A model for Io's atmosphere and sodium cloud

Abstract

view Abstract Citations (26) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A model for Io's atmosphere and sodium cloud. Macy, W., Jr. ; Trafton, L. Abstract Observations of the sodium D-line emissions associated with the Galilean satellite Io suggest that the emitting region has two components. The first is an atmosphere which extends 1000 km above Io's surface. This is a relatively dense region which is optically thick in the sodium D lines. The second component is a surrounding optically thin cloud spread out along Io's orbit to form part of a torus. No emission was detected during any of three eclipses observed, although Io's sodium emission was consistently present when Io was near orbital elongation. This indicates that resonant scattering is the principal emission mechanism in both components. For the atmosphere, measurements of the D-line intensity, D-2/D-1 ratio, and line width indicate a temperature of 500 to 1000 K and a sodium column abundance of 3 by 10 to the 13th power per sq cm. Upper limits to the abundance of Mg, K, Ca, and Li indicate a high sodium abundance ratio in the atmosphere. This may also be true for Io's surface if sputtering by energetic particles is the source of the atmosphere. The sodium cloud has been detected as far as 60 arcsec from Io in the orbital plane and at least 6 arcsec above and below this plane. The cloud can be sustained by atoms escaping from the critical level at the top of the atmosphere. Publication: The Astrophysical Journal Pub Date: September 1975 DOI: 10.1086/153817 Bibcode: 1975ApJ...200..510M Keywords: Astronomical Spectroscopy; Atmospheric Models; D Lines; Io; Planetary Atmospheres; Resonance Scattering; Abundance; Emission Spectra; Optical Thickness; Particle Flux Density; Pioneer 10 Space Probe; Sodium Vapor; Ultraviolet Spectra; Lunar and Planetary Exploration full text sources ADS |