Life may be present on Enceladus

Cassini–Huygens Journey to Saturn 

Titan rocket liftoff with Cassini-Huygens payload
15 October 1997
Credit: (NASA)

Two Cassini flyby missions in 2005 provided an unprecedented window into possible markers of life on Enceladus, an icy moon of Saturn. In 1997, the Cassini–Huygens spacecraft was launched on an epic interplanetary expedition that brought it into orbit around Saturn seven years later. The outbound voyage included flyby missions to study Earth, Venus, and Jupiter along the way. Months after entering Saturn’s orbit, the Huygens lander deployed to the surface of Titan, the largest moon of Saturn, and the only moon anywhere known to have a dense atmosphere. Meanwhile, the Cassini orbiter has remained in the Saturn system. Cassini's journey will end with a bittersweet final set of close orbits of Saturn and descent into the planet’s atmosphere in the fall of 2017.

Icy Geysers of Enceladus

As one of the most exciting findings of this decades long set of missions, Cassini found jets of icy particulate matter spewing from the southern polar region of Enceladus. Spectroscopic analysis of these plumes, shooting thousands of miles into space, found water vapor, methane, and other simple organic compounds. Moreover, thermal analysis of the region showed that it was warmer than expected, adding to the evidence for liquid water beneath the surface. Based on the these findings, astrobiologists now propose the possibility of life under the icy crust of this distant moon. They published their results in the journal Astrobiology. If there is life on Enceladus, it is not clear if it evolved there independently or if it might have arrived from beyond.

Enceladus plume molecules detected by Cassini
By NASA/JPL/SwRI (Public domain), via Wikimedia Commons

Birth of a ring of Saturn

Interestingly, much of the material ejected by these plumes does not fall back to the surface of Enceladus. Instead, it falls into a wider orbit around Saturn, making up part of the planet's E ring. This wide outer ring consists of sparsely distributed material that seems to be constantly replenished. Over geological spans of time, organisms could be scattered beyond the E ring, through collisions with asteroids or comets for example. Already capable of surviving extreme conditions, these lifeforms could wind up distributed to other moons in the Saturn system or even Earth. Life may be widely spread over galactic distances in space though a process known as panspermia. It may seem unlikely that living organisms could survive in such a hostile realm as that beneath the surface of Enceladus. In the absence of sunlight, below an icy crust,  there would be no possibility of photosynthesis. However, there are multiple such sunless regions on Earth where life thrives.  These ecosystems run on heat, energy, and minerals created by geologic processes from deep within the Earth itself. Tidal and thermal forces deep within Enceladus generate heat that could support life.

Life on Enceladus

Icy jets from Enceladus
(NASA/JPL), via Wikimedia Commons

If life reached Enceladus hitch-hiking from elsewhere in the Universe, it could arrive ready to grow. Life could also evolve independently on Enceladus. For life to have independently developed from basic building blocks, scientists estimate it might have taken between 10 million to 500 million years.  That is a long time, but consider that Saturn is 4.5 billion years old.  It probably took millions of years for the ocean on Enceladus to freeze over.  That means that life could have evolved on Enceladus or arrived there from some unknown quarter while this ocean still flowed as liquid water.

Next steps

Future missions to Enceladus and other icy moons of the outer planets may prove the existence of life. We should also consider that the presence of water on these distant outposts could be important for future bases of human exploration.

Like it or not, Ice Moon Station will continue to publish articles about Enceladus.
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