  The Special Collection of papers in this issue of Astrobiology provide an
overview of the characteristics and potential for future exploration of the
Ojos del Salado volcano, located in the Andes Mountains in front of the Atacama
Desert in northern Chile. The main benefits of this site compared with others
are the combination of strong UV radiation, the presence of permafrost, and
geothermal activity within a dry terrain. The interaction between limited snow
events and wind results in snow patches buried under a dry soil surface. This
leads to ephemeral water streams that only flow duringdaytime hours. On this
volcano, which has the highest located subsurface temperature monitoring
systems reported to date, seasonal melting of the permafrost is followed by
fast percolation events. This is due to the high porosity of these soils. The
results are landforms that shaped by the strong winds. At this site, both
thermal springs and lakes (the latter arising from melting ice) provide
habitats for life; a 6480m high lake heated by volcanic activity shows both
warm and cold sediments that contain a number of different microbial species,
including psychrophiles. Where the permafrost melts, thawing ponds have formed
at 5900m that is dominated by populations of Bacteroidetes and Proteobacteria,
while in the pond sediments and the permafrost itself Acidobacteria,
Actinobacteria, Bacteroidetes, Patescibacteria, Proteobacteria, and
Verrucomicrobia are abundant. In turn, fumaroles show the presence of
acidophilic iron-oxidizers and iron-reducing species. In spite of the extreme
conditions reported at Ojos del Salado, this site is easily accessible.
