Galileo Imaging of Atmospheric Emissions from Io
P. E. Geissler,
1*
A. S. McEwen,
1
W. Ip,
2
M. J. S. Belton,
3
T. V. Johnson,
4
W. H. Smyth,
5
A. P. Ingersoll
6
The Galileo spacecraft has detected diffuse optical
emissions from Io in high-resolution images acquired while the
satellite was eclipsed by Jupiter. Three distinct components make up
Io's visible emissions. Bright blue glows of more than 300 kilorayleighs emanate from volcanic plumes, probably due to electron
impact on molecular sulfur dioxide. Weaker red emissions, possibly due to atomic oxygen, are seen along the limbs, brighter on the pole closest to the plasma torus. A faint green glow appears concentrated on
the night side of Io, possibly produced by atomic sodium. Io's disk-averaged emission diminishes with time after entering eclipse, whereas the localized blue glows brighten instead.
1 Lunar and Planetary Laboratory, University of
Arizona, Tucson, AZ 85711, USA.
2 Institute of
Astronomy, National Central University, Chung-Li, Taiwan 320, Republic
of China.
3 National Optical Astronomy
Observatories, Tucson, AZ 85719, USA.
4 Jet
Propulsion Laboratory, MS 23-201B, 4800 Oak Grove Drive, Pasadena, CA
91109, USA.
5 Atmospheric and Environmental
Research, 840 Memorial Drive, Cambridge, MA 02139, USA.
6 Division of Geology and Planetary Sciences,
California Institute of Technology, Pasadena, CA 91125, USA.
*
To whom correspondence should be addressed. E-mail:
geissler{at}lpl.arizona.edu
