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Selections from 2021: Why We Should Return to Enceladus

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photograph of Saturn's moon Enceladus
The Cassini spacecraft snapped this photo of Enceladus's northern hemisphere in 2008. Perhaps it's time for another visit. [NASA/JPL/Space Science Institute]

Editor’s note: In these last two weeks of 2021, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

The Science Case for a Return to Enceladus

Published July 2021

Main takeaway:

A team led by Morgan Cable (Jet Propulsion Laboratory) proposes that Saturn’s icy moon Enceladus should be the target of a future spacecraft mission. The moon’s water plumes are unique in the solar system and provide unparalleled access to the salty, organic-rich ocean beneath the crust — an environment brimming with astrobiological promise.

Why it’s interesting:

photograph of enceladus with plumes

A backlit view of Enceladus’s south polar plumes. [NASA/JPL-Caltech/Space Science Institute]

Enceladus is only 504 kilometers (313 miles) in diameter — you could drive around it in roughly a day at a leisurely 65 kilometers (40 miles) per hour — but this tiny moon is one of the most promising places to search for life beyond Earth. Its icy crust is dotted with small craters and its southern hemisphere is crossed by several long fissures. As the Cassini spacecraft flew by Enceladus in 2005, it spotted cryovolcanoes erupting through the fissures, spraying water into space. The presence of salt in the plumes indicated that they emerged from an ocean deep enough to reach the moon’s rocky core. Analysis of gravity measurements and observations of Enceladus’s slight wobble confirmed the presence of a global ocean, which is likely to be a persistent rather than transient feature.

What kind of mission would be best:

Given the existing evidence for an organic-rich water ocean, Cable and coauthors say we already know that Enceladus is habitable, so the logical next step is to send a dedicated life-finding mission. It may be possible to probe Enceladus’s oceans in a minimally invasive way by sending a spacecraft to fly repeatedly through its plumes and analyze the droplets. A lander or rover could undertake more sensitive experiments, searching for life-signaling organic molecules like amino acids and lipids. A mission to Enceladus would require roughly 11 years to travel from Earth to its home in orbit around the moon — so what are we waiting for?

Citation

Morgan L. Cable et al 2021 Planet. Sci. J. 2 132. doi:10.3847/PSJ/abfb7a