Universe Today
For decades, ever since the
Pioneer
and
Voyager
missions passed through the outer Solar System, scientists have speculated that life might exist within icy bodies like Jupiter's moon
Europa
. However, thanks the
Cassini
mission, scientists now believe that other moons in the outer Solar System - such as Saturn's moon
Enceladus
- could possibly harbor life as well.
For instance,
Cassini
observed plume activity coming from Enceladus' southern polar region that indicated the presence of hydrothermal activity inside. What's more, these plumes contained organic molecules and hydrated minerals, which are potential indications of life. To see if life could thrive inside this moon, a team of scientists
conducted a test
where strains of Earth bacteria were subjected to conditions similar to what is found inside Enceladus.
The study which details their findings recently appeared in the journal
Nature Communications
under the title "
Biological methane production under putative Enceladus-like conditions
". The study was led by Ruth-Sophie Taubner from the University of Vienna, and included members from the Johannes Kepler University Linz,
Ecotechnology Austria
, the University of Bremen, and the University of Hamburg.
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Artist's rendering of possible hydrothermal activity that may be taking place on and under the seafloor of Enceladus. Credit: NASA/JPL
[/caption]
For the sake of their study, the team chose to work with three strains of methanogenic archaea known as methanothermococcus okinawensis. This type of microorganism thrives in low-oxygen environments and consumes chemical products known to exist on Enceladus - such as methane (CH
4
), carbon dioxide (
CO2
) and molecular hydrogen (H
2
) - and emit methane as a metabolic byproduct. As they state:
These strains were selected because of their ability to grow in a temperature range that is characteristic of the vicinity around hydrothermal vents, in a chemically defined medium, and at low partial pressures of molecular hydrogen. This is consistent with what has been observed in Enceladus' plumes and what is believed to exist within the moon's interior.
These types of archaea can still be found on Earth today, lingering in deep-see fissures and around hydrothermal vents. In particular, the strain of
M. okinawensis
has been determined to exist in only one location around the deep-sea hydrothermal vent field at Iheya Ridge in the Okinawa Trough near Japan. Since this vent is located at a depth of 972 m (3189 ft) below sea level, this suggests that this strain has a tolerance toward high pressure.
[caption id="attachment_92503" align="aligncenter" width="580"]
Hydrothermal vents on Earth's ocean floor. Credit: NOAA
[/caption]
For many years, scientists have suspected that Earth's hydrothermal vents played a vital role in the emergence of life, and that similar vents could exist within the interior of moons like Europa,
Ganymede
,
Titan
, Enceladus, and other bodies in the outer Solar System. As a result, the research team believed that methanogenic archaea could also exist within these bodies.
After subjecting the strains to Enceladus-like temperature, pressure and chemical conditions in a laboratory environment, they found that one of the three strains was able to flourish and produce methane. The strain even managed to survive after the team introduced harsh chemicals that are present on Enceladus, and which are known to inhibit the growth of microbes. As they conclude in their study:
From this, they determined that some of the methane found in Enceladus' plumes were likely produced by the presence of methanogenic microbes. As Simon Rittmann, a microbiologist at the University of Vienna and lead author of the study, explained in an interview with
*The Verge*
. "It's likely this organism could be living on other planetary bodies," he said. "And it could be really interesting to investigate in future missions."
[caption id="attachment_136960" align="aligncenter" width="448"]
Artist impression of an interior cross-section of the crust of Enceladus, which shows how hydrothermal activity may be causing the plumes of water at the moon's surface. Credits: NASA-GSFC/SVS, NASA/JPL-Caltech/Southwest Research Institute
[/caption]
In the coming decades, NASA and other space agencies plan to send multiple mission to the Jupiter and Saturn systems to investigate their "
ocean worlds
" for potential signs of life. In the case of Enceladus, this will most likely involve a lander that will set down around the southern polar region and collect samples from the surface to determine the presence of biosignatures.
Alternately, an orbiter mission may be developed that will fly through Enceladus' plumes and collect bioreadings directly from the moon's ejecta, thus picking up where
Cassini
left off. Whatever form the mission takes, the discoveries are expected to be a major breakthrough. At long last, we may finally have proof that Earth is not the only place in the Solar System where live can exist.
Be sure to check out John Michael Godier's video titled "Encedalus and the Conditions for Life" as well: