A series of photos from the Hubble Space Telescope show the dancing light of Saturn's auroras, a unique phenomenon within our solar system.
Credit: NASA/ESA/J. Clarke
ASHLAND: Saturn’s luminous auroras appear to be pulsing, and their ultraviolet glow waxes and wanes in connection with the planet’s puzzling radio emissions, scientists have discovered.
The source of these mysterious emissions has stymied researchers for many years, and this finding puts them one step closer to finding the missing link between the radio and auroral emissions, said lead author Jonathan Nichols, an astronomer at the University of Leicester, U.K..
“The hunt for this process is presently underway,” said Nichols. “We have now shown that the auroras also pulse in time with the radio emissions… This finding is therefore a 'signpost' telling us that by studying the electric currents flowing in Saturn's magnetosphere we may discover the mystery cause of the varying radio period.”
Pulsing not caused by Saturn’s rotations
Magnetised planets, like Saturn, emit radio waves that can be measured. Researchers originally thought that the pulses correspond with the rotation of the planet, but upon closer observation from the Voyager satellite missions, they realised that the pulsing varied widely.
This irregularity was difficult to explain, given that the rotation of a massive planet like Saturn cannot easily speed up or slow down.
Now, Nichols and his team are using images taken from the NASA/ESA Hubble Space Telescope of Saturn’s auroras, stacking the results on top of each other to reveal how the pulsing occurs concurrently with the radio emissions, their results to be published in Geophysical Research Letters.
Magnetic fields indicate rotation rate
Auroras, also known as “northern lights”, are curtains of charged particles that dance along a planet’s magnetic field and bump into the atmosphere, making them glow. Particles from the Sun or nearby moons can make auroras more prevalent and noticeable.
The rotation rates of terrestrial planets such as Earth are well known because they have solid surfaces on which there are fixed landmarks that can be tracked, Nichols said.
Gaseous planets, on the other hand, are not the same. “Saturn, like other gas giants, presents no such solid surface, so by the term ‘rotation rate’ scientists really mean the rotation rate of the deep interior of the planet,” Nichols said.
“This is where planetary magnetic fields come in handy, since they are thought to be generated deep within the planetary interior, such that the rotation rate of the magnetic field is a good indicator of the rotation rate of the planet.”
Confirming the aurora-pulse connection
The team’s findings confirm a physical connection between Saturn’s auroras and the planet’s radio emissions, said Nichols, and that the radio pulses are being loosely influenced by its planetary rotation period. However, the way they are being altered is as-yet unknown.
“Their research is really exciting and apparently resolves a long-standing problem in the auroral research of Saturn,” said Mary Mlynczak, geophysicist at NASA’s Langley Research Centre.
