Rover observations in Gusev Crater: Evidence for a style of weathering unique to Mars?

Abstract

The Mars Exploration Rover “Spirit” provided us with a serendipitous opportunity to traverse a section of the ancient martian crust, acquiring a trove of imaging, geochemical, and mineralogical measurements along the way. This small window looking out on the Noachian period (>3.7 Ga), dubbed the Columbia Hills, pokes out from the younger, volcanically resurfaced floor of Gusev Crater. It was our first detailed look at early Mars, a time when liquid water appears to have played a much more prominent role in shaping and modifying the planet than later in its history. The abundance of rocks that appear to be snapshots from early in the history of Mars is a luxury compared to the rarity and inevitable metamorphic overprinting of Hadean and early Archean samples from Earth. However, few planetary surfaces of this age anywhere in the solar system escape the disruption caused by impacts. In this sense, it is difficult to identify the geologic context of any given sample or series of samples. Although what appears to be an outcrop of a draping volcaniclastic unit in the Columbia Hills may still be in place, it is also possible for it to have been highly …