A Solution to Saturn’s Energy Crisis

Near-infrared composite image of Saturn captured by the Cassini spacecraft. The green regions are aurorae that are rich in hydrogen ions. Image credit: NASA/JPL/ASI/University of Arizona/University of Leicester

The gas giants of our solar system are so far from the Sun that they should have cold atmospheres. However, the upper atmosphere of Saturn (and the other gas giants) is, in fact, hundreds of degrees Celsius warmer than expected from solar heating alone, and the source of this additional heating has been debated. Data collected by the Cassini spacecraft reveal atmospheric aurorae similar to Earth’s northern and southern lights (aurora borealis and aurora australis). Scientists have previously suspected that ions and electrons spiraling in Saturn’s magnetic field induce electric currents in Saturn’s upper atmosphere creating the aurorae and preferentially heating Saturn’s poles, but suggested that energy would remain trapped where it was deposited. Research led by Zarah Brown at the University of Arizona observed stellar occultations in the extreme ultraviolet during the Cassini Grand Finale to create temperature and density maps with latitude and depth in the atmosphere. This study found that, while temperatures are highest near the auroral latitudes, winds and atmospheric waves inferred from these maps are able to redistribute that energy throughout the atmosphere to account for higher temperatures at all latitudes. These results provide fundamental knowledge of the physical processes operating in gas-giant atmospheres and are critical to planning future missions to the outer solar system and to studying exoplanets around other stars. READ MORE