Far-ultraviolet imaging spectroscopy of Io's atmosphere with HST/STIS.
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Well-resolved far-ultraviolet spectroscopic images of O I, S I, and previously undetected H ILyman-alpha emission from Io were obtained with the Hubble space telescope imaging spectrograph (STIS). Detected O I and S I lines (1250 to 1500 angstroms) have bright equatorial spots (up to 2.5 kilorayleighs) that shift position with jovian magnetic field orientation; limb glow that is brighter on the hemisphere facing the jovian magnetic equator; and faint diffuse emission extending to approximately 20 Io radii. All O I and S I features brightened by approximately 50 percent in the last two images, concurrently with a ground-based observation of increased iogenic [O I] 6300-angstrom emission. The H ILyman-alpha emission, consisting of a small, approximately 2-kilorayleigh patch near each pole, has a different morphology and time variation. (+info)
A tenuous carbon dioxide atmosphere on Jupiter's moon Callisto.
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An off-limb scan of Callisto was conducted by the Galileo near-infrared mapping spectrometer to search for a carbon dioxide atmosphere. Airglow in the carbon dioxide nu3 band was observed up to 100 kilometers above the surface and indicates the presence of a tenuous carbon dioxide atmosphere with surface pressure of 7.5 x 10(-12) bar and a temperature of about 150 kelvin, close to the surface temperature. A lifetime on the order of 4 years is suggested, based on photoionization and magnetospheric sweeping. Either the atmosphere is transient and was formed recently or some process is currently supplying carbon dioxide to the atmosphere. (+info)