Using data collected by the Advanced Stellar Compass (ASC) and Stellar Reference Unit (SRU) on NASA’s Juno spacecraft, scientists have created the first complete 3D radiation map of the Jupiter system. The map characterizes the intensity of high-energy particles near the orbit of the icy moon Europa and shows how the radiation environment is shaped by small moons orbiting close to Jupiter’s rings.
This diagram shows a model of radiation intensity at different points on the Juno spacecraft’s orbit around Jupiter. Image credit: NASA / JPL-Caltech / DTU.
“With Juno, we’ve been trying to invent new ways to use sensors to learn about nature, and we’ve been using many of our science instruments in ways that were not originally intended,” said Juno principal investigator Dr. Scott Bolton, a planetary scientist at the Southwest Research Institute.
“This is the first detailed radiation map of this high-energy region and marks a major step forward in understanding how Jupiter’s radiation environment works.”
“It’s significant that we’ve been able to map this area in detail for the first time, because we don’t have instruments designed to look for radiation.”
“This map will help plan observations for future missions to the Jovian system.”
Juno’s ASC instrument, consisting of four star cameras mounted on the spacecraft’s magnetometer boom, takes images of the stars to determine the spacecraft’s orientation in space.
But the instrument is also a valuable detector for detecting the flow of high-energy particles within Jupiter’s magnetosphere.
The cameras record “hard radiation” – ionizing radiation that affects the spacecraft with enough energy to penetrate the ASC’s shielding.
“The ASC takes an image of the star every quarter of a second,” said Juno scientist Dr. John Leif Jorgensen, a researcher at the Technical University of Denmark.
“The highly energetic electrons that penetrate the shield leave distinctive signatures in our images, like firefly trails.”
“The device is programmed to count the number of fireflies, allowing us to accurately calculate the amount of radiation.”
Juno’s orbit is constantly changing, so the spacecraft has traversed nearly every region of space near Jupiter.
The ASC data suggests that there is more very high-energy radiation, relative to low-energy radiation, near Europa’s orbit than previously thought.
The data also confirm that there are more energetic electrons on the side of Europa facing in the direction of its orbital motion than on the rear side of Europa.
This is because most of the electrons in Jupiter’s magnetosphere pass Europa from behind due to the planet’s rotation, but the very energetic electrons flow backwards, like a fish swimming upstream, and slam into the front of Europa.
The Jupiter radiation data is not the ASC’s first scientific contribution to the mission: even before it arrived at Jupiter, ASC data was used to measure interstellar dust bombarding Juno.
Using the same dust-detection techniques, the imager also discovered a previously undiscovered comet, identifying tiny pieces of the spacecraft ejected by fine dust particles that collided with Juno at high speed.
Like Juno’s ASC, the SRU will act as a radiation detector and low-light imaging instrument.
Data from both instruments show that, like Europa, small shepherd moons that orbit inside or near the edges of Jupiter’s rings and help maintain their shape also appear to interact with the planet’s radiation environment.
If the spacecraft flies over magnetic field lines that connect to ring moons or dense dust, the radiation dose to both the ASC and SRU drops sharply.
The SRU is also collecting rare low-light images of the rings from Juno’s unique vantage point.
“Many mysteries remain about how Jupiter’s rings formed, and very few images have been collected by previous spacecraft,” said SRU principal investigator Dr. Heidi Becker, a scientist at NASA’s Jet Propulsion Laboratory.
“If you’re lucky, you might even be able to capture a little shepherd moon in your photo.”
“These images allow us to get a better idea of where the ring moons are currently located and to see the distribution of dust relative to the distance from Jupiter.”
of Survey results Will be published in the journal Geophysical Research Letters.
Source: www.sci.news
