James Webb Space Telescope sees Jupiter moons in a new light

With its delicate infrared cameras and high-resolution spectrometer, the James Webb House Telescope (JWST) is revealing new secrets and techniques of Jupiter’s Galilean satellites, particularly Ganymede, the most important moon, and Io, essentially the most volcanically energetic.

In two separate publications, astronomers who’re a part of JWST’s Early Launch Science program report the primary detection of hydrogen peroxide on Ganymede and sulfurous fumes on Io, each the results of Jupiter’s domineering affect.

“This reveals that we are able to do unimaginable science with the James Webb House Telescope on photo voltaic system objects, even when the thing is actually very brilliant, like Jupiter, but additionally while you take a look at very faint issues subsequent to Jupiter,” mentioned Imke de Pater, professor emerita of astronomy and earth and planetary science on the College of California, Berkeley. De Pater and Thierry Fouchet from the Paris Observatory are co-principal investigators for the Early Launch Science photo voltaic system statement workforce, considered one of 13 groups given early entry to the telescope.

Samantha Trumbo, a 51 Pegasi b postdoctoral fellow at Cornell College, led the research of Ganymede, which was printed July 21 within the journal Science Advances. Utilizing measurements captured by the close to infrared spectrometer (NIRSpec) on JWST, the workforce detected the absorption of sunshine by hydrogen peroxide — H2O2 — across the north and south poles of the moon, a results of charged particles round Jupiter and Ganymede impacting the ice that blankets the moon.

“JWST revealing the presence of hydrogen peroxide at Ganymede’s poles reveals for the primary time that charged particles funneled alongside Ganymede’s magnetic area are preferentially altering the floor chemistry of its polar caps,” Trumbo mentioned.

photos of gray moon Ganymede and yellow-orange Io against black background
Closeup photographs of Ganymede (left), taken by NASA’s Juno spacecraft in 2021, and Io (proper), taken by NASA’s Galileo spacecraft in 1997.
Picture credit score: NASA/JPL/USGS

The astronomers argue that the peroxide is produced by charged particles hitting the frozen water ice across the poles and breaking the water molecules into fragments — a course of known as radiolysis — which then recombine to kind H2O2. They suspected that radiolysis would happen primarily across the poles on Ganymede as a result of, not like all different moons in our photo voltaic system, it has a magnetic area that directs charged particles towards the poles.

“Similar to how Earth’s magnetic area directs charged particles from the solar to the best latitudes, inflicting the aurora, Ganymede’s magnetic area does the identical factor to charged particles from Jupiter’s magnetosphere,” she added. “Not solely do these particles lead to aurorae at Ganymede, as effectively, however additionally they influence the icy floor.”

Trumbo and Michael Brown, professor of planetary astronomy at Caltech, the place Trumbo just lately acquired her Ph.D., had earlier studied hydrogen peroxide on Europa, one other of Jupiter’s 4 Galilean satellites. On Europa, nevertheless, the peroxide was detectable over a lot of the floor, maybe, partly, as a result of it has no magnetic area to guard the floor from the fast-moving particles zipping round Jupiter.

“That is probably a extremely vital and widespread course of,” Trumbo mentioned. “These observations of Ganymede present a key window to know how such water radiolysis may drive chemistry on icy our bodies all through the outer photo voltaic system, together with on neighboring Europa and Callisto (the fourth Galilean moon).”

“It helps to truly perceive how this so-called radiolysis works and that, certainly, it really works as folks anticipated, based mostly on lab experiments on Earth,” de Pater mentioned.

Io’s sulfurous setting

In a second paper, accepted for publication within the journal JGR: Planets, a publication of the American Geophysical Union, de Pater and her colleagues report new Webb observations of Io that present a number of ongoing eruptions, together with a brightening at a volcanic complicated known as Loki Patera and an exceptionally brilliant eruption at Kanehekili Fluctus. As a result of Io is the one volcanically energetic moon within the photo voltaic system — Jupiter’s gravitational push and pull heats it up — research like this give planetary scientists a special perspective than may be obtained by finding out volcanos on Earth.

bluish images of Io, with reddish blotches showing volcanic gases
JWST measurements obtained in November 2022 overlaid on a map of Io’s floor. Thermal infrared measurements (proper) present a brightening of Kanekehili Fluctus, a big and, in the course of the statement interval, very energetic volcanic space on Io. Spectral measurements (left) present forbidden infrared emissions from sulfur monoxide centered on the volcanic space. The coincidence confirms a principle that SO is produced in volcanic vents and, within the very skinny environment of Io, stay round lengthy sufficient to emit the forbidden line that might usually be suppressed by collisions with different molecules within the environment.
Picture credit score: Chris Moeckel and Imke de Pater, UC Berkeley; Io map courtesy of USGS

For the primary time, the researchers have been in a position to hyperlink a volcanic eruption — at Kanehekili Fluctus — to a particular emission characteristic produced by so-called “forbidden” transitions of the gasoline sulfur monoxide (SO).

Sulfur dioxide (SO2) is the principle part of Io’s environment, coming from sublimation of SO2 ice, in addition to ongoing volcanic eruptions, just like the manufacturing of SO2 by volcanos on Earth. The volcanos additionally produce SO, which is way tougher to detect than SO2. Particularly, the forbidden SO emission line could be very weak as a result of SO is in such low concentrations and produced for less than a short while after being excited. Furthermore, the observations can solely be made when Io is in Jupiter’s shadow, when it’s simpler to see the glowing SO gases. When Io is in Jupiter’s shadow, the SO2 gasoline in Io’s environment freezes out onto its floor, leaving solely SO and newly emitted volcanic SO2 gasoline within the environment.

“These observations with Webb present for the primary time that this excited SO really did come from a volcano,” de Pater mentioned.

De Pater had made earlier observations of Io with the Keck Telescope in Hawaii and located low ranges of the forbidden SO emission over a lot of the moon, however she was unable to tie SO hotspots particularly to an energetic volcano. She suspects that a lot of this SO, in addition to the SO2 seen throughout an eclipse, is coming from so-called stealth volcanoes, which erupt gasoline however not mud, which might make them seen.

Twenty years in the past, de Pater and her workforce proposed that this excited state of SO might solely be produced in scorching volcanic vents, and that the tenuous environment allowed this state to stay round lengthy sufficient — a couple of seconds — to emit the forbidden line. Usually, excited states that produce this emission are shortly damped out by collisions with different molecules within the environment and by no means seen. Solely in elements of the environment the place the gasoline is sparse do such excited states final lengthy sufficient to emit forbidden strains. The greens and reds of Earth’s auroras are produced by forbidden transitions of oxygen within the tenuous higher environment.

“The hyperlink between SO and volcanoes ties in with a speculation we had in 2002 to elucidate how we might see SO emission in any respect,” she mentioned. “The one method we might clarify this emission is that if the SO is worked up within the volcanic vent at a temperature of 1500 Kelvin or so, and that it comes out on this excited state, loses its photon inside a couple of seconds, and that’s the emission we see. So these observations are the primary that truly present that that is the probably mechanism of why we see that SO.”

Webb will observe Io once more in August with NIRSpec. The upcoming statement and the sooner one, which befell on Nov. 15, 2022, have been taken when Io was within the shadow of Jupiter in order that gentle mirrored from the planet didn’t overwhelm the sunshine coming from Io.

De Pater famous, too, that the brightening of Loki Patera was according to the noticed interval of eruptions on the volcano, which brighten, on common, about each 500 Earth days, with the brightening lasting for a few months. She decided this as a result of it was not brilliant when she noticed the moon with Keck in August and September 2022, nor was it brilliant when one other astronomer noticed it from April by means of July 2022. Solely the JWST captured the occasion.

“The Webb observations confirmed that truly eruptions had began, and that it was a lot brighter than what we had seen in September,” she mentioned.

Whereas De Pater is primarily centered on the Jovian system — its rings, small moons and the bigger moons Ganymede and Io — she and different members of the early science workforce of some 80 astronomers are additionally utilizing JWST to check the planetary methods of Saturn, Uranus and Neptune.



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