Credit: NASA, NASA-JPL, University of Arizona

You would think that living ½-billion miles from the Sun would be no place to call home. But planetary astronomers are very interested in exploring the moon Europa in search of life. Slightly smaller than Earth's moon, Europa orbits monstrous Jupiter. Surface temperatures on the icy moon never rise above a frigid minus 260 degrees Fahrenheit. A temperature so cold that water-ice is as hard as rock.

Yet, beneath the solid ice crust there may be a global ocean with more water than found on Earth. And, where there is water, there could be life. Like a leaky garden hose, the ocean vents water vapor into space from geysers poking through cracks in the surface, as first photographed by the Hubble Space Telescope in 2013.

The latest twist comes from archival Hubble observations, spanning 1999 to 2015, which find that water vapor is constantly being replenished throughout one hemisphere of the moon. That's a bit mysterious. Nevertheless, the atmosphere is only one-billionth the surface pressure of Earth's atmosphere.

The water vapor wasn't seen directly, but rather oxygen's ultraviolet spectral fingerprint was measured by Hubble. Oxygen is one of the constituents of water. Unlike the geysers, this water vapor is not coming from Europa's interior, but rather sunlight is causing the surface ice to sublimate. A similar water vapor atmosphere was recently found on the Jovian moon Ganymede.

Europa is so exciting as a potential abode of life it is a target of NASA's Europa Clipper and the Jupiter Icy Moons Explorer (JUICE) of the European Space Agency – planned for launch within a decade.

Provider: Space Telescope Science Institute

Image Source: https://hubblesite.org/contents/news-releases/2021/news-2021-057

Curator: STScI, Baltimore, MD, USA

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