This graphic illustrates the pointing and shows the data from one of many
observations made by the New Horizons Alice ultraviolet spectrometer (UVS)
instrument during the Pluto-bound spacecraft's recent encounter with
Jupiter. The red lines in the graphic show the scale, orientation, and
position of the combined "box and slot" field of view of the Alice UVS
during this observation.
The positions of Jupiter's volcanic moon, Io, the torus of ionized gas
from Io, and Jupiter are shown relative to the Alice field of view. Like a
prism, the spectrometer separates light from these targets into its
constituent wavelengths.
Io's volcanoes produce an extremely tenuous atmosphere made up primarily
of sulfur dioxide gas, which, in the harsh plasma environment at Io,
breaks down into its component sulfur and oxygen atoms. Alice observed the
auroral glow from these atoms in Io's atmosphere and their ionized
counterparts in the Io torus.
Io's dayside is deliberately overexposed to bring out faint details in the
plumes and on the moon's night side. The continuing eruption of the
volcano Tvashtar, at the 1 o'clock position, produces an enormous plume
roughly 330 kilometers (200 miles) high, which is illuminated both by
sunlight and "Jupiter light."
