Research Article

Far-Ultraviolet Imaging Spectroscopy of Io's Atmosphere with HST/STIS

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Science  15 Jan 1999:
Vol. 283, Issue 5400, pp. 353-357
DOI: 10.1126/science.283.5400.353

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Abstract

Well-resolved far-ultraviolet spectroscopic images of Oi, S i, and previously undetected H iLyman-α emission from Io were obtained with the Hubble space telescope imaging spectrograph (STIS). Detected O i and Si 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 ∼20 Io radii. All O i and Si features brightened by ∼50 percent in the last two images, concurrently with a ground-based observation of increased iogenic [O i] 6300-angstrom emission. The H iLyman-α emission, consisting of a small, ∼2-kilorayleigh patch near each pole, has a different morphology and time variation.

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