NASA's Juno Mission Maps Jupiter's Radiation Using Danish Technology

This achievement was made possible through data gathered by Juno's Advanced Stellar Compass (ASC), developed by the Technical University of Denmark, and the Stellar Reference Unit (SRU), built by Leonardo SpA in Florence, Italy. These two instruments work in tandem to provide a detailed understanding of Jupiter's radiation environment at various energy levels.

Both the ASC and SRU are low-light cameras typically used for deep-space navigation. However, the Juno science team repurposed them as radiation detectors, unlocking new ways to study Jupiter's harsh environment.

"On Juno we try to innovate new ways to use our sensors to learn about nature, and we have used many of our science instruments in ways they were not designed for," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. "This is the first detailed radiation map of the region at these higher energies, which is a major step in understanding how Jupiter's radiation environment works. This will help planning observations for the next generation of missions to the Jovian system."

Counting Fireflies
Juno's ASC consists of four star cameras mounted on the spacecraft's magnetometer boom. While their primary function is to image stars and determine the spacecraft's orientation in space, these cameras have also become valuable tools for detecting high-energy particles within Jupiter's magnetosphere. The ASC captures images of "hard radiation"-ionizing particles with enough energy to penetrate the camera's shielding.

"Every quarter-second, the ASC takes an image of the stars," explained Juno scientist John Leif Jorgensen of the Technical University of Denmark. "Very energetic electrons that penetrate its shielding leave a telltale signature in our images that looks like the trail of a firefly. The instrument is programmed to count the number of these fireflies, giving us an accurate calculation of the amount of radiation."

Juno's varied orbital path has allowed it to explore nearly every region of space surrounding Jupiter.

The ASC data reveals that there is more high-energy radiation than previously expected near Europa's orbit. Furthermore, it shows that higher concentrations of energetic electrons are found on the side of Europa facing the direction of its orbit. This is due to Jupiter's rotation, which causes most electrons in its magnetosphere to overtake Europa, while the highest-energy electrons move against the rotation, impacting the moon's leading edge.

The ASC has also contributed significantly to Juno's mission even before it reached Jupiter, having been used to measure interstellar dust and detect a previously unknown comet.

Dust Rings
The SRU, like the ASC, has been employed as a radiation detector and low-light imager. Data from both instruments indicates that the small "shepherd moons" near Jupiter's rings interact with the planet's radiation environment. When Juno passes along magnetic field lines connected to these moons or dense dust, the radiation levels measured by the ASC and SRU drop significantly. The SRU has also been capturing rare low-light images of the rings from Juno's unique vantage point.

"There is still a lot of mystery about how Jupiter's rings were formed, and very few images have been collected by prior spacecraft," said Heidi Becker, lead co-investigator for the SRU and a scientist at NASA's Jet Propulsion Laboratory in Southern California, which manages the mission. "Sometimes we're lucky and one of the small shepherd moons can be captured in the shot. These images allow us to learn more precisely where the ring moons are currently located and see the distribution of dust relative to their distance from Jupiter."