Kicking off this blog with a rather long post based upon microbial extremophiles. In light of the recent discovery of water on Mars, I thought I’d write about the potential for life (microbial life) on other planets.
From the beginnings of modern science it has always been hypothesised that we are not alone in the universe. This idea has been the driving force behind years and years of science fiction writing, film and artwork. While many people may believe in extra-terrestrial life, it is not very well know that microbes may well hold the key. An extremophile is an organism that survives and thrives in a physically or chemically extreme environment that would be inhospitable to ‘normal’ organisms. Extremophiles are characterised by the environment they are found in, for instance a psychrophile is found in extreme cold, halophiles found in extremes of salt and xerophiles in extremely dry environments.
Space exploration has given us a huge base of knowledge of the solar system with detailed analysis of planets, including atmospheric makeup and surface composition. This has uncovered a number of environments which at first glance seem to be analogous to some of Earth’s extreme environments and could be hospitable to Earths extreme survivalists.
Lake Vostok is the largest of Antarctica’s subsurface lakes and is an example of an extreme cold environment. The body of water is below the ice shelf and has an average temperature of -3°C, it is thought that it remains liquid due to the pressure from the ice sheet above. The lake is in complete darkness (aphotic) but is rich in oxygen and nitrogen. Drill core samples were taken of the ice sheet above the lake and were found to contain a number of microorganisms of various ages. It is a particularly interesting environment to study due to the recent discovery of subsurface lakes on Europa, Jupiter’s sixth largest moon. It is made mostly of silicate rock with an iron core and has an oxygen atmosphere. The surface is mainly made up of ice, but the discovery of subsurface lakes on Europa has sparked hot debate as to whether the Sub glacial ecosystems found on earth are analogous to Europa. If they are similar, then it can be suggested that Europa would be perfectly capable of supporting microbial life.
Methylomirabilis oxyfera is an anaerobic denitrifying bacterium that has been found to utilise a new metabolic pathway to survive. It was found in methane-rich and anoxic soils under rivers and lakes. This bacterium produces its own oxygen (O). This oxygen then goes on to oxidise methane (CH4) into Carbon dioxide (CO2) and water (H2O). Titan is the largest moon of Saturn with a dense nitrogen-rich atmosphere (much like earths), the interesting thing about Titan is that it contains methane in the solid, liquid and gas states. With the abundance of methane it could be suggested that this moon could support life that utilises methane, in particular Methylomirabilis oxyfera that creates its own oxygen to metabolise methane.
Encaledus is another extra-terrestrial environment that has received great interest from astro-biologists, Encaleadus is a 500km wide moon of Saturn with an atmosphere consisting of mainly water vapour but also carbon dioxide, nitrogen and methane. The inner core is thought to contain silicates and iron. Since 2005 when Nasa’s Cassini probe discovered icy plumes jetting into the atmosphere there has been belief that there could be sub glacial lakes on Encaladus, recently the probe has discovered a sub-surface lake on the south pole. This environment (along with Europa) is particularly interesting because the sub-surface lake is thought to be in contact with the rocky core. Wachtershauser’s (1988) autocatalytic anabolism theory suggests that life started on minerals with an anabolic metabolism of synthetic, autocatalytic carbon fixation cycles. It could be argued that the sub-glacial lake in contact with a silicate and iron interior could generate the conditions needed for the first life to develop, and puts Encaledus and Europa on top of the list of places to search for microbial life.
Mars is the second smallest planet in our solar system and is nicknamed the ‘red planet’; this is due to the relative abundance of iron-oxide in its surface. It also has a thin atmosphere consisting mainly of Carbon dioxide with traces of oxygen and water. It is suggested that organisms could survive on mars using a mixture of water and hydrogen peroxide as an intracellular solvent. The lack of biotic findings has been explained by auto-oxidation at higher temperatures. Shuerger et al. (2013) while looking into the viability of earth bacteria ‘hitching’ a ride to mars, took 26 strains of 22 types of bacteria and subjected them to mars conditions and found that only Serratia liquefaciens grew at these conditions, this growth was surprising considering that S. liquefaciens is a generalist bacteria found in a range of environments and not considered extremophilic. From his findings it could be suggested that this organism could survive on mars, however previous Schuerger experiments (2003) suggest that the high UV radiation would sterilise 99.9% of the bacteria population within minutes on the surface of mars.
Aliens as we know them from the movies may not exist, but by looking at the variety and extremity of conditions that microorganisms can overcome compared to the analogous nature of extra-terrestrial environments to earth, make it almost impossible to deny that life outside of our planet and even our solar system is completely plausible. This has been only a brief analysis of the plausibility of extra-terrestrial life looking at only a few environments and organisms. With rapidly advancing technology and space travel, we can only get closer to the answer; are we alone in the universe?
Image credit: http://www.History.com
- Ellis-Evans and D. Wynn-Williams (1996) Antarctica: A great lake under the ice, Nature, Vol 382 p644-646
- Ettwig, M. Butler, D. Paslier, E. Pelletier, S. Mangenot, M. Kuypers, F. Schreiber, et al. (2010). Nitrite-driven anaerobic methane oxidation by oxygenic bacteria. Nature, Vol. 463 p543-548
- Schuerger, R. Ulrich, B. Berry, W. Nicholson (2013) Growth of Serratia liquifaciens under 7mbar, 0°C and CO2-enriched anoxic atmosphere, Astrobiology, Vol. 13, P115-131
- Wachtershauser (1988) Before enzymes and templates: Theory of surface metabolism, Microbiological review, Vol. 52, p452-484
- Wynn-Williams and H. Edwards (2000) Antarctic ecosystems as models for extra-terrestrial surface habitats, Planetary and space science, Vol. 48 p1065-1075