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Jupiter’s Dawn Storms are Remarkably Similar to Earth’s Auroral Substorms

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Dawn storms consist of short-lived but intense brightening and broadening of Jupiter’s main auroral oval near where the atmosphere emerges from darkness in the early morning region. Up to now, these immense displays of light had only been observed from ground-based and Earth-orbiting observatories, notably the NASA/ESA Hubble Space Telescope, only showing the Sun-facing side of the planet. New data from the Ultraviolet Spectrograph instrument on NASA’s Juno orbiter reveal for the first time where and how this phenomenon starts and its consequences.

“Observing Jupiter’s aurora from Earth does not allow you to see beyond the limb, into the nightside of Jupiter’s poles,” said lead author Dr. Bertrand Bonfond, a researcher at the University of Liège.

“Explorations by other spacecraft — Voyager, Galileo, and Cassini — happened from relatively large distances and did not fly over the poles, so they could not see the complete picture.”

“That’s why the Juno data is a real game changer, allowing us a better understanding what is happening on the nightside, where the dawn storms are born.”

During a dawn storm, Jupiter’s quiet and regular auroral arc transforms into a complex and intensely bright auroral feature.

It emits hundreds to thousands of Gigawatts of ultraviolet light into space as it rotates from the night side to the dawn side and ultimately to the day side of the planet over the course of 5-10 hours.

The jump in brightness implies that dawn storms are dumping at least 10 times more energy into Jupiter’s upper atmosphere than typical aurora.

“When we looked at the whole dawn storm sequence, we couldn’t help but notice that they are very similar to a type of terrestrial auroras called substorms,” said co-author Dr. Zhonghua Yao, also from the University of Liège.

Earth’s substorms result from brief disturbances in the planet’s magnetosphere that release energy high into the ionosphere.

The similarity between terrestrial and Jovian substorms is surprising because the magnetospheres of Jupiter and Earth are radically different.

On Earth, the magnetosphere is essentially controlled by the interaction of the solar wind with Earth’s magnetic field.

Jupiter’s magnetosphere is mostly populated by particles escaping from the volcanic moon Io, which then get ionized and trapped around the gas giant via its magnetic field.

“Even if their engine is different, showing for the first time the link between these two very different systems allows us to identify the universal phenomena from the peculiarities specific to each planet,” Dr. Bonfond said.

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