CERRO NEGRO VOLCANO, NICARAGUA: AN ANALOG FOR GEOCHEMICAL PROCESSES ON EARLY MARS AND ASSESSMENT OF THEIR POTENTIAL FOR LIFE

Sulfate-rich bedrock has been discovered in many locations on Mars and has been studied by both orbiting spacecraft and landers. In most cases, these minerals were probably produced by acid-sulfate weathering of igneous rocks, which may have been a widespread process for the first billion years of Mars' history. The origin of life on Earth may have occurred in iron-sulfur hydrothermal settings and it is conceivable that Mars had a similar history since there was abundant heat and water in the first billion years of the planet's existence. Acid-sulfate weathering often dominates the geochemistry of subaereal volcanic hydrothermal settings on Earth and assessing the biological potential of such environments is paramount in assessing the potential habitability of early Mars.

A wonderful terrestrial analog for acid-sulfate weathering of Mars-like basalts exists at Cerro Negro, Nicaragua. Here, a similar basaltic chemistry to that of Mars is being rapidly chemically altered in a solfatara-like setting. Typical alteration products include abundant sulfates, iron hydroxides, minerals in the alunite/jarosite group, and contain up to 30 wt% S. These results are consistent with inferences and measurements from the Opportunity Rover and orbiting spectrometer data. Interestingly, several samples contain up to 80 wt% Si in the form of opaline silica. Similar compositions were found in bedrock near Home Plate in Gusev Crater by the Spirit Rover and the site is thought to have formed in a hot volcanic environment.

The microbial community near the fumarolic activity at Cerro Negro is being scrutinized to assess the habitability of these types of environments thought to be present on early Mars. Characterized by high temperatures, low pH, and high sulfur contents, these gas-dominated systems are the extreme of extreme environments and represent a unique and little explored microbial habitat. Roughly two orders of magnitude less biomass exists relative to samples from hot springs environments. Characterization of the phylogenetic diversity and metabolic functions is currently underway to understand the types of organisms and their survival strategies. The results suggest that there were formidable challenges for the potential development and sustainment of life on Mars.