NASA’s Juno spacecraft has captured what appears to be “sprites” or “elves” frolicking in the atmosphere of Jupiter for the first time. Perhaps the king of planets has decided to join in the Halloween fun this year?
The new results from Juno suggest these lightning-like electrical outbursts occur in the upper reaches of Jupiter's tumultuous atmosphere. It’s the first time they have ever been observed on another planet, the Juno team report in the Journal of Geophysical Research: Planets.
On Earth, these bright flashes are caused by thunderstorms, with lightning strikes either creating red tendrils called “sprites” or glowing disks known as “elves”. It was suspected that these transient luminous events (TLEs) may occur on Jupiter, as it's well known to have lightning storms of its own, but they had never been spotted before now.
Last summer, researchers using Juno's ultraviolet spectrograph instrument (UVS) to observe Jupiter’s aurorae were surprised to catch a bright narrow streak of ultraviolet emission that disappeared just as quickly.
"UVS was designed to characterize Jupiter's beautiful northern and southern lights," said Rohini Giles, lead author of the paper. "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 TLE on Jupiter."
Lasting for just milliseconds, sprites on Earth are triggered by lightning charges from thunderstorms rumbling around 100 kilometers (60 miles) below and can stretch 50 kilometers (30 miles) across, like giant red sky jellyfish. Elves (necessarily short for Emission of Light and Very Low-Frequency perturbations due to Electromagnetic Pulse Sources) appear as huge flat disks and can reach an incredible 320 kilometers (200 miles) across, but again are over in a flash.
Searching back over data from the last four years of the Juno mission, the team found 11 bright events that they suspect are TLEs because they were observed in a region of Jupiter known to form thunder and lightning and lasted for just milliseconds. They ruled out the possibility these events were just mega-bolts of lightning because they were found 300 kilometers (186 miles) above the water clouds where Jupiter's lightning usually forms. The UVS also detected high hydrogen emissions in the bright flashes.
"On Earth, sprites and elves appear reddish in color due to their interaction with nitrogen in the upper atmosphere," said Giles. "But on Jupiter, the upper atmosphere mostly consists of hydrogen, so they would likely appear either blue or pink."
Now that the researchers know what they are looking for, it should be easier to find them on Jupiter, and perhaps even other planets that we know form lightning like Saturn or exoplanet HAT-P-11b. Finding sprites and elves on other worlds doesn't just mean a galactic-wide Halloween party, it's another step towards understanding electrical activity in planetary atmospheres.