Sulphur Bacteria in Mid-Ocean Hot Springs and Possible Life on Saturn’s Moons

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Tube worms in deep sea vents enjoy a long life in ocean floor smoker vents. Image courtesy of University of Washington; NOAA/OAR/OER

The odd animals inhabiting hot springs in the deep oceans, and subglacial ecosystems in polar regions, may have been living there since at least the Late Cretaceous Period – simply because of their strangeness.

Almost every one of the animals discovered in these extreme environments were new to science when found, and cannot live elsewhere.

The vent animals, for example, are not just different species from other deep sea animals; scientists actually needed place them into new phyla simply to accommodate their strangeness.

Could extremophile bacteria indicate the possibility of similarly alien life forms in the unforgiving and extreme climates of other planets, or their moons?

The Chemolithotrophic Bacteria in Galapagos Hot Springs Tubeworms

In 1977, when divers in the submersible Alvin found the waters of the Galapagos hot springs teeming with sulphur-eating bacteria, they quickly concluded that chemosynthetic bacteria must be the nutrient that supported this new ecosystem.

Chemosynthesis is the process by which organisms use inorganic molecules as a source of energy, rather than the sunlight used in photosynthesis.

When scientists examined the giant tubeworms Riftia pachyptila, they found neither a mouth nor a gut – this meant that the giant tubeworms were an entirely new kind of organism.

An entire community of animals in symbiosis with chemolithotrophic bacteria, feeding by means of geochemistry, was an exciting new find, and revealed that extremophile organisms could survive in environments lethal to most living organisms.

Polar Extremophiles

Subglacial microbial communities have survived in cold, darkness and absence of oxygen for a million years in McMurdo Dry Valleys, Antarctica: Image by Zina Deretsky, US NSF

Freezing-cold polar environments on Earth also harbor extremophile bacteria; extremophiles are found in glaciers and on high altitude peaks, fully functioning in these extreme environments.

Titan’s South Pole clearly shows a methane lake. NASA/JPL Space Science Institute

Life on Saturn’s Moons: Enceladus, Titan, and Jupiter’s Europa?

Understanding the oddities of life in our most extreme regions leads us to wonder: is life on Enceladus, Titan, or Europa possible?

  • Enceladus is the brightest moon in our solar system. It is  composed entirely of ice, fully reflecting light. In 2005, the Cassini spacecraft photographed geysers of ice and water vapour being expelled at least 300km into space, so there must be liquid water under the moon’s icy surface, and sufficient heat internally to propel ice into water vapour.
  • Titan is the only moon in our Solar System that has a substantial atmosphere (it is mostly nitrogen). When the Cassini spacecraft dropped the Huygens probe into Titan’s atmosphere, the probe found ammonia and methane. Lakes of methane are clearly visible, as you can see from the image above. Ammonia and methane could theoretically combine, in an electrically charged environment, to make organic compounds, and extremophile bacteria, similar to those found in deep ocean hot springs, could survive in this methanological system.
  • Europa, the second moon of Jupiter, has an icy surface with a suspected liquid ocean below the surface. Life similar to that of subglacial regions is possible on Europa as well.

Extremophiles Provide Insight into Potential Off-Planet Life Forms

Deep ocean hot springs and sub-glacial regions harbor extremophile bacteria, and Enceladus, with abundant water vapour geysers; Titan, with a methane and nitrogen atmosphere; and Europa, with its icy surface, could theoretically harbor extremophiles as well.

The potential for life occurring twice in our Solar System is exciting; Cassini’s ongoing mission to photograph Titan’s surface may provide more insight over time.

References

NASA. Cassini Solstice Mission. (2012). Accessed July 22, 2012.

Museum of Science. Extremophile Bacteria in the Arctic Circle and on Titan. (2010). Accessed July 22, 2012.

Kunzig, R. Mapping the Deep, The Extraordinary Story of Ocean Science. (2000). W. W. Norton & Company/Sort of Books.

Cavanaugh, Colleen et al. Prokaryotic Cells in the Hydrothermal Vent Tube Worm Riftia pachyptilaJones: Possible Chemoautotrophic Symbionts. (1981). Science. 213 (1981): 340-342. Accessed July 22, 2012.

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