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Spirit’s Exploration of the Columbia Hills: Ultimate Groundtruth for the 2020 Mars Rover

Wednesday, July 24, 2013
James
Rice

The Mars Exploration Rover Spirit explored the diverse and complex geology of the Columbia Hills region of Gusev Crater for over five and a half years. This presentation will report on the geomorphology and stratigraphy of several key features in the Columbia Hills and how they relate to the geologic evolution of this region of Mars.

The Columbia Hills form a rugged ridge complex comprised of 7 peaks spanning some 3.5 km in length and reaching a maximum height of 130 m above the basaltic plains of Spirit’s landing site. Several hypothesis have been put forth to explain the origin of the Columbia Hills: Old eroded partially buried impact crater rim(s), central peak, residual intracrater fill material, volcanic construct, or wrinkle ridge.

Home Plate is a roughly circular shaped plateau structure 2 to 4 m high and 90 m diameter, is located on the floor of the Inner Basin of the Columbia Hills. The Inner Basin is an amphitheater shaped lowland which opens westward toward the basaltic plains. Spirit reached Home Plate on sol 744 and found this feature to be composed of inward dipping layered rock capped with scoriaceous basaltic rocks.

Home Plate is composed of two major rock units. The lower unit is a massive, fairly coarse, poorly sorted ribbed rock with wavy undulations, containing subrounded to rounded coarse granules up to several mm in size and rounded voids. The upper unit is a finer grained, moderately sorted, finely laminated, matrix supported cross bedded clastic rock. All of the above features suggest that Home Plate may have been created by hydro- volcanic explosions forming a tuff ring or maar that was subsequently eroded.

The proposed 2020 Mars Rover is the next logical step for addressing the goals of astrobiology and geology communities. Spirit’s mission doubles as a trailblazer for the Mars 2020 Rover by providing the ultimate in ground truth. Spirit has already located numerous geologically significant outcrops (carbonates, opaline silica, sulfates) and sampling sites that the 2020 Rover could take advantage of by acquiring samples for the eventual return to Earth. Spirit’s field geology investigations in the Columbia Hills has revealed a very rich and diverse landscape which I propose would be a very fitting landing site for the Mars 2020 Rover. The Columbia Hills would provide the following types of key samples:

1. Opaline silica deposits (up to 91 weight percent SiO2)formed in a hydrothermal environment.
2. Carbonates (16 to 34 wt %) indicating extensive aqueous activity under near-neutral pH conditions which would be conducive to habitable environments on early Mars. Additionally, silica and carbonate precipitation are well known to promote biosignature preservation.

The Mars 2020 Rover would also be able to investigate features that Spirit wasn’t able to explore. For example, von Braun Butte, the Promised Land, and Goddard Crater which may be a volcanic source vent. An extra incentive for revisiting this site is that Spirit can be located and inspected (i.e., Apollo 12 and Surveyor III). By this time Spirit would have been exposed to the Martian environment for over 15 years. Thereby, making for an excellent long duration exposure experiment providing long-term data on the Martian environment, including weathering, micrometeorites, and its effects on materials degradation and other systems (including power, propulsion, and optics). This data will aid in the design of surface systems, equipment and structures for the future robotic and manned exploration of the planet. 

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