Finding life beyond Earth is the tacit motive behind our current fascination with exoplanets. “Another Earth” is now almost a cliché, though it’s wise to be chary of that phrase. That’s because many writers and even some researchers label an exoplanet as “earthlike” if it lies at the correct distance from its parent star to allow for liquid water. Others use the criterion of the exoplanet matching our size. Or some other similarity.
But cutting through such thickets, life began in Earth’s oceans, so simply discovering extraterrestrial water is enough to make us pay attention. And we do. The nearest body of water is on the Jovian moon Europa.
Jupiter is about to pass behind the Sun so it’s basically lost in daytime solar glare. By late June, early risers will start seeing that brilliant planet in the east before dawn as a morning star. But when thinking of that giant world and its strange moon Europa and remembering it’s probably the likeliest place for ET life, we should be aware that in just a few months, in October, NASA will launch its Europa Clipper mission that will repeatedly fly past it for close-up observations.
Europa is covered with ice sheets found by the Pioneer and Voyager spacecraft in the 1970’s. These float over vast oceans, and since later spacecraft revealed the wispy signature of sodium atoms hovering above Europa, the oceans are apparently warm salt water. The implications are stunning.
The heat that keeps this water liquid comes from friction generated by massive Jupiter and from Europa’s physical distortions created by regular tidal pulls from the three other huge Jovian moons. You see, the four giant satellites first seen by Galileo in 1609 orbit in sync. Io circles Jove four times in the same period in which Europa orbits twice and Ganymede orbits once. They keep meeting up, which is easily seen through any backyard telescope.
NASA’s Europa Clipper mission will of course be unmanned. Europa’s surface gets a steady 540 rads of daily radiation, enough to kill a human in two days. Although space enthusiasts had been hoping for a lander that could burn or drill through the ice to probe the ocean below, it’s sensible to first send this orbiter whose exquisite instrumentation will photograph and examine Europa in close-up detail, determining things like the thickness of that ice.
But someday we’ll drill down and see what, if anything, swims or floats in the warm Europian seas.
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