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Enceladus is the sixth-largest moon of Saturn and a leading candidate for searching for extraterrestrial existence in the Solar System.
Artist’s impression showing NASA’s Cassini spacecraft passing through plumes that are erupting at the south pole. These plumes look a lot like geysers, and release a mixture of water vapor and ice grains. Image credit: NASA / JPL-Caltech.
NASA’s Cassini spacecraft detected evidence of Enceladus’ subsurface ocean in 2014. It also sampled water from eruptions similar to geysers that occurred through cracks in the ice at South Pole.
Robotic probe found methane, and other organic compounds that are essential for life’s foundations.
Regis Ferriere, University of Arizona planet scientist, and his colleagues at the University of Arizona calculated in 2021 that alien life might have existed on Enceladus. This could be why Enceladus’ moon has been producing methane.
Dr. Ferriere stated, “To find out if this is true, we need to go back and examine Enceladus.”
Their new paper reports that Dr. Ferriere with co-authors have found that although the total hypothetical mass of microbes living in Enceladus’ ocean is small, it would still require a spacecraft to visit Enceladus and determine if there are Earthlike microbes under its ocean.
Dr. Ferriere stated, “Clearly sending a robot crawling though ice cracks or deep-diving to the seafloor wouldn’t be an easy task.”
“More realistic missions were designed to use more sophisticated instruments to study the plumes, like Cassini did. Or even land on the surface of the moon.
Cassini’s excess of methane in plumes conjures up images of remarkable ecosystems in Earth’s deep oceans, hydrothermal vents.
Hot magma from below heats the water at the edge of the two adjacent plates tectonic. This creates ‘white smokers’ that spew scorching hot and mineral-saturated seawater.
Organisms cannot get sunlight and must rely on the energy contained in chemicals released by white smokers for their daily existence.
Dr. Ferriere stated that hydrothermal vents on our planet teem in life, large and small, despite the darkness and insane pressure.
“The methanogens, the simplest of living organisms, can power their own energy even without sunlight.”
This graphic shows how Cassini scientists believe water reacts with the rock below Enceladus’ ocean to produce hydrogen gas. Credit: NASA/JPL-Caltech/Southwest Research Institute.
The methanogens are dihydrogen and carbon dioxide convertors, producing methane as an byproduct.
Based on Enceladus’ methanogens, the authors constructed their calculations using the assumption that they inhabit oceanic hydrothermal valves similar to those found on Earth.
They calculated the Enceladus total methanogen mass and the probability that the plumes could eject their organic molecules.
Professor Antonin Affholder at the University of Arizona, said that he was surprised by the fact that the hypothetical abundance of cells could only equal the mass of one whale in Enceladus’ global ocean.
The biosphere of Enceladus may not be as dense. Our models show that the biosphere would still be productive enough for plumes to contain enough organic molecules and cells to allow instruments to pick up any future spacecraft.
It is possible that cells might not be discovered, but it would be unlikely. They would need to be able to survive outgassing and travel through the space-time vacuum.
Researchers suggest instead that detectable organic molecules such as certain amino acids would be indirect evidence in favor or against an environment rich with life.
Dr. Ferriere stated that “considering that the calculations show that any Enceladus life would be very sparse, it’s likely that there won’t be enough organic molecules to conclusively conclude that there is one,”
“So instead of focusing on how much life there is, we asked: “What maximum organic material could exist in an absence of life?”
It could indicate that there is life after all the measurements have been taken.
Dr. Affholder stated that “the definitive evidence of living cell captures on an alien planet may still remain elusive for decades.”
“Until then the truth that we cannot rule out the existence of life on Enceladus for the foreseeable future is the best we can do.”
This study was published by the Planetary Science Journal.
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Antonin Affholder The authors and others. 2022. The Enceladus Deep Ocean’s Methanogenic Biosphere: Biomass and Productivity. Implications for Detection. Planet. Sci. Sci. 3, 270; doi: 10.3847/PSJ/aca275