Hubble Space Telescope detects thin oxygen atmosphere on Ganymede
Jupiter`s largest moon, Ganymede, may have a tenuous oxygen atmosphere. Researchers from the Space Telescope Science Institute and Johns Hopkins University (both Baltimore, MD) drew this conclusion based on ultraviolet data from the Hubble Space Telescope`s Goddard High-Resolution Spectrograph. The moon`s atmosphere has a pressure equal to 10-11 that at the Earth`s surface, roughly equivalent to the pressure of the Earth`s atmosphere 200 nautical miles above the surface. The investigators note that unlike the oxygen in the Earth`s atmosphere, which is thought to have arisen from life functions, that above Ganymede probably stems from sublimation of oxygen atoms from water molecules frozen on the moon`s surface and exposed to sunlight.
The spectrograph indicated two oxygen peaks attributed to light emitted from both the north and south poles of the satellite. Team leader Doyle Hall notes this is "very tentative evidence for the existence of polar aurorae" from the interaction of charged particles colliding with the atmosphere. Aurorae have been seen on Jupiter, as well as Earth, but never in the atmosphere of any moon. The Jovian moon Europa, with a largely frozen surface and perhaps subterranean oceans, also has a weak oxygen atmosphere.