A publication in the Journal of Geophysical Research

Elves and sprites on Jupiter?

1 November 2020

This illustration shows what a sprite could look like in Jupiter's atmosphere. Named after a mischievous, quick-witted character in English folklore, sprites last for only a few milliseconds. They feature a central blob of light with long tendrils of light extending down toward the ground and upward. In Earth's upper atmosphere, their interaction with nitrogen give sprites a reddish hue. At Jupiter, where the predominance of hydrogen in the upper atmosphere would likely give them a blue hue. Credits: NASA/JPL-Caltech/SwRI

A study based on data transmitted by NASA's Juno probe shows that transient light episodes called "elves" and "sprites" occur in Jupiter's upper atmosphere. Bertrand Bonfond, Denis Grodent and Jean-Claude Gérard, researchers at the STAR Institute of ULiège, participated in the discovery of this first which has just been published in the Journal of Geophysical Research: Planets (1).

ar from the folkloric representations we know, the "sprites" and the "elves" are, in the meteorological field, transient luminous events. "In both cases, these are peculiar light emissions in the upper atmosphere located above thunderstorms, explains Professor Jean-Claude Gérard, scientific collaborator at the Laboratory of Atmospheric and Planetary Physics (LPAP / Faculty of Science) of the STAR research unit of ULiège. Elves take the form of horizontal discs expanding at the base of the ionosphere, while sprites, made of long vertical filaments similar to the arms of a jellyfish, extend further down into the atmosphere. ". On Earth, these phenomena can illuminate a region of the sky tens of kilometres wide for only a few milliseconds (a fraction of the time it takes to blink). This phenomenon, discovered a few decades ago only on Earth, has probably also been observed on Jupiter, new research shows.

This phenomenon, which had only been observed on Earth so far, was discovered using the UVS (UltraViolet Spectrograph) instrument on board the American probe JUNO - in orbit around Jupiter since 2016. The current accuracy of the observations on Jupiter does not yet allow us to determine their precise shape or altitude," says Denis Grodent, director of the Research Unit and Laboratory. It is thus currently impossible to distinguish between the two kind of events. All we know is that these reddish-coloured phenomena on Earth, due to their interaction with the nitrogen in our upper atmosphere, most probably appear in blue or pink on Jupiter, due to the fact that Jupiter's upper atmosphere is composed mainly of hydrogen. »

The UVS instrument - part of which was designed, built and tested at the Centre Spatial de Liège (CSL) - is an instrument essentially dedicated to the observation of the polar aurora (2) on Jupiter. This discovery is therefore completely accidental. It actually began in the spring of 2020," recalls Bertrand Bonfond, FNRS Research associate at LPAP. We were examining the data that Juno had just transmitted to us with the UVS team when our attention was drawn to a strange spot, which looked like nothing known. We went back to review the older data and found ten more cases. That's when we realised that we had just discovered something new and unusual. Scientists linked to the Juno mission now know what to look for. Comparing the way phenomena occur on Jupiter and Earth will allow researchers to better understand the electrical activity of planetary atmospheres. This is another step forward in understanding some of the mechanisms that may also occur on other planets within and outside our system.

The south pole of Jupiter is seen in this annotated image of data from the ultraviolet spectrograph (UVS) instrument aboard NASA's Juno spacecraft. Bands of bright white and blue near the south pole are Jupiter's southern aurora. But researchers also noticed an unusual bright flash of light well away from the auroral region, highlighted here by the yellow circle at about the 10 o'clock position (between longitudinal lines 270 and 240). Juno scientists believe it could be an indication of a bright, unpredictable, and extremely brief flash of light — known as a transient luminous event — that was triggered by lightning discharges from thunderstorms far below. The data for this UVS image was acquired on April 10, 2020. Credits: NASA/JPL-Caltech/SwRI

Scientific reference

(1) Rohini S. Giles, Thomas K. Greathouse, Bertrand Bonfond , G. Randall Gladstone, Joshua A. Kammer,Vincent Hue,Denis C. Grodent, Jean‐Claude Gérard, Maarten H. Versteeg, Michael H. Wong,Scott J. Bolton, John E. P. Connerney, Steven M. Levin, Possible Transient Luminous Events observed in Jupiter's upper atmosphere, JRG Planet, octobre 2020