Atmosphere and ionosphere

Atmosphere and ionosphere - Galileo flybys[15 its high...

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Atmosphere and ionosphere Induced magnetic field around Callisto Callisto has a very tenuous atmosphere composed of carbon dioxide . [6] It was detected by the Galileo Near Infrared Mapping Spectrometer (NIMS) from its absorption feature near the wavelength 4.2 micrometers . The surface pressure is estimated to be 7.5 × 10 −12 bar (0.75 µPa ) and particle density 4 × 10 8 cm −3 . Because such a thin atmosphere would be lost in only about 4 days (see atmospheric escape ) , it must be constantly replenished, possibly by slow sublimation of carbon dioxide ice from the satellite's icy crust, [6] which would be compatible with the sublimation–degradation hypothesis for the formation of the surface knobs. Callisto's ionosphere was first detected during
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Unformatted text preview: Galileo flybys; [15] its high electron density of 7– 17 × 10 4 cm −3 cannot be explained by the photoionization of the atmospheric carbon dioxide alone. Hence, it is suspected that the atmosphere of Callisto is actually dominated by molecular oxygen (in amounts 10–100 times greater than CO 2 ). [7] However, oxygen has not yet been directly detected in the atmosphere of Callisto. Observations with the Hubble Space Telescope (HST) placed an upper limit on its possible concentration in the atmosphere, based on lack of detection, which is still compatible with the ionospheric measurements. [40] At the same time HST was able to detect condensed oxygen trapped on the surface of Callisto....
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