NASA’s Juno reveals the dark origins of one of Jupiter’s great light shows

New results from NASA’s Juno mission ultraviolet spectrograph instrument reveal for the first time the birth of dawn auroral storms, the morning glow unique to Jupiter’s spectacular auroras. These immense, transient displays of light occur at both Jovian poles and have previously only been observed by ground-based and Earth-orbiting observatories, notably NASA’s Hubble Space Telescope. The results of this study were published on March 16 in the journal AGU Advances.

First discovered by Hubble’s Faint Object Camera in 1994, dawn storms consist of a short-lived but intense glow and magnification of Jupiter’s main auroral oval, an oblong curtain of light that surrounds both poles, near where the atmosphere emerges from the darkness in the region of the early hours of the morning. . Before Juno, observations of the Jovian ultraviolet aurora offered only side views, hiding everything that was happening on the night side of the planet.

“Observing Jupiter’s aurora from Earth does not allow you to see beyond limb, on the night side of Jupiter’s poles. The explorations by other spacecraft (Voyager, Galileo, Cassini) occurred from relatively great distances and did not fly. over the poles, as far as they could. I don’t see the whole picture, “said Bertrand Bonfond, a researcher at the University of Liege in Belgium and lead author of the study. “That is why the Juno data is a true game changer, allowing us to better understand what is happening on the night side, where the dawn storms are born.”

The researchers found that dawn storms are born on the night side of the gas giant. As the planet rotates, the future dawn storm rotates with it to the daytime side, where these complex and intensely bright auroral features become even more luminous, emitting hundreds to thousands of gigawatts of ultraviolet light into space. The jump in brightness implies that dawn storms are dumping at least 10 times more energy into Jupiter’s upper atmosphere than typical auroras.

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

Substorms are the result of brief disturbances in Earth’s magnetosphere, the region of space controlled by the planet’s magnetic field, releasing energy high up in the planet’s ionosphere. The similarity between the Terrestrial and Jovian substorms is striking because the magnetospheres of Jupiter and Earth are radically different. On Earth, the magnetosphere is essentially controlled by the interaction of the solar wind, the stream of charged particles that flow from the Sun, with the Earth’s magnetic field. Jupiter’s magnetosphere is populated primarily by particles escaping from the volcanic moon Io, which then ionize and become trapped around the gas giant through its magnetic field.

These new findings will allow scientists to further study the differences and similarities that drive the formation of the aurora, providing a better understanding of how these most beautiful planetary phenomena occur on worlds both within our solar system and beyond.

“The power that Jupiter possesses is amazing. The energy in these dawn auroras is yet another example of how powerful this giant planet really is,” said Scott Bolton, Juno principal investigator at the Southwest Research Institute in San Antonio. “The dawn storm revelations are another surprise from the Juno mission, which is constantly rewriting the book on how giant planets work. With NASA’s recent mission extension, we expect many more new insights and discoveries.”