Oxygen ions in Jupiter's innermost radiation belts

Date:
January 12, 2022
Source:
Max Planck Institute for Solar System Research
Summary:
Researchers find high-energy oxygen and sulfur ions in Jupiter's
inner radiation belts -- and a previously unknown ion source.



FULL STORY ========================================================================== Nearly 20 years after the end of NASA's Galileo mission to Jupiter,
scientists led by the Max Planck Institute for Solar System Research
(MPS) in Germany have unlocked a new secret from the mission's extensive
data sets. For the first time, the research team was able to determine
beyond doubt that the high-energy ions surrounding the gas giant as part
of its inner radiation belt are primarily oxygen and sulfur ions. They
are thought to have originated in volcanic eruptions on Jupiter's
moon Io. Near the orbit of the moon Amalthea, which orbits Jupiter
further inward, the team discovered an unexpectedly high concentration
of high-energy oxygen ions that cannot be explained by Io'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.


========================================================================== Planets like Earth, Jupiter, and Saturn with global magnetic fields of
their own are surrounded by so-called radiation belts: Trapped in the
magnetic field, fast moving charged particles such as electrons, protons,
and heavier ions whiz around thus forming the invisible, torus-shaped
radiation belts. With their high velocities reaching almost the speed
of light, the particles can ionize other molecules when they collide,
creating a hazardous environment that can also be dangerous to space
probes and their instruments. In this respect, the gas giant Jupiter
sports the most extreme radiation belts in the Solar System.

In their new publication, researchers from the MPS, the California
Institute of Technology (USA), the Johns Hopkins Applied Physics
Laboratory (USA), the Laboratory of Instrumentation and Experimental
Particle Physics (Portugal), and the Academy of Athens (Greece) now
present the most comprehensive study to date of the heavy ions in
Jupiter's inner radiation belts.

Like Jupiter's massive magnetic field, its radiation belts extend several million kilometers into space; however, the region within the moon's
orbit of Europa, an area with a radius of about 670,000 kilometers
around the gas giant, is the scene of the highest energetic particle
densities and velocities. Viewed from Jupiter, Europa is the second of
the four large Jovian satellites named "Galilean moons" after their
17th century discoverer. Io is the innermost Galilean moon. With the
space probes Pioneer 11 in the mid-1970s, Galileo from 1995 to 2003,
and currently Juno, three space missions have so far ventured into
this innermost part of these radiation belts and performed in-situ measurements. "Unfortunately, the data from Pioneer 11 and Juno do
not allow us to conclude beyond doubt what kind of ions the spacecraft encountered there," says MPS scientist Dr. Elias Roussos, lead author
of the new study, describing the current state of research. "Therefore,
their energies and origin were also unclear until now," he adds. Only
the now rediscovered data from the last months of the Galileo mission
is detailed enough to improve this situation.

Venturing into the inner radiation belts NASA's Galileo spacecraft reached
the Jupiter system in 1995. Equipped with the Heavy Ion Counter (HIC), contributed by the California Institute of Technology, and the Energetic Particle Detector (EPD), developed and built by Johns Hopkins Applied
Physics Laboratory in collaboration with the MPS, the mission spent the following eight years providing fundamental insights into the distribution
and dynamics of charged particles around the gas giant. However, to
protect the spacecraft, it initially flew solely through the outer,
less extreme regions of the radiation belts. Only in 2003, shortly
before the end of the mission, when a greater risk was justifiable,
Galileo ventured into the innermost region within the orbits of the
moons Amalthea and Thebe. Viewed from Jupiter, Amalthea and Thebe are
the third and fourth moons of the giant planet. The orbits of Io and
Europa lie farther outward.

"Because of the exposure to strong radiation, it was to be expected
that the measurement data from HIC and EPD from the inner region of
the radiation belt would be heavily corrupted. After all, neither of
these two instruments was specifically designed to operate 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, he had witnessed Cassini's final, similarly daring orbits at Saturn two years
earlier and analyzed the unique data from that final mission phase. "The thought of the long-completed Galileo mission kept coming to my mind,"
Roussos recalls. To his own surprise, among many unusable data sets there
were also some that could be processed and analyzed with much effort.

Enigmatic oxygen ions With the help of this scientific treasure, the
authors of the current study have now been able to determine for the
first time the ion composition within the inner radiation belts, as well
as the ions' velocities and spatial distribution. In contrast to the
radiation belts of Earth and Saturn, which are dominated by protons,
the region within the orbit of Io also contains large amounts of the
much heavier oxygen and sulfur ions, with oxygen ions prevailing among
the two. "The energy distribution of the heavy ions outside the orbit of Amalthea suggests that they are largely introduced from a more distant
region of the radiations belts," Roussos says. The moon Io with its
more than 400 active volcanoes, which repeatedly hurl large amounts of
sulfur and sulfur dioxide into space, and to a lesser extent, Europa,
are likely the main sources.

Further inward, within Amalthea's orbit, the ion composition changes drastically in favor of oxygen. "The concentration and the energy of
oxygen ions there is much higher than expected," Roussos says. Actually,
the concentration should be decreasing in this region, as the moons
Amalthea and Thebe absorb incoming ions; the two small moons' orbits
thus form a kind of natural ion barrier. This behavior is, for example,
known from radiation belts of the Saturnian system with its many moons.

The only explanation for the increased concentration of oxygen ions is therefore another, local source in the innermost region of the radiation
belts.

The release of oxygen following the collisions of sulfur ions with the
fine dust particles of Jupiter's rings constitute one possibility,
as the researchers' computer simulations show. The rings, which are
much fainter than the Saturnian ones, extend approximately as far as
the orbit of Thebe. However, it is also conceivable that low-frequency electromagnetic waves in the magnetospheric environment of the innermost radiation belts heat oxygen ions to the observed energies.

"Currently, it is not possible to distinguish in favor of either of these possible sources," Roussos says. ?ny of these two candidate mechanisms, nevertheless, have parallels to high energy particle production in
stellar or extrasolar environments, further establishing that Jupiter's radiation belts extend into the astrophysical realm, a fact that the
researcher hopes would justify their future exploration with a dedicated
space mission.

========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Solar_System_Research. Note: Content may be
edited for style and length.


========================================================================== Related Multimedia:
* Enigmatic_oxygen_ions ========================================================================== Journal References:
1. Elias Roussos, Christina Cohen, Peter Kollmann, Marco Pinto, Norbert
Krupp, Patricia Gonc,alves, Konstantinos Dialynas. A source of very
energetic oxygen located in Jupiter's inner radiation belts. Science
Advances, 2022; 8 (2) DOI: 10.1126/sciadv.abm4234
2. Elias Roussos, Oliver Allanson, Nicolas Andre', Bruna Bertucci,
Graziella
Branduardi-Raymont, George Clark, Konstantinos Dialynas, Iannis
Dandouras, Ravindra T. Desai, Yoshifumi Futaana, Matina Gkioulidou,
Geraint H. Jones, Peter Kollmann, Anna Kotova, Elena A. Kronberg,
Norbert Krupp, Go Murakami, Quentin Ne'non, Tom Nordheim, Benjamin
Palmaerts, Christina Plainaki, Jonathan Rae, Daniel Santos-Costa,
Theodore Sarris, Yuri Shprits, Ali Sulaiman, Emma Woodfield, Xin
Wu, Zonghua Yao. The in- situ exploration of Jupiter's radiation
belts. Experimental Astronomy, 2021; DOI: 10.1007/s10686-021-09801-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220112145031.htm
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