Scientists discover high-energy oxygen ions in Jupiter’s innermost radiation belts

Nearly 20 years after NASA’s Galileo mission to Jupiter ended, scientists led by Germany’s Max Planck Institute for Solar System Research (MPS) have unraveled a new secret from the mission’s massive dataset. For the first time, the research team was able to determine without a doubt that the energetic ions surrounding this gas giant are mainly oxygen and sulfur ions.

They are thought to have originated from volcanic eruptions on Jupiter’s moon Europa. Near the orbit of Amalthea’s moon, which orbits Jupiter further inward, the team unexpectedly found high-energy oxygen ion concentrations that could not be explained by Europa’s volcanic activity. A previously unknown ion source must be at work here. The results of the study were published today in the journal Science Advances.

NASA’s Galileo spacecraft reached the Jupiter system in 1995. Equipped with a Heavy Ion Counter (HIC) contributed by Caltech and an Energetic Particle Detector (EPD) developed and built by the Johns Hopkins Applied Physics Laboratory in partnership with MPS, the mission will, over the next eight years, The mission provided a fundamental understanding of the distribution and dynamics of charged particles around the gas giant. However, to protect the spacecraft, it initially only flew over the outer, less extreme regions of the radiation belt. It was only in 2003, shortly before the end of the mission, when the greater risk was justified, that Galileo ventured into the innermost regions within the orbits of the Amasya and Siber satellites. From Jupiter, Amalthea and Thebe are the third and fourth moons of the giant planet. The orbits of Europa and Europa are further out.

With the help of this scientific treasure, the authors of the current study have now been able to determine, for the first time, the composition of ions within the inner radiation belt, as well as the velocities and spatial distribution of ions. Compared to the proton-dominated radiation belts of Earth and Saturn, the regions within Europa’s orbit also contain substantial amounts of heavier oxygen and sulfur ions, with oxygen ions predominant. The energy distribution of heavy ions outside Europa’s orbit suggests that , they were mainly introduced from a more distant region of the radiation belt. The moon Europa, which has more than 400 active volcanoes, may be the main source, repeatedly throwing huge amounts of sulfur and sulfur dioxide into space.

Further inside, within Europa’s orbit, the ionic composition changes dramatically in favor of oxygen. The concentration and energy of oxygen ions there are much higher than expected. In fact, the concentration in this region should be declining because the moons of Amasia and Siber absorb incoming ions, so the orbits of these two small moons form a natural ion barrier. The only explanation for the increase in oxygen ion concentration is that there is another localized source in the innermost region of the radiation belt. As the researchers’ computer simulations have shown, the oxygen released by sulfur ions colliding with fine dust grains in Jupiter’s rings poses one possibility.