Somewhere deep below Saturns cloud tops, the planet rotates at a constant speed. Determining this interior period of rotation has proven extremely complicated. Now, with new Cassini results, a team of European scientists have taken an important step forward.
The results, published in Nature, are based on data from the Radio and Plasma Wave Science instrument on Cassini. Determining the length of a day on one of the gas giant planets, has been difficult. The interior of the planet is masked completely by the clouds in the upper atmosphere. So to measure the internal rotation of the planet, scientists need a property that is associated with the interior and yet is observable from space. It proves to be radio emission. Electrically charged particles trapped in the planets magnetic field release radio waves with frequencies around 100 kilo Hertz. The magnetic field itself is generated deep inside the planet, so watching the variation of the radio emission as the magnetic field sweeps around can reveal the planets rotation rate.
Two researchers have published their recent findings in the July 23 issue of the Geophysical Research Letters. Their paper is based on data from the Cassini spacecraft radio and plasma wave science instrument. Their study investigates sounds that are not just eerie, but also descriptive of a phenomenon similar to Earth's northern lights.
"All of the structures we observe in Saturn's radio spectrum are giving us clues about what might be going on in the source of the radio emissions above Saturn's auroras. We believe that the changing frequencies are related to tiny radio sources moving up and down along Saturn's magnetic field lines" - Dr. Bill Kurth, deputy principal investigator for the instrument. He is with the University of Iowa, Iowa City. Kurth made the discovery along with Principal Investigator Don Gurnett, a professor at the University.