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Spotlight on Jupiter’s aurorae
7/7/15

The solar wind is ruled out

Up to now, the origin of aurorae located at the exterior of the principal oval was unknown. “We had already observed variations in their brightness and I put forward the theory of an internal origin, that is to say, an intensification of the volcanic activity of Io, which increased the quantity of gas emitted”, recalls Bertrand Bonfond. “This was bound to create more events involving the redistribution of plasma in the Jovian system but this was only one interpretation. We lacked the data which made it possible to verify this theory”. During the two weeks of observation at the beginning of 2014, Earth and Jupiter were aligned in relation to the sun. This was the optimal situation for extrapolating the intensity of the solar wind on Jupiter according to its characteristics as seen from Earth. “For an entire week, the solar wind was very constant on Earth. This was a Godsend. While the variations are difficult to extrapolate with precision we can conclude that if nothing occurred on Earth then nothing occurred on Jupiter either. ” During this period, the researchers located peaks of brightness which were as intense as they were sudden. “ We therefore concluded from this that the solar wind had nothing to do with these auroral intensifications. The process involved was internally driven. In-depth analyses enabled us to confirm that there was a redistribution of plasma.

variations solar winds Jupiter

The next few years look promising

If analyses of repeated images and the considerable improvement of observation tools have made it possible to understand the previously unpublished physical processes on Earth, there are still a lot of grey areas in relation to Jupiter. “For example, for the events linked to the solar wind, we know that it has a role to play, notably by the compression and release of Jupiter’s magnetosphere. At the same time, the Jovian system is enormous. On Earth, everything happens very quickly. On Jupiter, we do not know the response time of the system in relation to the influence of the solar wind. In theory, the brightness of the principal oval should diminish when the solar wind intensifies. And yet what we observe is the opposite. We think that the chronological order of the different events when the solar wind is enhanced is crucial. Unfortunately, it is exactly this precise timing which eludes us for the moment”, explains Bertrand Bonfond.

Always on the lookout for discoveries and new analyses, the astrophysicist impatiently awaits the year 2016 and the arrival of the space probe Juno around Jupiter. “Juno possesses a magnetometer and will be capable of observing the variations in the solar wind in real time. We have requested more time on the Hubble telescope. We do not yet know if this will be accepted. But for the first time, we will be capable of observing the aurorae of Jupiter while taking account of the solar wind. Observing what happened when the solar wind was stable was one thing. The next stage will be to observe what happens when its speed and pressure vary in a known way”.

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