Space

Complex organic molecules strengthen the case for life on Saturn's watery moon

New analysis of Cassini data has found evidence of complex organic molecules in the spray from its subsurface ocean 
New analysis of Cassini data has found evidence of complex organic molecules in the spray from its subsurface ocean 
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A diagram detailing the internal composition of Enceladus, and how the complex organic molecules make their way into space from the core of the moon
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A diagram detailing the internal composition of Enceladus, and how the complex organic molecules make their way into space from the core of the moon
A Cassini image from 2010 of the water vapor plumes spraying through the cracks in the icy shell, at the south pole of Enceladus
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A Cassini image from 2010 of the water vapor plumes spraying through the cracks in the icy shell, at the south pole of Enceladus
New analysis of Cassini data has found evidence of complex organic molecules in the spray from its subsurface ocean 
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New analysis of Cassini data has found evidence of complex organic molecules in the spray from its subsurface ocean 
Saturn's moon Enceladus is one of the most promising places in the Solar System to look for extraterrestrial life
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Saturn's moon Enceladus is one of the most promising places in the Solar System to look for extraterrestrial life

Saturn's moon Enceladus is one of the most promising places in the Solar System to look for extraterrestrial life. We already knew it has many of the necessary ingredients, and now a new study has ticked off another box on the list. Cassini mission data has shown the presence of complex organic molecules, spraying up from the moon's subsurface ocean through cracks in the icy shell.

The first inkling that Enceladus might be home to an ocean of water came in 2005, when Cassini detected jets of water vapor and ice spraying up from beneath the moon's surface. Later observations noted gravity fluctuations that suggested a smallish ocean beneath its south pole, while a 2015 study found that its "wobble" indicated the ocean might be global. Hydrothermal vents at the bottom of this ocean could create very life-friendly conditions.

Over the years it was running, Cassini performed several dives through the icy plumes. Previous analysis of that data found the signature of hydrogen gas, which NASA scientists said could make the moon "a candy store for microbes." The new study lends even more weight to the possibility of life on Enceladus, with the detection of more complex organic molecules.

A Cassini image from 2010 of the water vapor plumes spraying through the cracks in the icy shell, at the south pole of Enceladus
A Cassini image from 2010 of the water vapor plumes spraying through the cracks in the icy shell, at the south pole of Enceladus

Cassini's dust-analyzing instrument picked up the molecule fragments as they jetted away from Enceladus at up to 30,000 km/h (18,640 mph). The fragments weighed up to 200 atomic mass units, but the team believes that they might have weighed thousands prior to colliding with the spacecraft.

"We found large molecular fragments that show structures typical for very complex organic molecules," says Nozair Khawaja, co-lead author of the study. "These huge molecules contain a complex network often built from hundreds of atoms of carbon, hydrogen, oxygen and likely nitrogen that form ring-shaped and chain-like substructures."

A diagram detailing the internal composition of Enceladus, and how the complex organic molecules make their way into space from the core of the moon
A diagram detailing the internal composition of Enceladus, and how the complex organic molecules make their way into space from the core of the moon

The researchers suggest that these complex organic molecules are forged through hydrothermal activity, as material from the porous rocky core is ejected into the ocean. From there, gas bubbles carry them up to the surface, where they form a thin organic film under the ice. In the vents, where the water's surface is open to space, these bubbles burst, spraying the familiar plumes of water vapor, ice and organic molecules.

"It is the first ever detection of complex organics coming from an extraterrestrial water-world," says Frank Postberg, co-lead author of the study. "In my opinion the fragments we found are of hydrothermal origin, having been processed inside the hydrothermally active core of Enceladus: in the high pressures and warm temperatures we expect there, it is possible that complex organic molecules can arise."

This newest find will no doubt make Enceladus an even more enticing place to continue the search for extraterrestrial life.

The research was published in the journal Nature.

Source: ESA

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