How Jupiter powers its aurora

12 September 2017

Interview with

Barry Mauk, Johns Hopkins University

The Northern Lights - also known as the Aurora Borealis, are a beautiful display of dancing lights in the night sky, but aurorae are not just Earthly phenomena. Similar light shows have been spotted on Saturn, Uranus, Neptune and Jupiter and the question is are these manifestations created in the same way as they are here on Earth? A new paper out in Nature has revealed what powers the Jupiter aurorae, thanks to some very high tech instruments aboard the Juno spacecraft.  Barry Mauk, from Johns Hopkins University, is one of the lead investigators on the project and he spoke to Georgia Mills…

Barry - The Northern Lights are an image - a TV image if you will - of this processes that are going on in Earth’s space environment - it’s called a magnetosphere. Basically, the solar wind, the wind of ionised gases that come from the Sun blow over Earth’s magnetic field. It acts as a giant electrical generator that drive electric currents within Earth’s magnetosphere. Those electric currents, some of them flow along the magnetic fields towards the polar magnetosphere and they encounter resistances to that current flow. Whenever a current encounters a resistance, you build up an electrical potential, and it’s that electrical potential that then accelerates electrons down onto Earth’s atmosphere that generates these dramatic lights.

We see this phenomena at Earth, Jupiter, Saturn, Uranus, and Neptune so far. I’ve described to you one process that generates aurorae on Earth, there are several other processes that can also generate aurorae on Earth. For these other planets, we don’t quite know which of the processes are involved in generating the aurorae. We can guess that they’re generated by similar processes, but we do not know for sure.

Georgia - You were interested in the aurorae on Jupiter. What did you want to find out and how did you go about investigating?

Barry - The Juno mission has multiple science goals. One of the major science goals is to understand Jupiter’s polar space environment, and particularly to understand Jupiter’s aurorae. So we went to Jupiter and we built instruments; there are maybe five instruments on Juno that are directed towards understanding Jupiter’s aurorae.

The instrument that I’m the lead investigator for is the Jupiter Energetic Particle Detector Instrument, which we call JEDI for short, and it is the one that was able to see this specific phenomena that we report in our recent paper.

Georgia - JEDI, so it was detecting the force I suppose?

Barry - Something like that, yes.

Georgia - What did JEDI find then? How was Jupiter’s aurorae created, is it the same way as on Earth?

Barry - We see some similar features. What we are reporting in this recent paper is the observations; we saw what we call these inverted V structures. What these inverted V’s indicate when we fly over an auroral form is that there are large electrical potentials that are along the magnetic field lines that are accelerating electrons down onto Jupiter’s atmosphere and are helping to create the aurorae.

Georgia - So you found these incredibly high electric potentials. Much higher than Earth, but it is a similar process?

Barry - At Earth the potentials are much lower; they are typically several thousand volts. The other major difference between Earth and Jupiter is that the power source is different. We talked about the solar wind blows over the magnetic field of Earth and acts as an electrical generator - that’s the power source. At Jupiter, the power source is Jupiter’s rotation. The rotation of Jupiter within it’s own large magnetic field acts as an electrical generator, and it is that process that generates the electrical currents.

Georgia - Why have you done this? Why is it important to know about the aurorae on Jupiter?

Barry - Our research is curiosity driven. We are trying to understand what processes operate in the universe and so it is curiosity driven. There are practical implications. One of things that we are finding is that the auroral processes are energising electrons to immense energies, to much higher energies that we see at Earth. These high energy electrons have energies comparable to the energies of Jupiter’s radiation belt. So, on that basis, we’re trying to understand how Jupiter’s radiation belt is created so that we can better engineer future missions to Jupiter, because high radiation is such an engineering technical challenge to missions that go to Jupiter.

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