Year: 2018-19

Frangopol Eraleea, Pantelimon Antonia, Nemeș Vlad, Nicolau Iustina

School: School No 49

City: Bucharest

"Liquid water, energy, organics (carbon compounds), and six elements (sulphur, phosphorus, oxygen, nitrogen, hydrogen, and carbon) are the primordial needs of life as we know it. So, what makes Enceladus so special? This sixth largest moon of Saturn has all these materials, but two – sulphur, phosphorus.

Voyager 2 was the first spacecraft to observe the moon and based on its images, it was discovered that Enceladus has the most reflective surface in the Solar System. This, alongside its white colour, raised the hypothesis that its crust could be formed of ice. Evidence of liquid water however, started to appear in 2005 when Cassini observed plumes of vapour being spewed from Enceladus’ south polar surface. During 10 years of activity, Cassini performed 22 fly-bys through these plumes to analyse their composition, and finally confirmed the existence of a subsurface, Earth-like, salty-water ocean (about 20-25km deep) underneath its icy crust.

Amongst the composition of the salt-water plumes, scientists have discovered both organic and inorganic molecules containing nitrogen, hydrogen, carbon, and oxygen. More recent studies have even indicated the presence of more complex organic molecules (masses of over 200 atomic mass units) on top of the previously discovered simpler organic molecules with just a few carbon atoms (e.g. methane, propane). Scientists thus believe that these are the result of hydrothermal activity that drives complex chemical reactions inside the core of the moon.

But what could cause this Earth-like hydrothermal activity? Simply put, Saturn; with its huge gravitational force, the gas giant is deforming Enceladus as it is orbiting around it, which subsequently exposes the moon to tidal heating (energy being released through the friction of the crust), and libration (a small “wobble” which suggests that the ice crust is entirely detached from the core and thus the ocean is present beneath all of the moon’s surface). Furthermore, Enceladus’ porous core allows water to infiltrate, which then heats up and travels upward, thinning the icy layer at the surface (only about 1-5km deep at south pole) and bursting up to 80km into space, where some particles leave the thin atmosphere (forming Saturn’s Ring E), whilst others fall onto the ground in the form of very fine ice.

But how could life potentially exist in this hostile environment and in what form? First, the ample presence of hydrogen in the water suggests that microbes could obtain energy through methanogenesis (combining hydrogen with carbon dioxide). And what about life as we know it? Until 1977 it was widely believed that such life cannot exist without photosynthesis (converting carbon-containing molecules into energy using light). Nonetheless, this fact was demolished with the discovery of hydrothermal vents at the bottom of the Pacific Ocean where life was abundant. The warm and mineral-rich water allowed invertebrates such as giant tube worms to live through chemosynthesis (converting carbon-containing molecules into energy using inorganic compounds – hydrogen gas/sulphide). Similar life might therefore exist on Enceladus – but are we prepared to discover it?"

Solar System News