The study will complement the upcoming flybys of Io by Nasa's Juno spacecraft and will provide insights into its contributions to the plasma environment around Jupiter. Juno made its closest flyby of Io in July, when it came within 22,000 km of it.
"The timing of this project is critical. Over the next year, Juno will buzz past Io several times, offering rare opportunities to combine in situ and remote observations of this complex system," said Dr Kurt Retherford, from Southwest Research Institute (SWRI), which is helping fund the project. The team will use around 4.7 per cent of available time for Hubble observations this cycle, which will be supplemented with 4.8 hours of Webb observing time.
While both are designed to study the cosmos, Webb and Hubble do not have identical capabilities and can therefore be used to complement each other in scientific studies. Webb primarily looks at the universe in the infrared, while Hubble studies it primarily at optical and ultraviolet wavelengths, although it has some infrared capability. Webb also has a much bigger mirror than Hubble.
"We hope to gain new insights into Io's dramatic volcanism, plasma-moon interactions and the neutral gas and plasma populations that propagate through Jupiter's vast magnetosphere and trigger intense Jovian auroral emissions," Retherford added.
Io's escaping atmosphere is the dominant source of material in the Jovian magnetosphere, a vast bubble of charged particles swirling around the gas giant. The connection between Io's volcanos, surface volatiles and atmosphere and Jupiter's ionosphere has remained difficult to quantify and understand until now.
Dr Fran Bagenal, the project's co-principal investigator from the University of Colorado Boulder, said: "For example, how much sulphur is transported from Io to Europa's surface? How do auroral features on Io compare with aurora on Earth — the northern lights — and Jupiter?"
Io is the innermost large moon of Jupiter and supplies most of the charged particles in the planet's magnetosphere. The Io Plasma Torus (IPT) is a doughnut-shaped cloud of ions and electrons surrounding Jupiter, created when atmospheric gases escaping from Io are ionised. Electrons collide with the ions, which absorb energy from the collisions and release it as ultraviolet light, which can be detected by telescopes.
"Most of these materials don't actually escape straight out of the volcanoes, but rather are associated with the sublimation of sulphur dioxide frost from Io's dayside surface," said Caltech's Dr Katherine de Kleer, another co-investigator with expertise in James Webb data analysis. "The interaction between Io's atmosphere and the surrounding plasma provides the escape mechanism for gases released from the moon's frozen surface."
Juno's primary mission studied Jupiter's interior, magnetosphere and aurora, while its extended mission included flybys of the Galilean moons such as Io, Callisto, Europa and Ganymede. While the Europa Clipper and Jupiter Icy Moons Explorer (JUICE) missions are scheduled to arrive at Jupiter in 2029-2031, neither of these missions fly by Io.
"The chance for a holistic approach to Io investigations has not been available since a series of Galileo spacecraft flybys in 1999-2000 were supported by Hubble with a prolific 30-orbit campaign," Retherford said. "The combination of Juno's intensive in situ measurements with our remote-sensing observations will undoubtedly advance our understanding of Io's role in driving coupled phenomena in the Jupiter system."
