A Jupiter Vista from Juno. Credit: NASA / JPL-Caltech / SwRI / MSSS; Processing and License: Kevin M. Gill
On board the Juno spacecraft, an instrument led by the Southwestern Research Institute observed the auroras, a bright flash above Jupiter‘s clouds last spring. The Ultraviolet Spectrograph (UVS) team studied the data and determined that they captured a bolide, an extremely bright meteoroid explosion in the upper atmosphere of the gas giant.
“Jupiter undergoes a large number of impacts per year, much more than Earth, so the impacts themselves are not rare,” says Dr. Rohini Giles, lead author of a paper outlining these findings in Geophysical Research Letters. ‘However, they are so short-lived that it is relatively unusual to see them. Only greater impacts can be seen from Earth, and you should be lucky enough to point a telescope at Jupiter at the right time. In the past decade, amateur astronomers have succeeded in capturing six impacts on Jupiter. ”
Since Juno arrived at Jupiter in 2016, UVS has been used to study the morphology, brightness and spectral properties of Jupiter’s auroras, as the spacecraft is near its surface every 53 days. During a 30-second turn, UVS observes a wave from the planet. The UVS instrument occasionally observed localized ultraviolet emissions outside the auroral area, including a single event on April 10, 2020.
SwRI scientists studied the area imaged by Juno’s UVS instrument on April 10, 2020, and determined that a large meteoroid exploded in a bright fireball in Jupiter’s upper atmosphere. The UVS part contains a part of Jupiter’s northern auroral oval, which appears pure in green, representing hydrogen releases. In contrast, the light spot (see magnification) appears mostly yellow, indicating significant emissions at longer wavelengths. Credit: SwRI
“This observation comes from a small snapshot – Juno is a rotating spacecraft, and our instrument observed that point on the planet for just 17 milliseconds, and we do not know what happened to the bright flash outside that time frame,” Giles said: ‘But we know we did not see it at an earlier or a later turn, so it must have been fairly short-lived.’
Previously, UVS observed a set of eleven bright short-lived flashes that lasted 1 to 2 milliseconds. They have been identified as Transient Luminous Events (TLEs), an atmospheric phenomenon in the upper light caused by lightning. The team initially thought this bright flash could be a TLE, but it was different in two important ways. Although short-lived, it lasted at least 17 milliseconds, much longer than a TLE. It also had very different spectral properties. Spectra of TLEs and auroras contain emissions of molecular hydrogen, the main component of Jupiter’s atmosphere. This volatile event had a smooth “black body” curve, which is expected of a meteor.
“The flash duration and the spectral shape are consistent with what we expect from an impact,” Giles said. ‘This bright flash stood out in the data because it had many other spectral properties than the UV emission of Jupiter’s auroras. From the UV spectrum we can see that the emission comes from black body with a temperature of 9600 Kelvin, located at an altitude of 140 miles above the cloud trees of the planet. By looking at the brightness of the bright flash, we estimate that it was caused by an impact with a mass of 550–3,300 pounds. ”
Comet Shoemaker-Levy was the largest observed Jupiter impact. The comet erupted in July 1992 and collided with Jupiter in July 1994, which was closely observed by astronomers worldwide and the Galileo spacecraft. A SwRI-led team detected impact-related X-ray emissions from Jupiter’s northern hemisphere, and prominent scars from the impact continued for many months.
“Impacts of asteroids and comets can have a significant impact on the planet’s stratospheric chemistry. Comet Shoemaker Levy 9 was still responsible for 95% of the stratospheric water on Jupiter 15 years after the impact,” Giles said. “Continuing to observe the impact and estimate the overall impact rates is therefore an important element in understanding the composition of the planet.
The Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, is managing the Juno mission for chief investigator Dr. Scott J. Bolton, of the Southwest Research Institute. Juno is part of NASANew Frontiers program, run at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the Science Mission board in Washington. Lockheed Martin Space in Denver built and operated the spacecraft.