  Saturn's ionosphere is produced when the otherwise neutral atmosphere is
exposed to a flow of energetic charged particles or solar radiation. At low
latitudes the latter should result in a weak planet-wide glow in infrared (IR),
corresponding to the planet's uniform illumination by the Sun. The observed
low-latitude ionospheric electron density is lower and the temperature higher
than predicted by models. A planet-ring magnetic connection has been previously
suggested in which an influx of water from the rings could explain the lower
than expected electron densities in Saturn's atmosphere. Here we report the
detection of a pattern of features, extending across a broad latitude band from
~25 to 60 degrees, that is superposed on the lower latitude background glow,
with peaks in emission that map along the planet's magnetic field lines to gaps
in Saturn's rings. This pattern implies the transfer of charged water products
from the ring-plane to the ionosphere, revealing the influx on a global scale,
flooding between 30 to 43% of the planet's upper-atmospheric surface. This ring
`rain' plays a fundamental role in modulating ionospheric emissions and
suppressing electron densities.
