Ringing rings reveal Saturn’s innards

Vibrations induced by planet send signals about interior’s structure


RINGED GIANT  Saturn’s rings cast a shadow on the planet in a 2012 Cassini spacecraft photo. Subtle vibrations in those rings are helping scientists explore the structure of the gas giant’s interior.

NASA/JPL-Caltech/Space Science Institute

BALTIMORE — Saturn is surrounded by a vast seismometer: its rings. Recently detected ripples in the gas giant’s rings carry signatures of the planet’s interior structure, offering new insights into what lies far beneath Saturn’s cloud tops. “It’s the first useful seismology on another planet,” says Jim Fuller, a theoretical astrophysicist at Caltech. His research, presented April 11 at a meeting of the American Physical Society, could help scientists understand the formation of planets within and outside the solar system.

Saturn ring seismology began in 2013, when scientists discovered that the periodic rise and fall of the planet’s surface produces gravitational fluctuations that show up as vibrations in the rings. Just as seismic waves produced by earthquakes encode information about Earth’s interior, Saturn’s ring vibrations betray what’s lurking inside the planet.

RUSTLING RINGS Saturn’s seismic vibrations manifest themselves as waves coursing through particles in the planet’s rings. Jim Fuller

Fuller says the wave patterns indicate that Saturn’s interior is more intricate than a solid core surrounded by churning layers of gas. He proposed in a recent paper that Saturn’s deep interior has a stable layer of fluid, perhaps in the form of highly pressurized liquid helium. He is also exploring whether the core could be gradually dissolving into the surrounding fluid. By comparing seismic data with magnetic field measurements, Fuller is devising a more detailed structural profile. The Cassini spacecraft may provide more precise gravitational measurements in the months before its lethal descent into Saturn in 2017.

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