Enceladus is a small, tiny Saturn’s moon with an icy surface, a rocky interior and an ocean of liquid water sandwiched between the two. It’s got plumes, mostly comprised of water, that is shouting out from its south pole. Although Cassini was never designed to look for life in Enceladus ocean, it does have powerful instruments that can be used to look for habitability.

Thanks to it, during the one of Cassini dive in the plumes, scientists manage to detect the presence of molecular hydrogen. Such a discovery, among the others, makes Enceladus a more hospitable environment for life than any other body in our solar system, outside of Earth.

NASA’s depiction of the oceans under Enceladus. Image credit: NASA/JPL-Caltech

Ingredients For Life In One Place

Life needs three elements. It needs water, chemistry, and energy. Some of these lines of evidence are telling us that Enceladus has these three things.

Saturn’s sixth largest moon at around 500 km in diameter is encased in a crust of ice up to 40 km thick, floating atop a vast salty ocean. From afar, Enceladus looks like a smooth, white pearl, but a closer look at its surface, reveals a rougher reality.

Its north pole is riddled with impact craters, scars left over from run-ins with asteroids and other cosmic debris. On its south pole, we see long, aquamarine “tiger stripes”, fractures in the ice that spew tall plumes of water vapor and ice particles kilometers above the surface ( animation below).

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Since 2005, Cassini has been gathering and analyzing materials from these plumes. We know they contain water vapor and traces of nitrogen and methane, but one mission was dedicated to the search for molecular hydrogen. This hydrogen is the smallest molecule that exists in the universe and can tell us about things like hydrothermal activity.

Gas captured during the Cassini’s flyby revealed that these plumes do contain hydrogen gas. This suggests that Enceladus’ rocky core is interacting with the warm waters of the subsurface ocean. Also, this chemical reaction releases energy that organisms can use to drive their metabolism. There are many kinds of “methanogenic” organisms at deep sea hydrothermal vents on Earth that do this, such as chemolithotrophs.

This finding does not mean that life exists there, but it makes life more plausible and potentially quite abundant if a fraction of the hydrogen is used to drive biology, said Jeffrey Kargel, a professor at the University of Arizona.

Time For A New Mission – Enceladus Life Finder

The fact that Enceladus is already known to be a geologically active moon, plus the existence of a global ocean, makes it an even more attractive target for future exploration. Cassini’s mission approaches to its ending and scientists are considering new missions, specially marked to look for a life on a Saturn’s icy moon.

One such a mission is the Enceladus Life Finder (ELF), proposed by astrobiologist in 2015. The ELF mission would search for biosignature and biomolecules in the geysers of Enceladus. If selected by NASA, a launch readiness date of December 31, 2021, may be possible.

Overview of the proposed Enceladus Life Finder mission. Image Credit: Jonathan Lunine/ELF

Whichever mission NASA decides to take, one thing is clear. Enceladus will be further examined since along with Jupiter‘s moon Europa, is the best candidate for life in the solar system.