Does life exist on Europa, the moon of Jupiter that has enticed astrobiologists for decades with signs of a vast and sunless ocean hidden beneath its crust? Data from NASA’s Jupiter-orbiting Juno spacecraft now suggest that if anything does lurk within this moon’s dark abyss, it may be starved of life-giving oxygen.
Despite being a prime target in the hunt for alien life, Europa is not necessarily a nice place to live. A spacesuit-clad astronaut spending 24 hours on its surface could be protected for the duration from the moon’s cold and essentially airless conditions but would still receive a lethal dose of radiation from an incessant rain of high-energy particles whirling through Jupiter’s powerful magnetic field. That constant bombardment has a potential upside, though: it also chips away ever so slightly at the moon’s icy surface, irradiating and splitting apart various molecules to create more complex chemistry. Because most of Europa’s crust is composed of water ice—that is, familiar H2O—this process’s primary byproducts are oxygen and hydrogen that either sticks to the surface or soars aloft to form a tenuous atmosphere around the moon. Some of that material may even seep down into the trapped ocean below, where it could conceivably serve as a source of energy and nutrients for living things.
That makes this frigid shell “like the lung for Europa,” says Jamey Szalay of Princeton University. “It’s constantly generating oxygen over the whole surface.” Just how much oxygen Europa makes, however, has been a mystery—until now. A new study led by Szalay offers best-yet estimates of the moon’s production of molecular oxygen—the form upon which we Earthlings rely—and has found that Europa manufactures it in woefully diminutive amounts. The result suggests that any oxygen making its way within the moon would be a trickle, not a torrent, making the substance’s paucity a potential top-down limit on life’s prospects there.
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