activity and associated mineralization. Using Earth-based analogies, thermal springs formations are regarded as excellent targets in the search for a fossil record on Mars because of the high biological productivity and the rapid way in which fossils are buried in the colorful minerals that form at thermal springs.

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