Jupiter’s Spectacular Ultraviolet “Dawn Storm” Auroras Are Surprisingly Earth-Like

Even if Jupiter’s diameter is ten times that of Earth, this illustration shows the similarities between the two types of aurora. Photo credit: NASA / JPL-Caltech / SwRI / UVS / STScI / MODIS / WIC / BILD / ULiège / Bonfond

A new study tracks the life cycle of the spectacular ultraviolet storms in the great planet’s aurora, generated by charged particles from its volcanic moon Io.

The storms, which are the lightening and widening of the morning flank of an oval of auroral activity that surrounds them JupiterThe poles develop in a pattern that is surprisingly reminiscent of familiar waves in the aurora, which, according to the authors, move in waves across the Earth’s polar sky and are known as auroral sub-storms.

The new study is the first to track the storms from their birth on the giant planet’s night side throughout their evolution. It was published on March 16, 2021 in AGU Advances, the AGU journal for meaningful, short-format reports with an immediate impact on all earth and space sciences.

During a morning storm, Jupiter’s calm and regular auroral arc transforms into a complex and intensely bright auroral feature. It emits hundreds of thousands of gigawatts of ultraviolet light into space as it spins from the night side to the dusk side and eventually the day side of the planet in 5 to 10 hours. One gigawatt is the electricity that is generated by a typical modern nuclear reactor. This colossal brightness implies that at least ten times more energy has been transferred from the magnetosphere to Jupiter’s upper atmosphere.

Development of a dawn storm in Jupiter's polar aurora

These observations are from the Juno Ultraviolet Spectrograph (UVS) instrument. Photo credit: NASA / JPL-Caltech / SwRI / UVS / ULiège / Bonfond

So far, morning storms have only been observed by ground-based telescopes on Earth or on Earth Hubble Space Telescopethat can only offer side views of the aurora and cannot see the night side of the planet. Juno rotates around Jupiter every 53 days along a greatly elongated orbit that takes him directly over the poles in each orbit.

“This is a real game changer,” said Bertrand Bonfond, researcher at the University of Liège and lead author of the new study. “We finally have to find out what happened on the night side, where the morning storms are born.”

Well-known auroral sequences, different motors Polar aurors on Earth and on Jupiter are images of processes that take place in the magnetic fields surrounding them. Both planets create magnetic fields that trap charged particles.

A study carried out by researchers from the Laboratory of Planetary and Atmospheric Physics at the University of Liège shows, for the first time, global views of a morning storm, a spectacular auroral phenomenon that occurs on Jupiter. Photo credit: University of Liège

The earth’s magnetosphere is formed by charged particles flowing out of the sun, known as the solar wind. Solar gusts expand the Earth’s magnetic field into a long tail on the night side of the planet. When this tail snaps back, it fires charged particles into the nightly ionosphere, which appear as spectacular auroral light shows.

The new study found that the timing of the morning storms on Jupiter did not correlate with the fluctuations in the solar wind. Jupiter’s magnetosphere is mainly populated by particles that escape from its volcanic moon Io and are then ionized by its magnetic field and trapped around the planet.

The sources of mass and energy differ fundamentally between these two magnetospheres, resulting in aurors that usually look very different. However, the dawn storms, deciphered by Junos UV spectrographs, looked familiar to the researchers.

“When we looked at the entire sequence of morning storms, we couldn’t help but notice that the morning storm aurors at Jupiter are very similar to a type of terrestrial auror called substorms,” ​​said Zhonghua Yao, co-author of the study and research assistant at the University of Liège.

The partial storms result from the explosive reconfiguration of the tail of the magnetosphere. On Earth, they are closely related to the variations in the solar wind and the orientation of the interplanetary magnetic field. On Jupiter, such explosive reconfigurations are more likely to have an overflow of the plasma coming from Io.

These results show that particles and energy, regardless of their source, do not always circulate smoothly in planetary magnetospheres. They often accumulate until the magnetospheres collapse and create substorm-like reactions in the planetary aurors.

“Even if their engine is different, by showing the connection between these two very different systems for the first time, we can identify the universal phenomena based on the specifics specific to each planet,” said Bonfond.

Read the dark origins of one of Jupiter’s great light shows unveiled by NASA’s Juno spacecraft to learn more about this research.

Reference: “Are Dawn Storms Jupiter’s Auroral Substorms?” by B. Bonfond, ZH Yao, GR Gladstone, D. Grodent, J.-C. Gérard, J. Matar, B. Palmaerts, TK Greathouse, V. Hue, MH Versteeg, JA Kammer, RS Giles, C. Tao, MF Vogt, A. Mura, A. Adriani, BH Mauk, WS Kurth and SJ Bolton, March 16, 2021, AGU advances.
DOI: 10.1029 / 2020AV000275

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