Solar Winds Cause Shifts in Saturn's Radio Pulses

Scientists trying to measure Saturn's precise rotation rate have been experiencing difficulties in timing the radio pulses that the planet emits. Determining the precise rotation rate for planets with no solid surface like the gas giants has proven extremely difficult. The method they have been using consists of using the radio pulses emitted by the planet as a metronome, but new measurements suggest the method is not accurate since it can be disrupted by the solar winds.

Determining the precise rotation rate is a key component in the study of a planet, especially if it is not a rocky planet. By combining it with measurements of the gravitational field, information can be extracted about the size of the rocky core it may have and describe how gas giants like Saturn form.

In the 1980s, when NASA's Voyager spacecraft passed nearby the gas giants, it measured the regular radio pulses coming from Saturn every 10 hours and 39 minutes, a time close to the planet's rotation determined by observing the motions of the clouds and suggesting the radio pulse was directly connected to the rotation rate of the planet.

It is widely unknown what causes the radio pulse, one of the scenarios being that it is due to a "bump" in Saturn's magnetic field, carried by the planet as it rotates. Once a rotation, the bump meets a spot in Saturn's upper atmosphere where auroras are extremely active, giving off a burst of radio waves.

The spacecraft Cassini, recording the periodic pulses, discovered that they might vary by a few minutes in a mater of months or years, but this finding is highly controversial since a planet the size of Saturn cannot vary its spin rotation so fast, so scientists suggested that the radio pulses are not precisely tied to the rotation.

By studying the solar wind, they have found that the measured time between the radio pulses given off to the planet seems to increase when the solar winds reach slower speeds, and shortens at greater speed. So researchers have taken into consideration the fact that the intense aurora activity around Saturn's upper atmosphere spot is due to the solar winds; the changes in the timing of the collision with the magnetic field bump lead to time fluctuations in the period between the pulses.

By finding the correlation between the solar winds and the radio pulses emitted by Saturn, scientists are now able to measure with better accuracy the true rotation speed, although some still contest the fact that the radio periodicity is linked in any way to the planet's spin.