From aboard the Juno spacecraft, an instrument run by the Southwest Research Institute that observed the auroras happened to spot a bright flash above Jupiterthe clouds of last spring. The ultraviolet spectrograph (UVS) team studied the data and determined that they had captured a bolide, an extremely bright meteoroid explosion in the gas giant’s upper atmosphere.
“Jupiter suffers a large number of impacts per year, much more than Earth, so impacts themselves are not rare,” said Dr. Rohini Giles of SwRI, lead author of a paper describing these findings in Geophysical. Research Letters. “However, they are so ephemeral that it is relatively rare to see them. You can only see larger impacts from Earth, and you have to be lucky to point a telescope at Jupiter at the exact moment. In the last decade, amateur astronomers have managed to capture six impacts on Jupiter. “
Since Juno arrived at Jupiter in 2016, UVS has been used to study the morphology, brightness, and spectral characteristics of Jupiter’s auroras when the spacecraft rotates near its surface every 53 days. During the course of a 30-second spin, UVS observes a swath of the planet. The UVS instrument has occasionally observed short-lived localized ultraviolet emissions outside the auroral zone, including a singular event on April 10, 2020.
“This observation is from a small snapshot in time: Juno is a spinning spacecraft, and our instrument observed that point on the planet for only 17 milliseconds, and we don’t know what happened to the bright flash outside of that time frame.” Giles said: “But we know we didn’t see it in an earlier or later twist, so it must have been pretty short-lived.”
Previously, UVS had observed a set of eleven bright transient flashes lasting 1 to 2 milliseconds. They were identified as transient light events (TLE), a higher atmospheric phenomenon caused by lightning. The team initially thought that this bright flash could be a TLE, however it was different in two key ways. While it was also short-lived, it lasted at least 17 milliseconds, much longer than a TLE. It also had very different spectral characteristics. The spectra of TLEs and auroras show emissions of molecular hydrogen, the main component of Jupiter’s atmosphere. This racing car event had a smooth “black body” curve, which is what you would expect from a meteor.
“The flash duration and spectral shape are in good agreement with what we expect from an impact,” Giles said. “This bright flash stood out in the data, as it had very different spectral characteristics than the UV emissions from Jupiter’s auroras. In the UV spectrum, we can see that the emission came from a black body with a temperature of 9600 Kelvin, located at an altitude of 140 miles above the planet’s clouds. By looking at the brightness of the bright flash, we estimate that it was caused by an impactor with a mass of 550 to 3,300 pounds. “
Comet Shoemaker-Levy was the largest Jupiter impactor ever observed. The comet broke apart in July 1992 and collided with Jupiter in July 1994, which was closely observed by astronomers around the world and the Galileo spacecraft. A team led by SwRI detected impact-related X-ray emissions from Jupiter’s northern hemisphere, and prominent scars from the impacts persisted for many months.
“Asteroid and comet impacts can have a significant impact on the stratospheric chemistry of the planet: 15 years after impact, Comet Shoemaker Levy 9 was still responsible for 95% of the stratospheric water on Jupiter,” Giles said. “Continuing to observe impacts and estimating overall impact rates is therefore an important element in understanding the makeup of the planet.”
The Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for principal investigator Dr. Scott J. Bolton of the Southwest Research Institute. Juno belongs to POTThe New Frontiers Program, which is administered at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. Lockheed Martin Space in Denver built and operates the spacecraft.