Endowed with a vast ocean under a thick layer of ice, Enceladus, one of Saturn’s 83 moons, is a clear candidate for hosting extraterrestrial life. The mystery of whether microbial extraterrestrial life could inhabit Enceladus could be solved by an orbiting space probe, without the need for a landing on its surface to pierce the ice sheet and access the inland sea, according to the conclusion reached in a new study.
When Enceladus was first flown by, by NASA’s Voyager 1 space probe in 1980, it seemed like an uninteresting “snowball.” Later, between 2005 and 2017, NASA’s Cassini probe flew through the Saturn system and studied Saturn’s complex rings and moons in unprecedented detail. Scientists were stunned when Cassini discovered that Enceladus’s thick ice cap conceals a vast, warm internal ocean of salty liquid water that gives off methane, a gas that on Earth typically originates from microbial life.
Methane, along with other organic substances that make up the building blocks of life, was detected when Cassini flew through gigantic plumes that erupted from Enceladus’s surface and were essentially made up of water vapor and ice particles.
As the small moon orbits the ringed gas giant, Saturn’s immense gravitational field pulls on it, subjecting it to structural stress that creates friction and heats its interior. As a result, spectacular jets of water shoot into space from cracks and crevices in Enceladus’s icy surface.
Artist’s impression of the Cassini spacecraft flying through plumes of ejected material, like geysers, from Enceladus’ south pole. (Image: NASA JPL/Caltech)
Last year, a team of scientists, from the University of Arizona in the United States and the University of Sciences and Letters of Paris in France, calculated that if life could arise on Enceladus, it is very likely that its presence explains why the moon “belches” methane.
Sending a robot to crawl through cracks in the ice sheet and plunge to the bottom of the sea would be perfect, but it would not be an easy task.
In a new study, the team led by Régis Ferrière of the University of Arizona has concluded that although the hypothetical total mass of living microbes in the ocean of Enceladus would be small, a visit from a spacecraft remaining in orbit on Enough time and properly equipped might be enough to tell for sure whether Earth-like microbes populate Enceladus’s ocean beneath its shell of ice.
In the area of Enceladus’s south pole, at least 100 gigantic plumes of water gush through cracks in the icy ground not unlike lava from a volcano on Earth.
Water vapor and ice particles ejected in these plumes, comparable to Earth’s geysers in some ways, are thought to have helped form and maintain one of Saturn’s rings.
Cassini analyzed samples of this ejected material, which includes gases and other particles washed up from the depths of Enceladus’ ocean.
The presence of methane in such material, in proportions apparently greater than those due to known non-biological phenomena operating on Enceladus, evokes the exciting possibility of an ecosystem similar to that sustained around hydrothermal vents in some areas of the seafloor of Enceladus. the Earth, to which light does not reach either. At the locations of such vents, tectonic activity causes magma under the seabed to heat seawater in the porous bedrock, thus creating such vents that spit out very hot, mineral-saturated seawater. Without access to sunlight, the organisms that live there depend on the energy stored in the chemical compounds released by the vents to survive.
On our planet, hydrothermal vents teem with life, large and small, despite the darkness and great pressure. The simplest living beings in this ecosystem are microbes called methanogens.
Methanogens convert dihydrogen and carbon dioxide for energy, releasing methane as a byproduct. Ferrière’s research group made their calculations based on the hypothesis that Enceladus has methanogens that inhabit oceanic hydrothermal vents similar to those found on Earth’s seafloor. The researchers calculated what the total mass of methanogens would be on Enceladus, as well as the probability that cells and especially telltale chemicals (mostly certain amino acids) could be ejected through the plumes.
Calculations indicate that the hypothetical abundance of cells in Enceladus’ global ocean would be great enough to feed the plumes with enough organic molecules or cells to allow some of them to be collected and detected by instruments aboard an orbiter that fly through a plume multiple times to pick up a large enough amount of oceanic material.
The chance of entrapment of cells alive or at least slightly destroyed is low, because such cells would have to survive the process that carries them through a plume from the deep ocean to the vacuum of space. On the other hand, it is reasonably high to capture life-telling amino acids, which would constitute indirect proof of the presence of living beings down there.
The study is titled “Putative methanogenic biosphere in Enceladus’s deep ocean: Biomass, productivity, and implications for detection”. And it has been published in the academic journal The Planetary Science Journal. (Fountain: NCYT de Amazings)