Rick Robinson

Dec 11th 2020

Jupiter’s Moon Europa: A Moon With an Ocean — and Possibly Life

What does ordinary table salt have to do with Jupiter’s moon Europa and the destination of NASA‘s upcoming Europa Clipper interplanetary mission?

As often happens in space science, the answer to this question is straightforward, but the implications are breathtaking. The detection of sodium chloride on the surface of Europa lends support to the theory that Europa not only has an underground ocean, but that this ocean contains the building blocks of life, and perhaps its own ecosystem of living organisms.

All of which means that the Europa Clipper mission just might provide the first direct evidence that perhaps we are not alone.

Misbehavior of the Gods

First, a little background. As recounts, the four large moons of Jupiter, including Europa, were discovered by Galileo using his homemade telescope in January 1610. They are still collectively called the Galilean moons, but he simply numbered them.

As Business Insider tells us, it fell to another astronomer to give them individual names. That astronomer, Simon Marius chose to name them for four of the Roman mythological god Jupiter’s many romantic conquests. In order of distance from Jupiter, they are Io, Europa, Ganymede and Callisto.

And as Business Insider also wryly notes, NASA is not above a little scientific mythology of its own. Another mission currently investigating Jupiter and its moon system is named Juno, after Jupiter’s mythological (and very jealous) wife.

Science Fiction Lends a Hand, and So Does NASA

By the early 20th century, a new scientific mythology took form: science fiction. The moon and Mars usually played the starring role in early science fiction, but as Popular Science details, the four big moons of Jupiter, including Europa, got their share of attention.

That is about where things stood until the 1970s, when space missions provided our first close-up views of these distant worlds — and spectacular views they were. As describes, each of the four big moons turns out to have very different surface features: from Io, the most volcanically active object in the solar system, to Callisto, the most heavily cratered.

Europa does not have volcanoes and practically no craters. In fact, scientists determined that the surface of Europa cannot be more than about 160 million years old (even though Europa itself is nearly as old as the solar system, about 4.5 billion years).

Some force, it seems, is continually “repaving” the surface of Europa. Not only is the surface being continually renewed; it is also almost completely flat. The most conspicuous surface features are linear markings, like scratches or cracks.

A Hidden Ocean …

One type of force, gravitational tides, turns out to account for both Io’s volcanoes and Europa’s flat, cracked surface. Tidal forces generated by Jupiter itself and the other moons subject all of the moons to flexing, which, over millions of years, heats them up internally.

Thus, the inner moons, especially — Io and Europa — are much warmer internally than you would expect of worlds so far from the sun. When they formed, much of their material was water ice. The interior of Io is so hot that the ice long ago vaporized and escaped into space.

Europa, not so close to Jupiter, only got hot enough to melt the ice. Per, the result was and is a layer of liquid water believed to be as much as 60 miles deep — several times deeper than the deepest spot in Earth’s oceans. A thin layer of ice, only a few miles thick at most, covers this ocean, which contains more water than all of Earth’s oceans combined.

… Of Salt Water

All of which brings us back to that recent detection of sodium chloride (or in layman’s terms, table salt) on Europa. Liquid water anywhere always gets the attention of researchers, because it seems to be an ideal environment for life. But water by itself is not enough: For life, you also need its building blocks and nutrients, most of which are to be found in rocks.

If Europa’s underground ocean is salt water, reports, it must be in contact with rock, and surely contains many other dissolved substances, making the prospects for life that much stronger.

And for a final touch, says Scientific American, these results indicate that liquid water must sometimes reach very close to the surface, or even break through before freezing, which could make detecting life on Jupiter’s moon Europa that much easier.