Solar system planets have their own version of the atmospheric light show, just as Earth has astonishing aurora.
Jupiter has the strongest auroras in the solar system – invisible to our eyes, but glowing brilliantly at ultraviolet wavelengths.
And because Jupiter is so different from Earth, scientists have invested deeply in figuring out what drives these amazing weather phenomena – and they just got new evidence. Thanks to the “Juno” orbiter, they have now observed for the first time the beginning of the mysterious twilight storm of Jupiter.
The auroras of Jupiter are produced by continuous rain of high-energy electrons, stripped from Io’s atmosphere. It is accelerated along magnetic field lines to the poles of Jupiter, where it falls into the upper atmosphere and interacts with gases to produce a glow.
(ESA / Hubble & NASA / ULiège / Bonfond)
This is in contrast to auroras, which are produced by particles from the solar wind. Also unlike the aurora borealis, Jupiter’s aurora is permanent and can behave completely differently. One of these behaviors is the dawn storm – the intense brightness and widening of the aurora borealis at dawn, first observed in 1994. However, these dawn storms start on the night side of the pole, and we could never see them forming until NASA’s Juno probe reached The scene of the accident.
(NASA / JPL-Caltech / SwRI / UVS / ULiège / Bonfond)
“Observing Jupiter’s auroras from Earth does not allow you to see beyond the tip, on the night side of Jupiter’s poles,” said astronomer Bertrand Bonfond, from Liège University in Belgium, that the explorations by other spacecraft have occurred from relatively large distances. “It did not fly over the poles, so you couldn’t see the full picture. That is why Juno data is a real game changer, which gives us a better understanding of what happens at night when dawn storms generate.”
Dawn storms begin on the night side of the planet and rotate in vision as dawn breaks, and the aurora turns to Jupiter into a glowing ultraviolet beacon, giving hundreds to thousands of gigawatts of light – at least 10 times the energy of the usual Jovian aurora. It lasts for a few hours before dipping to more normal energy levels.
Because the planets have such differences between the aurora borealis, the process that generates the dawn storm was expected to be different from any processes seen in the auroras on Earth. But surprisingly, the data from the Juno ultraviolet spectroscope seemed strangely familiar.
“When we looked at the entire Dawn storm sequence, we couldn’t help but notice that the aurora borealis of the dawn storm on Jupiter is very similar to a kind of terrestrial aurora called sub-storms,” said astronomer Zhonghua Yao of Liège University.
It’s amazing to see aurora storms on Earth. They occur when electric currents in the Earth’s magnetosphere are disturbed, causing an explosive release of energy into the ionosphere. There, energy is dissipated in an intricate dancing aurora that can last for several hours.
Substorms are strongly influenced by the solar winds and the direction of the interplanetary magnetic field. But the Earth’s magnetosphere is dominated by interactions with the solar wind. Jupiter is also full of Io-stripped plasma, which is controlled by the planet’s position.
According to the team’s analysis, Jupiter’s twilight storms are affected by excessive plasma spills from Io, rather than the solar wind. But the result is the same, a disturbance in the magnetosphere that leads to an explosive release of energy.
Either way, the accumulation of plasma and energy gradually increases instability in the system until boom – the auroral storm.
This could only increase our understanding of auroral processes on all planets, and it could help us better understand auroras on other bodies in the future – including brown dwarves, which have auroras strong enough to be detected through interstellar space.
“Although the ‘drive’ of the aurora borealis on Earth and Jupiter is completely different, showing the links between the two systems for the first time allows us to identify global phenomena and distinguish them from characteristics related to each planet. The magnetospheres of Earth and Jupiter store energy through very different mechanisms,” said Yao. “But when this buildup reaches its breaking point, the two systems release this energy in a surprisingly similar way.”
The research was published in AGU Advances.