ICE SUBLIMATING OFF THE SURFACE REPLENISHES A TENUOUS ENVELOPE
Planetary astronomers are very interested in exploring the moon Europa in search of life. Slightly smaller than Earth’s moon, Europa orbits Jupiter. Surface temperatures on the icy moon never rise above minus 162 degrees Centigrade. A temperature so cold that water-ice is as hard as rock.
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 issuing through cracks in the surface, as first photographed by the Hubble Space Telescope in 2013.
From archival Hubble observations, spanning 1999 to 2015, 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.