NASA’s Juno spacecraft has been in orbit around Jupiter since 2016. One of its instruments is the ultraviolet spectrograph (UVS), which is primarily used to make ultraviolet images of Jupiter’s auroras. During the first four years of the mission, the UVS instrument has observed 11 transient bright flashes. These flashes look similar to lightning, but are located much higher in the atmosphere than the cloudy regions of Jupiter where lightning is generated. In a paper published in the Journal of Geophysical Research: Planets, researchers suggest that these are observations of transient luminous events in the gas giant’s upper atmosphere. In particular, they suggest that these events are elves, sprites or sprite halos, three types of transient luminous events that produce spectacular flashes of light very high in the Earth’s atmosphere in response to lightning strikes between clouds or between clouds and the ground.
Sprites, named after a mischievous, quick-witted character in English folklore, are transient luminous events triggered by lightning discharges from thunderstorms far below.
On Earth, they occur up to 97 km (60 miles) above intense, towering thunderstorms and brighten a region of the sky tens of miles across, yet last only a few milliseconds.
Almost resembling a jellyfish, sprites feature a central blob of light — on Earth, it’s 24-48 km (15-30 miles) across, with long tendrils extending both down toward the ground and upward.
They, too, brighten the sky for mere milliseconds but can grow larger than sprites — up to 320 km (200 miles) across on Earth. Their colors are distinctive as well.
“On Earth, sprites and elves appear reddish in color due to their interaction with nitrogen in the upper atmosphere,” said lead author Dr. Rohini S. Giles, a postdoctoral researcher at Southwest Research Institute.
“But on Jupiter, the upper atmosphere mostly consists of hydrogen, so they would likely appear either blue or pink.”
Planetary scientists predicted these bright, superfast flashes of light should be present in Jupiter’s immense roiling atmosphere, but their existence remained theoretical.
Dr. Giles and colleagues analyzed data from Juno’s UVS instrument and discovered something unexpected: a bright, narrow streak of ultraviolet emission that disappeared in a flash.
“UVS was designed to characterize Jupiter’s beautiful northern and southern lights,” Dr. Giles said.
“But we discovered UVS images that not only showed Jovian aurora, but also a bright flash of UV light over in the corner where it wasn’t supposed to be.”
“The more our team looked into it, the more we realized Juno may have detected a transient luminous event on Jupiter.”
“We’re continuing to look for more telltale signs of elves and sprites every time Juno does a science pass,” she added.
“Now that we know what we are looking for, it will be easier to find them at Jupiter and on other planets.”
“And comparing sprites and elves from Jupiter with those here on Earth will help us better understand electrical activity in planetary atmospheres.”
Rohini S. Giles et al. Possible Transient Luminous Events observed in Jupiter’s upper atmosphere. Journal of Geophysical Research: Planets, published online October 27, 2020; doi: 10.1029/2020JE006659