Groundbreaking observations from the James Webb Space Telescope have revealed hydrogen peroxide on Europa and ongoing volcanic eruptions on Europa, deepening our understanding of Jupiter's moons and the wider solar system.
The James Webb Space Telescope (JWST), with its sensitive infrared camera and high-resolution spectrometer, has revealed new secrets about Jupiter's Galilean moons, especially the largest moon, Europa, and the volcano's most active Io.
In two separate publications, astronomers involved in JWST's Early Release Science Program report that they detected hydrogen peroxide for the first time on Europa and sulfur smoke on Europa, both as a result of Jupiter's influences.
Imke de Pater, professor emeritus of astronomy and earth and planetary sciences at the University of California, Berkeley, said: "This shows that we can do incredible scientific research on solar system objects with the James Webb Space Telescope, even if the objects are really very bright, like Jupiter, but also when you look at something very faint next to Jupiter." De Pat and Thierry Fouchet of the Paris Observatory are co-principal investigators of the Early Release Science solar system observation team, one of 13 that have been given early access to the telescope.
The Ganymede spectrum measured by JWST shows the light absorption characteristics of hydrogen peroxide molecules around the poles. The circle outlines the surface of the Moon. Source: Samantha Trumbo, Cornell University
Samantha Trumbo, a 51 Pegasi b postdoctoral researcher at Cornell University, led the study of Europa, which was published July 21 in the journal Science Advances. Using measurements captured by the Near-Infrared Spectrometer (NIRSpec) on JWST, the team detected the absorption of light by hydrogen peroxide (H2O2) around the Moon's north and south poles, the result of charged particles around Jupiter and Europa hitting the ice covering the Moon.
"JWST revealed the presence of hydrogen peroxide at both poles of Ganymede, which is the first indication that charged particles distributed along the funnel-like distribution of Ganymede's magnetic field are preferentially changing the surface chemistry of Ganymede's crown," Trump said. "
Astronomers believe that peroxides are created by charged particles hitting frozen water ice around the poles and breaking water molecules into pieces — a process known as radiation decomposition — and then the water molecules recombine to form H2O2. They suspect that radiation decomposition occurs mainly at the poles of Ganymede, because Ganymede, unlike other moons in the solar system, has a magnetic field that directs charged particles to the poles.
A close-up of Europa (left) and Europa (right), the former taken by NASA's Juno spacecraft in 2021, and Europa's Galileo spacecraft in 1997. Source: NASA/JPL/USGS
She added: "Just as Earth's magnetic field directs charged particles from the Sun to the highest latitudes, resulting in auroras, Europa's magnetic field does the same for charged particles from Jupiter's magnetosphere." These particles not only produce auroras in Europa, but also have an impact on the ice surface. "
Thrumbo and Michael Brown, a professor of planetary astronomy at Caltech (where Trenbo recently received his Ph.D.), earlier studied hydrogen peroxide on Europa, another of Jupiter's four Galilean moons. However, hydrogen peroxide can be detected on most of Europa's surface, in part because Europa does not have a magnetic field to protect the surface from fast-moving particles around Jupiter.
Trenbo said: "This can be a very important and extensive process. These observations of Ganymede provide a critical window into how the radiative breakdown of this water might drive chemical reactions in ice bodies throughout the outer solar system, including neighboring Europa and Callisto (the fourth Galileo satellite)."
"This helps to really understand how this so-called radiation breakdown works, and it does work as one would expect based on laboratory experiments on Earth," de Pat said. "
Infrared images of Europa by JWST show hot volcanic eruptions from Kanehekili Fluctus (center) and Loki Patera (right). The circle outlines the lunar surface. Source: Imke de Pater, University of California, Berkeley
In a second paper, accepted for publication in JGR: Planets, a journal of the American Geophysical Union, de Pater and her colleagues report new Webb observations of Europa, which show several ongoing eruptions, including the brightening of a volcanic complex called Loki Patera and an unusually bright eruption of Kanehekili Fluctus. Since Io's only volcanically active moon in the solar system — Jupiter's gravitational thrust and pull heat it up — similar studies offer planetary scientists a different perspective than studying Earth's volcanoes.
Webb will observe Europa again with a near-infrared telescope in August. Both the upcoming observations and previous observations on November 15, 2022 were made while Callisto was in Jupiter's shadow, so the light reflected by Jupiter would not obscure the light emitted by Ganymede.
De Pat also noted that the brightening of Rocky Paterra coincides with the observed eruption period, which brightens on average every 500 Earth days for several months. She judged this way because the Moon was not bright when she observed it with the Keck telescope in August and September 2022, and it was not bright when another astronomer observed the Moon in April-July 2022. Only JWST caught the event.
"The Webb observations show that the eruption has actually started and it's much brighter than what we saw in September," she said. "
While DePart's primary focus is on the Ganymede system — its rings, small moons, and larger moons Europa and Ganymede — she and the rest of the early science team of about 80 astronomers are also using JWST to study the planetary systems of Saturn, Uranus and Neptune.