Hubble Finds First Evidence of Water Vapour at Jupiter's Moon Ganymede

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OXYGEN FOUND ON THE FROZEN WORLD IS LINKED TO SUBLIMATING SURFACE ICE

Though larger than the blistering planet Mercury, the Jovian moon Ganymede is no place to go sunbathing. Located ½-billion miles from the Sun, the water ice on its surface is frozen solid in frigid temperatures as low as minus 300 degrees Fahrenheit. This makes the ice as hard as rock. Still, a rain of charged particles from the Sun is enough to turn the ice into water vapor at high noon on Ganymede. This is the first time such evidence has been found, courtesy of the Hubble Space Telescope’s spectroscopic observations of aurora on Ganymede spanning two decades. The auroras are used to trace the presence of oxygen, which then is linked to the presence of water molecules sputtering off the surface. Ganymede has a deep ocean located an estimated 100 miles below the surface. That's too deep for water vapor to be leaking out.

Hubble's View of Ganymede in 1996
For the first time, astronomers have uncovered evidence of water vapor in the atmosphere of Jupiter's moon Ganymede. This water vapor forms when ice from the moon's surface sublimates — that is, turns from solid to gas
Scientists used new and archival datasets from NASA's Hubble Space Telescope to make the discovery, publish ed in the journal Nature Astronomy. 

Previous research has offered circumstantial evidence that Ganymede, the largest moon in the solar system, contains more water than all of Earth's oceans. However, temperatures there are so cold that water on the surface is frozen solid. Ganymede's ocean would reside roughly 100 miles below the crust; therefore, the water vapor would not represent the evaporation of this ocean.
Astronomers re-examined Hubble observations from the last two decades to find this evidence of water vapor.

Further information in the press release to download