Study: Search For Life On Europa Takes An Acid Bath

It has been long speculated that the Jovian moon Europa might support life, given that it is believed to harbor an ocean under its ice-encrusted surface. But researchers now believe that the satellite's ocean might be too acidic to sustain life.

Astrobiologists studying the massive moon Europa have detected chemicals on its surface that might throw a damper on the theory that living organisms, at least those that exist within the parameters of human understanding, might flourish there. Just months after finding evidence that pointed to conditions that might sustain living organisms, scientists have found strong oxidants that, if they were to drift downward through Europa's hypothesized oceans, would make the waters far too acidic to maintain life.

According to Matthew Pasek, a University of South Florida astrobiologist, the resulting level of acidity in the Europan ocean "is probably not friendly to life — it ends up messing with things like membrane development, and it could be hard building the large-scale organic polymers."

As Charles Q. Choi at Space.com explains, oxidants are compounds that have the ability to receive electrons from other compounds. They are rare in the Solar System due to the presence of reductants like carbon and hydrogen, which react with oxidants to form oxides like water and carbon dioxide.

However, the surface of Europa is rich in strong oxidants like oxygen and hydrogen peroxide, compounds that most likely make their way down to and into the oceans through the same volatile activity that causes water to rise up from below. Whereas small amounts of oxidants are beneficial to organic constructs due to its oxygen content, researchers believe that an extended period of oxidants entering the ocean in substantial amounts (for example, half the lifetime of Europa itself) would have a detrimental impact on the formation and sustainability of living organisms. The oxidants would possibly react with sulfides and other compounds to form a corrosive environment akin to the "average soft drink."

Pasek says that although such a sequence of events does not completely obviate the possibility of living organisms forming and prospering, it does suggest that for them to do so, they would have to evolve at an accelerated rate to offset and/or tolerate the acidification. As an example, Pasek points to the extremophiles that developed in the acidic mine drainage environment in the Rio Tinto river in Spain.

Calcium-based skeletal and exo-skeletal systems are highly susceptible to dissolving when exposed to acid, so some other form of skeletal structure would have had to develop. Pasek suggests, along with co-author Richard Greenberg, that the bones of a thriving organism might be made of vivianite.

Pasek said that "one of the interesting possibilities is that they might have used blue phosphates as their bone material instead to evolve large organisms. If you have iron phosphates, you make a pretty blue mineral called vivianite."

Pasek and Greenberg's findings, which were published in the Jan. 27 edition of Astrobiology, are part of the many contributions being made in the ongoing effort to understand life and its myriad possibilities in the universe, including humanity's place in it.

The search for habitable planets is an aspect of astrobiology that garners considerable press, not to mention considerable speculation not only among scientists but among the public at large. It would seem that there is a biological imperative to establish whether or not there are others that inhabit the universe alongside humanity and its fellow Earthbound organisms. As the methods of detection have become more reliable and corroborative, the number of extra-solar planets -- or exoplanets -- discovered within the last few years has increased enormously. According to the Extra-Solar Planets Encyclopedia, there are now 760 worlds that have been detected and confirmed as existing outside our Solar System. Of those, only a few are in what is known as the "Goldilocks Zone," or the habitable zone are a parent star most conducive to supporting life as we understand it.

Like Pasek's and Greenberg's work, others look into various systems and conditions that might be conducive to supporting life on other worlds. For example, researchers at the NASA Ames Research Center and Tokyo University suggested in September that the habitable zone might be stretched a bit to incorporate more arid worlds, much like the one found in Frank Herbert's science fiction classic, Dune.

(photo credit: Rob Lavinsky, Creative Commons)

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