For the First Time, the Birth of Jupiter's Enigmatic Auroral Storms Has Been Observed

 

(ESA/Hubble & NASA/ULiège/Bonfond)

Earth's auroras are impressive, but other planets in the Solar System have their own variations of the atmospheric light display.

Jupiter, in fact, has the strongest auroras in the Solar System, which shine brightly in ultraviolet wavelengths but are invisible to our eyes.

Since Jupiter is so dissimilar to Earth, scientists are particularly interested in figuring out what causes these amazing atmospheric phenomena - and they've recently discovered a new clue. We've seen the start of Jupiter's enigmatic auroral dawn storm for the first time, thanks to the Juno orbiter.

The auroras on Jupiter are caused by a steady rain of high-energy electrons that are largely stripped from Io's atmosphere. These are accelerated to Jupiter's poles along magnetic field lines, where they crash into the upper atmosphere and interact with the gases to create a glow.

The auroras on Earth, on the other hand, are caused by particles in the solar wind. Jupiter's auroras, unlike those on Earth, are permanent and can behave in a variety of ways.

The dawn storm, a brightening and broadening of the aurora at dawn that was first observed in 1994, is one of these habits. These dawn storms, on the other hand, begin on the night side of the pole, and we hadn't been able to see them shape until NASA's Juno probe arrived.

According to astronomer Bertrand Bonfond of the University of Liège in Belgium, viewing Jupiter's aurora from Earth does not allow you to see beyond the limb, into the night side of Jupiter's poles.

Other spacecraft's explorations occurred over relatively long distances and did not travel over the poles, so they were unable to see the whole image. That's why the Juno data is such a game-changer, helping us to gain a better understanding of what's going on on the night side, where the dawn storms start.

The emergence of a dawn storm. (NASA/JPL-Caltech/SwRI/UVS/ULiège/Bonfond)

Dawn storms are a sight to behold. They begin on Jupiter's night side and rotate into view as dawn breaks, transforming the planet's aurora into a dazzling ultraviolet beacon that emits hundreds to thousands of gigawatts of light - at least ten times the energy of the typical Jovian aurora. They last for a few hours before returning to more natural levels of energy.

Since the auroras on the two planets are so dissimilar, the mechanism that triggers the dawn storm was supposed to be unlike anything seen in Earth's auroras. The data from Juno's ultraviolet spectrograph, on the other hand, appeared strangely familiar.

We couldn't help but note that the dawn storm auroras on Jupiter are very similar to a sort of terrestrial aurora called sub storms when we looked at the entire dawn storm series, said astronomer Zhonghua Yao of the University of Liège.

The auroral substorms that occur on Earth are breathtaking to watch. Electric currents disrupt the Earth's magnetosphere, resulting in an intense release of energy into the ionosphere. The energy is dissipated in the form of a dynamic, dancing aurora that can last for many hours.

The solar wind and the direction of the interplanetary magnetic field have a major effect on sub storms. However, encounters with the solar wind dominate Earth's magnetosphere; Jupiter's is packed with plasma stripped from Io, which is dominated by the planet's position.

Jupiter's auroral dawn storms are influenced by an over-spill of plasma from Io, rather than the solar wind, according to the team's analysis.

In both cases, a build-up of plasma and energy causes the system to become increasingly unstable, eventually resulting in an auroral storm.

This can only help us better understand auroral processes on both planets, as well as aurora on other bodies in the future, such as brown dwarfs, which have large enough auroras to be detected through interstellar space and though they are not near a star.

Although the 'engines' of the auroras on Earth and Jupiter are very different, showing the similarities between the two systems for the first time helps us to recognise universal phenomena and distinguish them from planet-specific peculiarities, according to Yao.

The Earth's and Jupiter's magnetospheres store energy in very different ways, but when this accumulation reaches a breaking point, the two systems unleash it explosively in a surprisingly similar way.

The research has been published in AGU Advances.