The idea of life existing in a buried sea inside a moon of Jupiter may seem strange, perhaps impossible. But a series of laboratory tests show that some terrestrial bacteria would adapt well to the salty and sulfate-rich ocean believed to exist beneath the hard icy shell of Europa.
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In addition to a global liquid ocean, Europa, which is about one-quarter the diameter of Earth, has a metal-rich core and rocky interior, providing both the chemistry and possible energy sources to support life.
Measurements from NASA's Galileo mission to Jupiter indicate that Europa's ocean is rich in magnesium sulfate, among other salts. That got scientists curious about how well some bacteria that live in harsh environments on Earth would fare under even more extreme conditions that may exist on Europa.
Astrobiologist Sandra Ramirez, with Mexico's Universidad Autonoma del Estado de Morelos, and colleagues tested three strains of bacteria -- Bacillus pumilus, Halomonas halodurans and Salinibacter ruber -- under different concentrations of sodium chloride, magnesium chloride, sodium sulfate and magnesium sulfate.
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The point of the experiment was to demonstrate whether the bacteria have the ability to grow not only in the presence of salty sodium chloride, but also but when "salts of astrobiological interest," as Ramirez puts it, are added.
The researchers found that all three strains of bacteria could adapt to a concentrated saline environment. But one, the extremophile Salinibacter ruber, showed a particular fondness for magnesium sulfate. "We found a very different behavior in the extreme bacteria," Ramirez said at the International Astronautical Congress in Jerusalem. "We're conducting experiments investigating the reason for this."
The initial experiments show that Europa's ocean may harbor life as we know it, despite a myriad of potentially extreme conditions, such as temperature, acidity, pressure and salinity, the researchers conclude.
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Both NASA and the European Space Agency are planning missions to Europa, but neither spacecraft include a lander to directly probe cracks in the moon's icy surface. Still, the new research may help scientists learn what telltale signs of life to look for, particularly if an orbiter can gather samples from a possible water plume that may be shooting into space from Europa's southern pole.
"I think it's very hard to detect bacteria in a plume ... But one idea is to look for biosignatures for this type of bacteria," Ramirez told Discovery News. "You need very specific instruments, but it can be done."