With New, Sharper Optics, Arizona Telescope Captures Rare Images of Jupiter’s Moon Io

Large Binocular Telescope's observations of eruptions on volcanically active moon rival those from space

Since 1979, when Jupiter’s moon Io was found to be pockmarked with volcanoes, astronomers and volcanologists have been excited by what the reddish satellite could tell us about the evolution of the Jovian system and Earth’s early volcanic history. Yet, studies of eruptions and lava flows on Io have been hampered by fuzzy images from Earth-bound and space-borne telescopes and far too few closeups from flyby spacecraft.

A sharp new camera recently installed on a telescope in Arizona could remedy that.

A team of astronomers and engineers will publish next week in the journal Geophysical Research Letters the highest resolution optical images of Io ever taken from Earth — images sharp enough to discern volcanoes so close to one another that the debris from their eruptions overlap.

Taken by the Large Binocular Telescope (LBT) on Mount Graham in Arizona, the images were made possible by a new high-contrast optical imaging instrument, dubbed SHARK-VIS, and the telescope’s adaptive optics system, which compensates for the blurring induced by atmospheric turbulence.

The images reveal surface features as small as 50 miles across, a spatial resolution that until now had been achievable only with spacecraft sent to Jupiter, such as the two Voyager spacecraft in 1979, the Galileo mission, which ended in 2003, and Juno, which has been orbiting Jupiter since 2016. The resolution is equivalent to taking a picture of a dime-sized object from 100 miles away, according to the research team. The images are two to three times better than could be obtained through the Hubble Space Telescope.

“The visible light images are really incredible,” said Imke de Pater, a professor emerita of astronomy and of earth and planetary science at the University of California, Berkeley, who helped interpret the images with Ashley Davies, a principal scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and Katherine de Kleer, assistant professor at the California Institute of Technology.

De Pater has been observing Io for decades, mostly using ground-based infrared telescopes, such as the Keck Observatory and Gemini Observatory in Hawaii, and radio telescopes like the Atacama Large (sub)Millimeter Array (ALMA) in Chile. Infrared observations capture hot features, such as lava flows, but are inherently lower resolution. Most recently, she analyzed infrared images from NASA’s newest observatory, the James Webb Space Telescope (JWST).

“With Keck and Gemini, it’s all in the infrared,” she said. “While we do see some surface features, when you image the satellite in visible light, you can really see images similar to what Voyager and Galileo have obtained. With these visible-light images, you can look at the landscapes and topography.”

Her hope is to combine optical images from the LBT with infrared observations to correlate glowing hot magma with visible features, such as lava flows and colorful deposits created by fallout from volcanic plumes.

“I hope we can do simultaneous observations at some point in the infrared and visible to see the hot magma and then the effect of that on the surface,” she said. “Sharper images at visible wavelengths like those provided by SHARK-VIS and LBT are essential to identify both locations of eruptions and surface changes not detectable in the infrared, such as new plume deposits.”

Pele and Pillan Patera, dueling volcanoes

According to the paper’s first author, Al Conrad, an associate staff scientist at the Large Binocular Telescope Observatory, the eruptions on Io — the most volcanically active body in the solar system — dwarf their contemporaries on Earth. Studies like this one will help researchers understand why some worlds in the solar system are volcanic, but not others, he said, and may someday shed light on volcanic worlds in exoplanet systems around nearby stars.

“Io, therefore, presents a unique opportunity to learn about the mighty eruptions that helped shape the surfaces of Earth and the moon in their distant pasts,” Conrad said.

Slightly larger than Earth’s moon, Io is the innermost of Jupiter’s Galilean moons, which in addition to Io include Europa, Ganymede and Callisto. Locked in a gravitational “tug of war” among Jupiter, Europa and Ganymede, Io is constantly being squeezed, leading to frictional heat buildup in its interior — believed to be the cause for its sustained and widespread volcanic activity.

By monitoring the eruptions on Io’s surface, scientists hope to gain insights into the heat-driven movement of material underneath the moon’s surface, its internal structure and, ultimately, on the tidal heating mechanism responsible for Io’s intense volcanism.

Davies said that the new image taken by SHARK-VIS is so rich in detail that it has allowed the team to identify a major resurfacing event in which the plume deposit around a prominent volcano known as Pele, located in Io’s southern hemisphere close to the equator, is being covered by eruption deposits from Pillan Patera, a neighboring volcano. A similar eruption sequence was observed by NASA’s Galileo spacecraft, which explored the Jupiter system between 1995 and 2003.

“We interpret the changes as dark lava deposits and white sulfur dioxide deposits originating from an eruption at Pillan Patera that partially cover Pele’s red, sulfur-rich plume deposit,” Davies said. “Before SHARK-VIS, such resurfacing events were impossible to observe from Earth.”

According to de Pater, Pele seems to erupt continuously, sending plumes of volcanic gases some 300 kilometers above Io’s surface — high enough to have been imaged by Voyager, Galileo and Hubble. The gases in the plume, which emerge from a lava lake, freeze and settle on the surface as a prominent, broad, reddish, sulfur-rich ring.

Pillan Patera, on the other hand, seems to erupt episodically, leaving emplaced lava surrounded by a white ring of frozen sulfur dioxide (SO2). The new images show the white deposits obscuring Pele’s reddish deposits, though likely for only a brief period. Photos of Io taken by Juno in April showed a nearly complete orange ring, with perhaps a hint of paler red where Pillan’s deposits had been.

“It’s kind of a competition between the Pillan eruption and the Pele eruption, how much and how fast each deposits,” she said. “As soon as Pillan completely stops, then it will be covered up again by Pele’s red deposits.”

SHARK-VIS was built by the Italian National Institute for Astrophysics at the Rome Astronomical Observatory and is managed by a team led by principal investigator Fernando Pedichini, assisted by project manager Roberto Piazzesi. In 2023, it was installed at the LBT, together with its complementary near-infrared instrument SHARK-NIR, to fully take advantage of the telescope’s outstanding adaptive optics system. The instrument houses a fast, ultra-low noise camera that allows it to observe the sky in “fast imaging” mode, capturing slow-motion footage that freezes the optical distortions caused by atmospheric turbulence, and to post-process data to an unprecedented sharpness.

SHARK-VIS instrument scientist Simone Antoniucci said he anticipates new observations to be made on objects throughout the solar system.

“The keen vision of SHARK-VIS is particularly suited to observing the surfaces of many solar system bodies — not only the moons of giant planets, but also asteroids,” he said. “We have already observed some of those, with the data currently being analyzed, and are planning to observe more.”

The LBT is part of Mount Graham International Observatory, a division of the University of Arizona’s Steward Observatory.

Related Information

• Observation of Io’s Resurfacing via Plume Deposition Using Ground‐Based Adaptive Optics at Visible Wavelengths With LBT SHARK‐VIS (GRL)
• University of Arizona press release
• James Webb Space Telescope sees Jupiter moons in a new light (2023)
• Active volcanoes feed Io’s sulfurous atmosphere (2020)
• Long-term, hi-res tracking of eruptions on Jupiter’s moon Io (2016)
• Imke de Pater’s website