Juno, a NASA spacecraft, has discovered the dark sources of one of Jupiter’s spectacular light displays

New findings from the NASA Juno instrument Ultraviolet Spectrograph show for the first time that auroral dawn storms are formed – dawn unprecedented for the dazzling auroras of Jupiter. These huge, intermittent light displays occur in each of the Jovian poles. Only land and earth-orbiting observers, including the NASA Hubble Space Telescope, have previously observed this. The findings of this analysis have been published in AGU Advances on 16 March.

Dawn storms are short-lived but extreme brightening and broadenings of Jupiter’s main auroral oval—and an oblong curtain of light that circles both poles—near where the atmosphere emerges from the darkness in the early morning area, first discovered by Hubble’s Faint Object Camera in 1994. Prior to Juno, reports of Jovian ultraviolet auroras provided only side images, concealing anything unfolding on the planet’s nightside.

“Observing Jupiter’s aurora from Earth does not allow you to see beyond the branch, into Jupiter’s poles at night. Other spacecraft explorations—Voyager, Galileo, and Cassini—occurred from comparatively great distances and did not travel over the poles, so they could not see the whole image” Bertrand Bonfond, the study’s lead author and a professor at the Belgium’s University of Liège. “That’s why Juno data is such a game-changer, giving us a deeper view of what’s going on on the nightside, where dawn storms are born.”

Researchers discovered that dawn storms form on the nightside of the gas giant. The soon-to-be dawn storm rotates with the earth into the dayside, where these diverse and extremely bright auroral characteristics become much more luminous, releasing hundreds to thousands of gigatonnes of ultraviolet light into space. The increase in visibility indicates that dawn storms are depositing at least ten times more energy into Jupiter’s upper atmosphere than normal aurora.

“When we looked at the whole dawn storm series, we couldn’t help but find that they are very similar to a kind of terrestrial aurora called substorms,” said Zhonghua Yao, co-author of the study and a professor at the University of Liège.” Substorms are the consequence of short disruptions in the magnetosphere of the earth—the magnet field-controlled area of space—which release energy high in the ionosphere of the world. The correlation between Jovian and earthly substorms is remarkable because of the vastly different magnetospheres of Jupiter and Earth.

On earth, the main link between the Solar Wind, the flux of charged particles from the Sun, and the magnetic field are dominated by the magnetosphere. The magnetosphere on earth. The magnetosphere of Jupiter is mostly inhabited by ions fleeing from the volcanic moon lo, which are then ionized and frozen by its magnetic field around the gas giant.

These recent discoveries would enable scientists to investigate the variations and similarities that drive the emergence of aurora, offering a deeper explanation of how these most spectacular of planetary events occur on worlds both within and outside our solar system.

“Jupiter is blessed with immense strength. The energy in these dawn aurorae is yet another demonstration of how powerful this vast planet really is” said Scott Bolton of the Southwest Research Institute in San Antonio, Juno’s principal investigator. “The Juno project is actively updating the book about how giant planets operate, and the dawn storm discoveries are yet another surprise. We’re looking forward to evening more new insights and findings thanks to NASA’s latest mission expansion.”