Seeing Ice. . . Sublimate. . . Directly To Water Vapor. Poetry Happens -- On The Solar System's Largest Moon. . .

The Jovian moon Ganymede (as captured by Juno, at close range, below -- and by Hubble, at right) is larger than the planet Mercury. And it is generally very cold -- like minus 300 degrees on the night side. But at midday, as our Sun bombards it with charged particles, near the equator, the rock hard ice sublimates -- that is, it transfers directly from solid. . . to an ether -- a gas. And in doing so, it releases a significant amount of molecular oxygen, into the very thin atmosphere of that moon.

This is the heretofore unknown discovery published this week, primarily by using archival Hubble imagery and data. Here is the story:

. . .Roth and his team then took a closer look at the relative distribution of the aurora in the UV images. Ganymede’s surface temperature varies strongly throughout the day, and around noon near the equator it may become sufficiently warm that the ice surface releases (or sublimates) some small amounts of water molecules. In fact, the perceived differences in the UV images are directly correlated with where water would be expected in the moon’s atmosphere.

“So far only the molecular oxygen had been observed,” explained Roth. “This is produced when charged particles erode the ice surface. The water vapor that we measured now originates from ice sublimation caused by the thermal escape of water vapor from warm icy regions.”

This finding adds anticipation to ESA (European Space Agency)’s upcoming mission, JUICE, which stands for JUpiter ICy moons Explorer. JUICE is the first large-class mission in ESA’s Cosmic Vision 2015-2025 program. Planned for launch in 2022 and arrival at Jupiter in 2029, it will spend at least three years making detailed observations of Jupiter and three of its largest moons, with particular emphasis on Ganymede as a planetary body and potential habitat. . . .

As ever, we are grinning -- at the idea of a decidedly warm -- almost steamy -- mist, rising slowly but directly (never becoming a wet, liquid sweat), off the center of this lithe body. . . at midday. It is almost like late summer -- at the state park. Almost. Grin.



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