Home Technology Ancient data reveal details about Jupiter’s radiation belts

Ancient data reveal details about Jupiter’s radiation belts

Ancient data reveal details about Jupiter's radiation belts

Ancient data reveal details about Jupiter’s radiation belts
Editorial / press release of the Max Planck Institute for Solar System Research
January 14, 2022 Almost 20 years after the end of NASA’s Galileo mission to Jupiter, data from the last phase of the mission, which had been thought to be useless, has found new clues about the nature of the gas giant’s inner radiation belts. The high-energy ions appear to be primarily oxygen and sulfur ions originating from the moon Io.

NASA’s Galileo probe explored the Jupiter system from 1995 to 2003. Image: NASA [Großansicht]

Planets such as Earth, Jupiter and Saturn, which have their own global magnetic field, are surrounded by so-called radiation belts: caught in the magnetic field, fast, charged particles such as electrons, protons and heavier ions whiz around there, forming the invisible, toroidal radiation belts. With their high speeds close to the speed of light, the particles can ionize other molecules when they collide, creating a hostile environment that can also be dangerous for space probes and their instruments. The most extreme radiation belts in the solar system in this respect envelop the gas giant Jupiter. In a new study, an international team of researchers presents the most meaningful study to date of the heavy ions in Jupiter’s inner radiation belts. It is based on data from NASA’s Galileo spacecraft, which explored the Jupiter system from 1995 to 2003. Its last orbits took the probe deep into the innermost radiation belts of the giant planet – and, among other things, close to the moon Amalthea. Like Jupiter’s powerful magnetic field, its radiation belts reach several million kilometers into space; However, the region within the orbit of the moon Europa, i.e. an area with a radius of about 670,000 kilometers around the gas giant, is the scene of the highest particle densities and speeds. Viewed from Jupiter, Europa is the second, after Io, of the four large moons of Jupiter, known as the Galilean moons after their discoverer. With the space probes Pioneer 11 in the mid-1970s, Galileo from 1995 to 2003 and currently Juno, three space missions have ventured into this innermost area of ​​the radiation belts and carried out measurements on site. “Unfortunately, the measurement data from Pioneer 11 and Juno cannot be used to unequivocally conclude which type of ions the space probes encountered there,” says Dr. Elias Roussos from the MPS the current state of research. “Their energies and their origin have therefore been unclear until now,” he adds. Only the now rediscovered measurement data from the last few months of the Galileo mission could remedy the situation. In 1995, NASA’s Galileo spacecraft reached the Jupiter system. Armed with the Heavy Ion Counter (HIC) instruments provided by the California Institute of Technology and the Energetic Particle Detector (EPD) designed and built by the Johns Hopkins Applied Physics Laboratory in collaboration with the MPS, the mission delivered In the eight years that followed, fundamental knowledge was gained about the distribution and dynamics of the charged particles in the vicinity of the gas giant. To protect the spacecraft, however, it initially only flew through the outer, less extreme regions of the radiation belts. It was not until 2003, shortly before the end of the mission, when a greater risk was justifiable, that Galileo penetrated into the inner region and even reached the orbits of the inner moons Amalthea and Thebe. Seen from Jupiter, Amalthea and Thebe are the third and fourth moons of the giant planet. The orbits of Io and Europa are further out. “Actually, it was to be expected that the measurement data from the HIC and EPD from the inner area of ​​the radiation ring would be of little use because of the high radiation exposure. After all, neither of the two instruments was specially developed for use in such a harsh environment,” Roussos describes his expectations when he started working on the current study three years ago. Nevertheless, the researcher wanted to see for himself. As a member of NASA’s Cassini mission, two years earlier he had witnessed Cassini’s last, similarly daring flight maneuvers on Saturn and evaluated the unique data from this final phase of the mission. “The thought of the long-completed Galileo mission came naturally,” Roussos recalls. To his own surprise, among the many useless measurements, there were also some that took a lot of effort to evaluate. With the help of this scientific treasure, the authors of the current study have now been able to determine the type of ions within the inner radiation belts as well as their velocities and spatial distribution for the first time. Unlike in the radiation belts of Earth and Saturn, in which mainly protons occur, the region within the orbit of Jupiter’s moon Io also contains large amounts of the significantly heavier oxygen and sulfur ions, with oxygen ions predominating from both. “The energy distribution of the heavy ions outside of Amalthea’s orbit suggests that they are mostly injected from further outside,” says Roussos. The most notable sources are the moon Io itself, whose more than 400 active volcanoes regularly spew large amounts of sulfur and sulfur dioxide into space, and to a lesser extent the moon Europa. Further in, within Amalthea’s orbit, the ion composition changes dramatically in favor of oxygen. “The concentration and energy of the oxygen ions there is significantly higher than expected,” says Roussos. The ion concentration in this area should actually decrease. For the moons Amalthea and Thebe absorb ions entering from without; their orbits thus form a kind of natural ion barrier. This phenomenon is known from the radiation belts of the Saturn system with its many moons. The only explanation for the increased concentration of oxygen ions is therefore another, local source in the innermost area of ​​the radiation belts. For example, collisions between sulfur ions and the fine dust particles in Jupiter’s rings could release oxygen. The rings, which are much less conspicuous than Saturn’s, extend roughly to the orbit of Thebes. Simulations by the researchers show that this process could explain the finding of oxygen ions. It is also conceivable that low-frequency electromagnetic waves in the vicinity of the innermost radiation belts could heat up oxygen ions to the observed energies. “Currently, it is not possible to distinguish in favor of one of the two possible sources,” says Roussos. However, both possible mechanisms show parallels to the generation of high-energy particles in stellar or extrasolar environments. Roussos hopes this fact will justify future exploration by a dedicated space mission. The results of the study were recently published in the journal Science Advances.

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