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It is one of the most beautiful objects in our solar system, a shiny sphere of pure white ice that hides a liquid ocean inside.
But despite looking nothing like our planet, Enceladus, Saturn’s sixth largest moon, may have something in common with Earth: the presence of life.
Scientists have discovered organic molecules in the moon’s plumes that could be supporting “communities” of tiny microbes.
Researchers believe that these compounds could promote its metabolism or the formation of amino acids.
Experts already know that there are phosphates, methane, hydrogen and carbon dioxide on Enceladus, all of which are also possible signs of life.
Enceladus, Saturn’s sixth largest moon, is a frozen sphere just 313 miles in diameter (about one-seventh the diameter of Earth’s moon). It is shown in this image captured by NASA’s Cassini spacecraft.
Plumes emanating from Saturn’s moon Enceladus contain compounds including hydrogen cyanide (HCN), acetylene (C2H2), propylene (C3H6) and ethane.
The findings were detailed in a new study led by Jonah Peter, a doctoral candidate in biophysics at Harvard University in Boston.
“Here we present the detection of several additional compounds of great importance for the habitability of Enceladus,” the authors state.
“Our results indicate the presence of a rich and chemically diverse environment that could support complex organic synthesis and possibly even the origin of life.”
Enceladus has an outer layer of ice at least 12 miles thick that covers a liquid ocean of water inside.
Long snake-shaped fractures in its icy surface expel enormous columns formed by grains of ice and water vapor into space.
At least some of these plumes are believed to be frozen drops of the mysterious liquid ocean, possibly a pristine underwater abyss teeming with life forms.
Before ending its mission in 2017, NASA’s Cassini spacecraft not only imaged Enceladus’ plumes but flew directly through them.
Together with his colleagues, Peter studied data from Cassini’s Ion and Neutral Mass Spectrometer (INMS) collected during flybys in 2011 and 2012.
The team used a statistical analysis technique that analyzed billions of potential compositions of the column material.
Enceladus, Saturn’s sixth largest moon, has an outer layer of ice covering an ocean of liquid water. Researchers have detected phosphates in the ice expelled in the form of “plumes.” These columns are made up of water vapor and ice grains that are believed to come from the ocean.
This image imagines a cross section of Enceladus. Note the long fractures in the icy surface that eject plumes. These columns are made up of ice grains and water vapor.
From this, they identified that the most likely composition of the columns are the five molecules already identified: water, carbon dioxide, methane, ammonia and molecular hydrogen.
The fact that the moon is spewing methane gas is exciting because it is an organic molecule typically produced or used by microbial life.
The presence of methane in these plumes has led scientists to hypothesize that microbes may be living, or have lived, beneath Enceladus’ shell.
But the authors found that newly identified molecules of hydrogen cyanide (HCN), acetylene (C2H2), propylene (C3H6) and ethane (C2H6) have also been identified, as well as traces of an alcohol (methanol) and molecular oxygen.
“These compounds could serve as direct substrates for biological growth or be intermediates for other metabolic reactions involving additional organic substances and oxidants,” the team states.
The ability of these compounds to support life on Enceladus depends largely on how diluted they may be in the moon’s subterranean ocean, the authors note.
Cassini appears here in a NASA illustration. Cassini was launched from Cape Canaveral, Florida, in October 1997.
But the team is hopeful that a complex and diverse “hydrothermal environment” exists beneath the moon’s icy outer layer, likely deep beneath the ocean floor.
The presence of acetylene and ethane in the plume further implies “ongoing catalytic reactions” that are being driven by metal-bearing minerals within the ocean.
One day, experts will have made all the assumptions they can make about Enceladus from the Cassini data, and at that point more missions will be necessary.
Determining with certainty whether life exists or has existed on Enceladus could probably be the task of another spacecraft.
Until then, science fiction authors will surely be inspired by the unique geological formation of this frozen world, 500 kilometers from humanity.
“A more detailed examination of Enceladus’ oceanic material will require future robotic missions,” the study authors conclude.
The full findings have been published in Nature Astronomy.