Permafrost Astrobiology: Field Expedition to Terrestrial Analogues of Martian Habitats and Inhabitants
When: December 1, 2010 11AM PST
The terrestrial cryosphere, where life is confined over geological time, is the only widespread and rich Earth’s depository of viable ancient organisms. The cells, their DNA, metabolic by-products and bio-signatures found in the Earth’s cryosphere provide analogues that could be used in the search for possible ecosystems and inhabitants on planets and extraterrestrial bodies of cryogenic type. If life ever existed here during the early stages of development, then its traces may consist of primitive cell forms. Similar to Earth, they might have been preserved and could be found at depths within the ice or permafrost. Most intriguing are the traces of past or existing life on Mars; these are of interest due to the upcoming missions.
Microorganisms isolated from the ice cores from both Earth’s hemispheres have been interpreted to be most representative analogues of icy inhabitants of Martian ice caps. The main part of the planet is without obvious surface ice. In this part, a range of potential cryogenic ecosystems is represented by permafrost – the most inhabited and ancient environment of the terrestrial cryosphere, which maintains life incomparably longer than any other known habitats. The age of the isolates corresponds to the longevity of frozen state of the embedding strata and the oldest known date back to late Pliocene. Permafrost on Earth and Mars vary in age, from a few million years found on Earth to a few billion years on Mars. Such a difference in time scale would have a significant impact on the possibility of preserving life on Mars. This is why the longevity of life forms preserved within terrestrial permafrost can only be considered an approximate model for Mars.
I will focus on one of the terrestrial environments which is close to Mars in age – active volcanoes in permafrost areas. Here the age of volcanic deposits frozen after eruption is much younger than the age of surrounding permafrost. The same processes (the past eruptions of Martian volcanoes) periodically burned through the frozen strata by magma fluxes and formed the thermal and water oases. Simultaneously, products of eruptions (lava, rock debris, scoria, ash) rise from the depths to the surface and freeze. The age of these frozen volcanic deposits is also much younger than the age of surrounding permafrost. Images taken by the High Resolution Stereo Camera on board of ESA Mars Express discovered young volcanoes 2-15 Myr old on Mars. In other words, the age of the youngest Martian volcanoes date back to the age of volcanoes on Earth.
Culture- and culture-independent methods show the presence of viable thermo- and hyperthermophilic bacteria and their genes within piroclastic frozen material. These bacteria were never found in permafrost outside the areas of active volcanisms. The presence of thermophilic community in frozen ash and scoria raise the question about the origin of these microorganisms and their life style in such environment. High-temperature ecological niches are known as inhabited geothermal oases settled by thermophilic bacteria and archeae. There is only one way for thermophiles to get into frozen pyroclastic material that is through a deposition during eruption. In other words, the catastrophic geological events might transport thermophiles from the depths to the surface and these thermophiles might survive at subzero temperatures.
Such terrestrial microbial community might serve as a model for Mars with some of volcanoes date back to the age close to that one on Earth. It is reasonable to expect to find such viable thermophilic forms within Martian near-surface permafrost near young volcanoes. To explore these hypotheses we have to characterize different volcanic microbial communities on Earth within volcanic permafrost. One of such areas of active volcanism is Klyuchevskaya Volcano Group (55°'N, 160°E) on Kamchatka Peninsula in Russian Far-East, where mountainous permafrost predominates from the elevations ~1000 m asl and up.