Exotic Arctic Bacteria and Life on Europa
Until the 1970s, life, at least as the concept is generally understood, was believed to be entirely dependent on energy from the Sun. Plants on Earth's surface capture energy from sunlight to photosynthesize sugars from carbon dioxide and water, releasing oxygen in the process, and are then eaten by oxygen-respiring animals, passing their energy up the food chain. In 1977 chemosynthesis revolutionized the study of biology by revealing that life need not be sun-dependent; it only requires water and an energy gradient in order to exist. It opened up a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats. In a fjord in Canada scientists have found a landscape similar to one of Jupiter's icy moons: Europa. It consists of a frozen and sulfurous environment, where sulfur associated with Arctic bacteria offer clues for the upcoming missions in the search for traces of life on Europa.
It is not easy to find a place on Earth where ice and sulfur come together, supposedly like on Europa, Jupiter's moon. Nonetheless, this place has been located at Borup Fjord Pass in the Canadian High Arctic. Borup Fjord Pass is located on Ellesmere Island, a remote and all but inaccessible place in the Canadian High Arctic. Gleeson, as a graduate student, spent time at the pass in 2006, taking samples of the unique yellow stains left by sulfur-rich springs on the surface of the ice.
US researchers have now verified that the sulfur involved in the life cycle of Arctic microorganisms has some characteristics that could help to detect biological remains on Europa. Large space agencies like NASA and the European Space Agency are already in the process of preparing missions.
"We have discovered that elemental sulfur can contain morphological, mineralogical and organic biosignatures linked to bacterial activity. If they are found on Europa, this would suggest the possible presence of microorganisms," as explained to SINC by Damhnait Gleeson.
The glacial spring at Borup Fjord deposits sulfur, gypsum and calcite across glacial ice. Pure sulfur tends to react with oxygen to form gypsum, but it was shown that the sulfur was being replenished by microorganisms. Usefully, the sulfur produced by the microbes shows a complicated structure that is not apparent in control samples.
The biosignatures are associated with needle and rhomboid sulfur shapes in which mineralized remains of microorganisms and extracellular material appears. Thanks to electron microscopy and X-ray diffraction techniques, the formation of a rare type of sulfur has also been observed in association with organic components: the rosickyite. What is more is that small quantities (parts per million) of protein, fatty acids and other biomolecules have appeared in the sulfurous material.
"There is much evidence of bacterial activity," highlights Gleeson, who wonder if in the Europa's icy crust, or the ocean or lakes supposedly beneath it, there could be a similar microbial community that uses sulfur as their source of energy.
Most planetary scientists believe that a layer of liquid water exists beneath Europa's surface, and that heat energy from tidal flexing allows the subsurface ocean to remain liquid. Europa's surface temperature averages about −160 °C keeping Europa's icy crust as hard as granite. The first hints of a subsurface ocean came from theoretical considerations of tidal heating (a consequence of Europa's slightly eccentric orbit and orbital resonance with the other Galilean moons).
For further information see Arctic Ice.
Europa image via NASA.