Saturn’s auroras may heat
its atmosphere like an electric toaster.
Measurements from NASA’s Cassini
spacecraft’s final orbits show that Saturn’s upper atmosphere is hottest where its auroras shine, a finding that could help solve a long-standing
mystery about the outer planets.
Saturn’s upper atmosphere is
much hotter than scientists first expected based on the planet’s distance from
the sun. In fact, all the gas giant planets — Saturn, Jupiter, Uranus and
Neptune — were thought to have chilly upper atmospheres of around 150 kelvins (–123° Celsius). But data from the Voyager spacecraft, which flew past the outer planets in the 1970s and 1980s (SN:
8/7/17), showed surprisingly toasty upper atmospheres of 400 to 600 kelvins
(125° to 325° C).
Planetary scientists dub this
mismatch an “energy crisis.” Something injects extra energy into the gas
giants’ atmospheres, but no one knew what. “Trying to explain why these
temperatures are so high has long been a goal in planetary atmospheric
physics,” says planetary scientist Ron Vervack of Johns Hopkins University’s
Applied Physics Laboratory.