The image above shows the interior structure of Europa, a major moon of the planet Jupiter, but the smallest of its four Galilean moons. The band of blue in the picture depicts a 100 km-thick layer of salty water below its ice crust that many researchers now think could contain life forms that extract energy from the nuclear decay of various elements.
It has long been known that several solar system moons harbor liquid oceans beneath their icy crusts, but despite the total lack of empirical data on conditions at the water/mantle interface on Jupiter’s’ moon Europa, some researchers believe that Europa has a higher potential to host alien life forms than other, similar moons.
According to a report published in the journal Scientific Reports, a team of investigators from the University of São Paulo in Brazil have identified conditions in a South African gold mine that appears to be analogous, if not similar to conditions that might exist at the ocean/mantle interface on Europa. Moreover, the researchers have identified a strain of bacteria known as Desulforudis Audaxviator that lives by means of a process known as water radiolysis, which is the dissociation of water molecules by ionizing radiation. Interestingly, its name derives from a quotation that appears in Jules Verne’s novel Journey to the Center of the Earth (1864) in which the story’s hero, Professor Lidenbrock, finds a secret message in Latin referring to the summit of the Icelandic volcano Snæfellsjökull that reads: “Descende, audax viator, et terrestre centrum attinges” (Descend, bold traveller, and you will attain the center of the Earth).
According to Douglas Galante, a researcher from Brazil’s National Synchrotron Light Laboratory (LNLS) and the Astrobiology Research Center (NAP-Astrobio) of the University of São Paulo’s Institute of Astronomy, Geophysics & Atmospheric Sciences, the organization that oversees the research, the conditions in the South African mine are caused by water seeping through cracks in rocks that contain radioactive uranium.
Essentially, the water molecules are broken apart by the radioactive uranium, which creates free radicals such as H+, OH- and others, that in their turn, break down rocks like iron disulfide (pyrite), in a process that produces sulphate. The sulphate is then used by the bacteria to synthesize adenosine triphosphate (ATP), which is the nucleotide that regulates the storage of energy inside living cells, which means that these bacteria are the first terrestrial organisms that are known to live directly off the by-products of nuclear energy.
However, while it is known that Europa’s interior is relatively hot due to powerful tidal interactions with Jupiter, hot water alone is not enough to sustain even bacterial life. According to the researchers, biological processes depend on there being differences in the amounts of molecules, electrons, and ions in different regions to allow for processes, such as cellular respiration, photosynthesis, and ATP production, to occur.
While nothing is currently known about the actual conditions deep inside Europa, researchers are hopeful that hydrothermal emanations (underwater volcanoes) are present on Europa to provide sources of molecular hydrogen [H2], hydrogen sulphide [H2S], sulphuric acid [H2SO4], methane [CH4], and others to create chemical imbalances that can be transformed into meaningful amounts of biological energy.
Nonetheless, despite the promising results of this study many questions remain unanswered, and will likely stay so until at least 2025 when a dedicated mission, code named “Europa Clipper”, will be launched by NASA to study the actual conditions on Europa. No spacecraft has landed on Europa to date, although the Europa Clipper is expected to perform 45 close flybys of the icy moon, and use a number of instruments to determine whether its conditions are suitable for life, including cameras, spectrometers, magnetometer, a thermal instrument, and an ice penetrating radar.