Saturn’s icy moon Enceladus is one of the likeliest spots to harbour alien life in our solar system - and we wouldn’t need to land to find it, a study has suggested.
Instead, an orbiting space probe would be enough to work out whether life lurks beneath Encedladus’s icy surface.
Geyser-like plumes of ice which erupt from the surface of Enceladus have offered hints that life could lurk in the moon’s subsurface ocean.
NASA’s Cassini probe sampled a plume of material erupting from Enceladus’s surface and found that Enceladus' thick layer of ice hides a vast, warm saltwater ocean outgassing methane – a gas that typically originates from microbial life on Earth.
Régis Ferrière, senior author of the new paper and associate professor in the University of Arizona Department of Ecology and Evolutionary Biology, said: "We must go back to Enceladus and look.”
The new paper was published in the Planetary Science Journal.
Ferrière and his collaborators suggest that the hypothetical total mass of living microbes in Enceladus' ocean would be small, a visit from an orbiting spacecraft is all that would be needed to know for sure whether Earth-like microbes populate Enceladus' ocean.
Ferrière said: "Clearly, sending a robot crawling through ice cracks and deep-diving down to the seafloor would not be easy..
"By simulating the data that a more prepared and advanced orbiting spacecraft would gather from just the plumes alone, our team has now shown that this approach would be enough to confidently determine whether or not there is life within Enceladus' ocean without actually having to probe the depths of the moon.”
Located about 800 million miles from Earth, Enceladus completes an orbit around Saturn every 33 hours.
Along the moon's south pole, at least 100 giant water plumes erupt through cracks in the icy landscape much like lava from a violent volcano.
Scientists believe that water vapour and ice particles ejected by these geyser-like features contribute to one of Saturn's iconic rings.
The excess methane Cassini detected in the plumes conjures images of extraordinary ecosystems found in the lightless depths of Earth's oceans: hydrothermal vents.
Hot magma below the seafloor heats the ocean water in porous bedrock, creating "white smokers", vents spewing scorching hot, mineral-saturated seawater.
With no access to sunlight, organisms depend on energy stored in chemical compounds released by the white smokers to make a living.
Ferrière said: "On our planet, hydrothermal vents teem with life, big and small, in spite of darkness and insane pressur.
“The simplest living creatures there are microbes called methanogens that power themselves even in the absence of sunlight."
Methanogens convert dihydrogen and carbon dioxide to gain energy, releasing methane as a byproduct.
Ferrière's research group modelled its calculations based on the hypothesis that Enceladus has methanogens that inhabit oceanic hydrothermal vents resembling the ones found on Earth.
The researchers calculated what the total mass of methanogens on Enceladus would be.
Antonin Affholder, a postdoctoral research associate at UArizona wrote, "We were surprised to find that the hypothetical abundance of cells would only amount to the biomass of one single whale in Enceladus' global ocean,.
“Enceladus' biosphere may be very sparse. And yet our models indicate that it would be productive enough to feed the plumes with just enough organic molecules or cells to be picked up by instruments onboard a future spacecraft."
"Our research shows that if a biosphere is present in Enceladus' ocean, signs of its existence could be picked up in plume material without the need to land or drill, but such a mission would require an orbiter to fly through the plume multiple times to collect lots of oceanic material."
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