Tiny grains of rock detected by the international Cassini spacecraft orbiting Saturn point to hydrothermal activity on the seafloor of its icy moon Enceladus. This is a very important discovery, which adds to the tantalising possibility that the moon could contain environments suitable for living organisms.
Understanding the interior structure of 500 km-diameter Enceladus has been a top priority of the Cassini mission since 2005, when plumes of ice and water vapour were discovered jetting from fractures at the moon’s south pole.
Now, following an extensive, four-year study of data from the spacecraft, combined with computer simulations and laboratory experiments, scientists have been able to gain deeper insights into the chemical reactions taking place on the floor at the base of Enceladus’s ocean.
Using Cassini’s Cosmic Dust Analyser, scientists have discovered a population of tiny dust grains, just 2–8 nm in radius, in orbit around Saturn. They are rich in silicon, marking them out from the water-ice particles that dominate in the planet’s environment, including in its famous ring system.
Scientists believe that these silicon-rich grains originate on the seafloor of Enceladus, where hydrothermal processes are at work. On the seafloor, hot water at a temperature of at least 90 degrees Celsius dissolves minerals from the moon’s rocky interior. The origin of this energy is not well understood, but likely includes a combination of tidal heating as Enceladus orbits Saturn, radioactive decay in the core and chemical reactions.
“This moon has all the ingredients – water, heat, and minerals – to support habitability in the outer Solar System, confirming the astrobiological potential of Enceladus”, added Nicolas Altobelli, ESA’s Cassini project scientist.
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