Alternating currents cause the dawn of Jupiter

An international team of researchers has successfully measured the current system responsible for the aurora of Jupiter. Using the data transmitted to the Earth by NASA's Juno probe, they showed that the direct currents were much lower than expected and that the alternating currents therefore had to play a special role. On Earth, however, a DC system creates its auroras. The Jupiter electrical current system is maintained, in particular by large centrifugal forces, which project ionized sulfur dioxide from the moon of the gas giant Io through the magnetosphere.

Professor Joachim Saur of the Institute of Geophysics and Meteorology of the University of Cologne participated in the project. The article "The Birkeland currents in the magnetosphere of Jupiter observed by the Juno satellite in polar orbit" is published in the latest issue of Nature Astronomy.

Jupiter, the largest planet in the solar system, has the brightest dawn, with a radiant power of 100 terawatts (100,000,000,000 kilowatts = one hundred billion KW). 100,000 power stations would be needed to produce this light. In the same way as on Earth, the aurorae of Jupiter appear as two huge oval rings around the poles. They are powered by a gigantic system of electric currents that connects the polar light region to the magnetosphere of Jupiter. The magnetosphere is the region around a planet that is influenced by its magnetic field. Most electric currents flow along Jupiter's magnetic field lines, also known as Birkeland currents.

NASA's Juno spacecraft has been in polar orbit around Jupiter since July 2016. Its goal is to better understand the interior and aurora of Jupiter. Juno measured for the first time the continuous electric current system responsible for the aurora of Jupiter. To this end, scientists measured the environment of Jupiter's magnetic field with great precision in order to deduce the electric currents. The total current is about 50 million amps. However, this value is clearly lower than the theoretically expected values. The reason for this discrepancy is due to small-scale turbulent alternative currents (also called alfvenic currents), which have so far received little attention. "These observations, combined with other measurements from the Juno spacecraft, show that alternative currents play a much larger role in generating Jupiter's aurora than the DC system." said Joachim Saur. He has been researching these turbulent alternative currents for 15 years, emphasizing their importance. The aurorae of Jupiter differ from those of the Earth, which are essentially generated by direct currents. The northern lights of the Earth shine about a thousand times weaker, because the Earth is smaller than Jupiter, its magnetic field is weaker and its rotation is slower.

"Jupiter's electrical power systems are powered by the enormous centrifugal forces of Jupiter's rapidly rotating magnetosphere," Saur said. The volcanically active Jupiter Moon produces one tonne of sulfur dioxide per second, which ionizes in the magnetosphere of Jupiter. "Because of the fast rotation of Jupiter (a day on Jupiter lasts only ten hours), the centrifugal forces move the ionized gas into the magnetic field of Jupiter, which generates the electric currents," concludes the geophysicist.