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Alan Stahler: A home for life, nearby?

The surface of Jupiter’s moon Europa is nearly pure ice, but for some dark rocky material. Lines are cracks in the ice.
Galileo Project, JPL, NASA |

The next-to-last chapter of an intro-to-astronomy text often deals with the beginning of time, the end of the universe — stuff like that. The final chapter almost always deals with biology: How might life have begun on Earth? Might life exist elsewhere? Are we alone?

During a teleconference Monday, NASA announced new findings that could touch on the aloneness question.

Ordinary table salt is sodium chloride — atoms of sodium and chlorine that stick to each other like laundry, fresh out of the dryer. The atoms stick for much the same reason as the laundry — electricity.



The nerve cells that carry messages within our brains and throughout our bodies rely on sodium atoms flooding into them when they fire — when they’re turned on. (Those sodiums must then be pumped out, before the cell can fire again. Roughly one fifth of all our energy — one out of every five bites of food — goes into pumping sodium.)

Our reliance on sodium is why we need salt. Meat-eaters get salt from their food; herbivores look for salt licks — salty minerals.




To separate sodium atoms from chlorines in salt, one could melt the salt, by heating it to 1,474 degrees Fahrenheit.

Or one could simply dissolve the salt. Water separates atoms, one from another, at a comfortable body temperature. Which is why liquid water is essential to life.

On a planet far from its star, all water is frozen solid; on a planet close to its star, all water is steam. In-between is a “goldilocks zone” — a habitable zone — where water could remain liquid, and might support life.

Half-a-billion miles from the sun, the surface of Jupiter’s moon Europa is nearly pure ice. But when the Galileo spacecraft, orbiting Jupiter, flew past Europa, it found something odd.

Nearly all the electricity we use today is generated by spinning a conductor, such as copper wire, through a magnetic field. Galileo found that, as Europa moves through Jupiter’s magnetic field, it generates electricity. There must be a conductor buried inside Europa.

You cannot make an electrical generator out of ice — ice does not conduct electricity. But saltwater does.

But so far from the sun, how could Europa possibly harbor liquid saltwater?

Bend a paperclip back and forth, until it breaks. Now touch the broken ends to your lip. They’re hot. Internal friction, within the metal, generates heat.

As Europa orbits Jupiter, the giant planet’s gravity flexes the rock in the moon’s heart. Internal friction melts some of Europa’s ice. Beneath hundreds of miles of ice, Europa harbors a liquid, saltwater ocean.

Could there be life, or the sorts of chemicals that could lead to life, floating in Europa’s ocean? We need a water sample. But drilling through hundreds of miles of ice on an alien world is, for the moment, beyond our capabilities.

If a planet has an atmosphere and a magnetic field, it will have an aurora — northern lights. Several years ago, astronomers found evidence for water in the glow of Jupiter’s aurora.

Now, Hubble has found yet more evidence that, near Europa’s south pole, Europan ocean water somehow makes its way to the surface and blows out into space.

It appears that Europa is sending water samples, from hundreds of miles down, out into space — water we do, or soon will, have the capability to collect.

Al Stahler’s science programs can be heard on KVMR (89.5 FM). He brings an enjoyment of science and nature to students of all ages and may be reached at stahler@kvmr.org.


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