How long is a day on Saturn?

  • Saturn’s northern and southern lights found to pulse
  • Pulsation pattern is same as radio emission from Saturn
  • Gives hints as to the planet’s so-far uncertain day length

A team of scientists led by Dr Jonathan Nichols of the University of Leicester has found that Saturn’s aurora—an ethereal ultraviolet glow near the planet’s poles (see video above)—pulses roughly once per Saturnian day.

The length of Saturn’s day has been under much discussion since it was discovered that the traditional ‘clock’ used to measure the planet’s rotation period, apparently does not keep good time.

Like all magnetised planets, Saturn—a gas giant with no visible solid surface for reference—emits radio waves into space from its polar regions. These radio emissions pulse with a period near to 11 hours, and the timing of the pulses was originally thought to represent the rotation of the planet.

However, over the years the period of the pulsing has varied. Since the rotation of a planet cannot be easily sped up or slowed down, the hunt for the source of the varying radio period has become one of the most perplexing puzzles in planetary science.

Now, in a paper published in the journal Geophysical Research Letters, Nichols and colleagues have used images from the Hubble Space Telescope of Saturn’s aurorae to show that, not only do the radio emissions pulse, but the aurorae vary in time with the radio.

Aurorae, more commonly known as the “northern lights” or “southern lights” on Earth, are caused when charged particles in space are funnelled along a planet’s magnetic field and into the planet’s upper atmosphere near the poles, whereupon they hit gas particles and cause them to glow.

Saturn’s radio waves were long-suspected to be emitted by the charged particles as they hurtle toward the poles, but no pulsing had been observed in the aurora…a puzzling difference between two supposedly related phenomena.

However, the team found that by using the radio pulsing to organise the auroral data, and stacking all the Hubble Saturn images from 2005-2009 on top of each other, the auroral pulsing finally revealed itself.

“This confirms that the auroras and the radio emissions are indeed physically associated, as suspected,” adds Dr Nichols.

But does this research finally answer the question of the length of the Saturnian day?

The answer is no, it doesn’t quite. But it does help feed into the best current estimate: 10 hours, 32 minutes and 35 seconds.

And here’s a NASA/JPL video clip with space scientist Andy Ingersoll, who discusses the causes and effects of the aurora on Saturn:

Adapted from information issued by Jonathan Nichols / University of Leicester NASA / ESA / J. Clarke (Boston University) / Z. Levay (STScI).

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