Abstract

The McMurdo Dry Valleys detailed in previous chapters represent one environment for life thought to have existed on Mars among many. This chapter illustrates other potential habitats and their significance: (1) high-altitude lakes subjected to rapid climate change in the Andes provide analogy to the Noachian/Hesperian transition on Mars; (2) Río Tinto, Spain, where conditions are reminiscent of Meridiani Planum, unravels an underground anaerobic chemoautotroph biosphere that could resemble a modern refuge for life on Mars; (3) the High Arctic hosts gullies analogous to those observed on Mars, whose fresh deposits could provide access to traces of past and/or present underground oases; it is also in this polar environment that the Haughton-Mars Project helps answer long-standing questions, revisiting classical assumptions, and sometimes reshaping our thinking on many issues in planetary science and astrobiology, in particular in relation to Mars; (4) the search for microbial life in the arid soils of the Atacama desert and its robotic detection characterize what role aridity plays in the distribution of life and how to search for evidence of rare and scattered biosignatures.

Introduction

Because of its geology and climate evolution, Mars is likely to have developed a diversity of potential habitats for life over time. The main ingredients for habitability (i.e., water, energy, and nutrients) were present early, as demonstrated by the Spirit and Opportunity rovers at Gusev crater and Meridiani Planum (Knoll et al., 2005; Des Marais et al.,2005, 2008).

Introduction

A series of astrobiological high-altitude expeditions to the South American Andean Mountains were initiated in 2002 to explore the highest perennial lakes on Earth, including several volcanic crater lakes at or above 6000 m in elevation. During the next five years, they will provide the first integrated long-term astrobiological characterization and monitoring of lacustrine environments and their biology at such an altitude. These extreme lakes are natural laboratories that provide the field data, currently missing above 4000 m, to complete our understanding of terrestrial lakes and biota. Research is being performed on the effects of UV in low-altitude lakes and models of UV flux over time have been developed (Cockell, 2000). The lakes showing a high content of dissolved organic material (DOM) shield organisms from UV effects (McKenzie et al., 1999; Rae et al., 2000). DOM acts as a natural sunscreen by influencing water transparency, and therefore is a determinant of photic zone depth (Reche et al., 2000). In sparsely vegetated alpine areas, lakes tend to be clearer and offer less protection from UV to organisms living in the water. Transparent water, combined with high UV irradiance may maximize the penetration and effect of UV radiation as shown for organisms in alpine lakes (e.g., Vincent et al., 1984; Vinebrook and Leavitt, 1996). Shallow-water benthic communities in these lakes are particularly sensitive to UV radiation. Periphyton, which defines communities of microorganisms in bodies of water, can live on various susbtrates.