Danish Instrument Helps NASA’s Juno Spacecraft See Radiation
“Every quarter-second, the ASC takes an image of the stars,” said Juno scientist John Leif Jørgensen 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.”
Because of Juno’s ever-changing orbit, the spacecraft has traversed practically all regions of space near Jupiter.
ASC data suggests that there is more very high-energy radiation relative to lower-energy radiation near Europa’s orbit than previously thought. The data also confirms that there are more high-energy electrons on the side of Europa facing its orbital direction of motion than on the moon’s trailing side. This is because most of the electrons in Jupiter’s magnetosphere overtake Europa from behind due to the planet’s rotation, whereas the very high-energy electrons drift backward, almost like fish swimming upstream, and slam into Europa’s front side.
Jovian radiation data is not the ASC’s first scientific contribution to the mission. Even before arriving at Jupiter, ASC data was used to determine a measurement of interstellar dust impacting Juno. The imager also discovered a previously uncharted comet using the same dust-detection technique, distinguishing small bits of the spacecraft ejected by microscopic dust impacting Juno at a high velocity.
Dust Rings
Like Juno’s ASC, the SRU has been used as a radiation detector and a low-light imager. Data from both instruments indicates that, like Europa, the small “shepherd moons” that orbit within or close to the edge of Jupiter’s rings (and help to hold the shape of the rings) also appear to interact with the planet’s radiation environment. When the spacecraft flies on magnetic field lines connected to ring moons or dense dust, the radiation count on both the ASC and SRU drops precipitously. The SRU is also collecting 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.”
More About the Mission
NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. The Technical University of Denmark designed and built the Advanced Stellar Compass. The Stellar Reference Unit was built by Leonardo SpA in Florence, Italy. Lockheed Martin Space in Denver built and operates the spacecraft.
More information about Juno is available at:
https://www.nasa.gov/juno
