Discovered: Saturn’s rings are raining water
Cosmic rain! Astronomers have discovered that the rings
of Saturn produce their own rain that falls onto the planet, having a
major impact on its atmosphere.
A new study tracked
the “rain” of charged water particles into the atmosphere of Saturn and
found there is more of it and it falls across larger areas of the planet
than previously thought.
The study, whose
observations were funded by NASA and whose analysis was led by the
University of Leicester, England, reveals that the rain influences the
composition and temperature structure of parts of Saturn’s upper
atmosphere.
“Saturn is the first planet to show
significant interaction between its atmosphere and ring system,” said
James O’Donoghue, lead author of the study.
“The main
effect of ring rain is that it acts to ‘quench’ the ionosphere of
Saturn. In other words, this rain severely reduces the electron
densities in regions in which it falls,” he said in a NASA statement.
O’Donoghue
noted the ring’s effect on electron densities is important because it
explains why, for many decades, observations have shown those densities
to be unusually low at certain latitudes on Saturn.
The
study, published in the journal Nature, also helps scientists better
understand the origin and evolution of Saturn’s ring system and changes
in the planet’s atmosphere.
“It turns out that a
major driver of Saturn’s ionospheric environment and climate across vast
reaches of the planet are ring particles located some 60,000 kilometres
overhead,” said Kevin Baines, a co-author of the study.
“The
ring particles affect both what species of particles are in this part
of the atmosphere and where it is warm or cool,” Baines said.
In
the early 1980s, images from NASA’s Voyager spacecraft showed two to
three dark bands on Saturn, and scientists theorised that water could
have been showering down into those bands from the rings.
Those
bands were not seen again until this team observed the planet in
near-infrared wavelengths with the W M Keck Observatory on Mauna Kea, in
Hawaii.
The ring rain’s effect occurs in Saturn’s
ionosphere, where charged particles are produced when the otherwise
neutral atmosphere is exposed to a flow of energetic particles or solar
radiation.
Both Earth and Jupiter have an equatorial
region that glows very uniformly. Scientists expected this pattern at
Saturn, too, but they instead saw dramatic differences at different
latitudes.
“Where Jupiter is glowing evenly across
its equatorial regions, Saturn has dark bands where the water is falling
in, darkening the ionosphere,” said Tom Stallard, co-author of the
study.
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