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Received — 25 July 2026 ⏭

What lurks beneath the volcanoes of Jupiter's moon Io? NASA's Juno probe just took a peek

✇Space
24 July 2026 at 17:00

Scientists have measured temperatures beneath the surface of Jupiter's volcanic moon Io, offering the first-ever glimpse of the hidden heat driving the most volcanically active world in the solar system.

During close flybys of Io in late 2023 and early 2024, NASA's Juno spacecraft turned its Microwave Radiometer (MWR) instrument toward the moon, probing roughly six to 20 feet (two to six meters) beneath its surface. Originally designed to peer through Jupiter's thick clouds, the instrument instead revealed a powerful new way to study how heat moves through planetary crusts, according to a statement from the space agency.

"The surprising discovery that we could see below a rocky moon's surface has important implications for studying Earth's volcanoes," Scott Bolton, coauthor of the study and Juno's principal investigator, said in the statement. "Juno has taught us that if we look with an MWR-type instrument near a volcano on Earth, we might see a similar signature in the subsurface temperature gradient, providing new information on how terrestrial volcanoes work."

Until now, researchers had relied almost entirely on infrared observations, which detect only the temperature of Io's surface. By probing several feet underground, Juno has revealed how heat moves through the moon's crust for the first time.

The measurements showed temperatures rising by more than 40 degrees Fahrenheit (22 degrees Celsius) just a few feet below the surface — far more than sunlight alone could explain. Juno's subsurface heat map also revealed localized regions of elevated heat, with temperatures measuring between 18 and 36 degrees F (10 to 20 degrees C) warmer than the surrounding terrain, according to the statement.

Juno's observations uncovered another surprise, too. Despite being known for its towering mountains and active volcanoes, much of Io's surface appears remarkably smooth and composed of unusually low-density material. Researchers think the moon is blanketed by porous layers of volcanic ash, sulfur frost and other eruptive debris that continually resurface Io, burying older terrain beneath fresh deposits.

Scientists think the heat detected beneath Io's surface could be rising steadily from the moon's molten interior through a conductive crust or coming from pockets of cooling lava flows trapped just below the surface. Either way, the data provide the clearest picture yet of how Io transports heat from its interior.

Unlike Earth, where volcanism is driven largely by heat from radioactive decay, Io is continuously stretched and squeezed by Jupiter's immense gravity as it orbits the giant planet. This constant tidal flexing generates enormous amounts of internal heat, fueling hundreds of active volcanoes and making Io the most volcanically active object in the solar system. By improving scientists' understanding of how heat and magma move beneath a planet's surface before eruptions, the same microwave techniques used by Juno could one day help researchers better monitor Earth's volcanoes and improve eruption forecasting.

"Io provides a unique window into learning how tidal heating works throughout the cosmos, a fundamental process that provides energy and heat to worlds that are far from their parent star," Bolton said in the statement. "This process can not only create the most volcanic body in the solar system, in the case of Io, but also fuels the subsurface oceans on the moons of giant planets, such as Europa and Ganymede. Up until this point we could only observe the heat escaping at the surface or through eruptions. Now we can characterize how the heat is moving from the interior toward the surface."

Because Io is an extreme example of volcanic activity, it serves as a natural laboratory for studying how heat moves through planetary crusts. Those insights could help scientists better understand ancient volcanism on Mars, Venus, and Earth's moon, whose landscapes were shaped by massive eruptions billions of years ago.

The technique could also aid the search for life elsewhere. While Io itself is far too hostile to support life, microwave instruments can also probe beneath icy surfaces. Juno has already used the same instrument to study Jupiter's moons Europa and Ganymede, where scientists believe vast oceans lie hidden beneath thick shells of ice. Understanding how heat moves through those crusts is key to determining whether they could harbor environments suitable for life as we know it.

Their findings were published July 22 in the Journal of Geophysical Research: Planets.

Rare “Super-Jupiter” Discovered on an Extraordinary 180-Day Orbit

✇SciTechDaily
By: Queen's University Belfast
24 July 2026 at 12:54
NGTS 38 bScientists discovered a rare planet larger than Jupiter orbiting a distant star once every 180 days. A planet nearly five times as massive as Jupiter circles a distant star once every 180 days. Known as NGTS-38 b, it is an exoplanet, meaning a world that orbits a star outside our solar system. NGTS-38 b is [...]

“Everywhere We Looked, We Found the Temperature Rising”: NASA Identifies a “Surprise” Heat Signature Below the Surface of Jupiter’s Moon Io

✇The Debrief
By: Christopher Plain
23 July 2026 at 13:51

NASA’s Juno mission scientists have reported the first successful temperature measurements below the surface of Jupiter’s moon Io, including indications of significant heating within the moon’s shallow subsurface.

Collected during a pair of close flybys of the Solar System’s most volcanically active world, the Juno mission measurements were described as a complete “surprise” since the instrument was designed for a different purpose.

“[The readings] break new observational ground for both fiery and icy worlds beyond our planet,” the team said.

MWR Instrument Designed to Probe Jupiter’s Atmosphere Provides Double Duty

Due to the extreme gravitational pull of its host planet, Jupiter, Io is repeatedly stretched and pulled as its slightly elliptical orbit carries it around the massive gas giant. This repeated motion generates a tremendous amount of heat, which the scientists note is “many times greater” than the same type of heat generated on Earth.

However, a detailed understanding of this process has remained elusive, as the only data on the moon’s inner heat came from infrared telescope observations. The team notes this data is limited to the temperature of Io’s upper rocky surface layer.

Conversely, Juno is equipped with an instrument called the Microwave Radiometer (MWR). According to the team’s statement announcing the successful subsurface temperature detection, Juno’s Microwave Radiometer was custom designed by Scott Bolton, the mission’s principal investigator at Southwest Research Institute in San Antonio and a co-author of the study detailing the team’s findings, to “peer beneath Jupiter’s top clouds” for a closer look at the gas giant’s complex atmosphere.

“The MWR’s six microwave antennas serve as a single instrument, simultaneously detecting microwaves at a wide range of wavelengths, from about half an inch to 20 inches (1.3 to 51 centimeters),” the team explains.

“Everywhere We Looked, We Found the Temperature Rising”

Bolton said the team’s novel approach allowed the instrument to observe wavelengths from different depths, “providing a new way to characterize the deep atmosphere of giant planets and the subsurface crusts of icy and rocky moons.” This included observations of Jupiter’s other ‘Galilean’ moons, Ganymede and Europa.

“At Ganymede and Europa, we explored tens of miles below the surface, assuming their ice shells were mostly pure water,” the mission scientists explained.

However, Bolton added, using the instrument to successfully probe into Io’s volcanic rock “was an unexpected discovery.”

Io
This map represents data captured by the Microwave Radiometer instrument aboard NASA’s Juno, indicating heat rising from just beneath the surface of Jupiter’s moon Io. The colors illustrate a distinct temperature gradient across the moon, with the most extreme, localized heat output in red. Image Credit: NASA/JPL-Caltech/SwRI/USGS.

The feat was accomplished during a pair of flybys on December 30, 2023, and February 3, 2024, where Juno came within roughly 930 miles (1,500 km) of Io’s surface. Shannon Brown, the paper’s lead author at NASA’s Jet Propulsion Laboratory in Southern California, said that during these flybys the MWR instrument measured the moon’s thermal emission “at depths ranging from a few inches down to tens of feet.”

“Everywhere we looked, we found the temperature rising by more than 40 degrees Fahrenheit just several feet into the surface — a gradient far steeper than solar heating alone can explain,” Brown said.

Jupiter's moon Io
This graphic illustrates the areas of Io sampled by the Microwave Radiometer instrument aboard NASA’s Juno spacecraft during two close flybys of the Jovian moon. Image Credit: NASA/JPL-Caltech/SwRI/USGS.

Although more information is likely needed to make a conclusive determination, the team said that the data suggests two possible explanations for the readings. The first option is heat rising steadily through what the team termed a “conductive crust.”

“While this background heat flow — measured at 1 to 3 watts per square meter — is relatively gentle on a local scale (roughly equivalent to a small nightlight glowing under every square yard), across the entire moon it represents a release of energy up to 30 times Earth’s average,” they explained.

Another possibility proposed by the joint research team suggested that the heat signal detected by Juno’s MWR could be coming from cooling lava flows covered by 30 to 35 feet (9 to 11 meters) of solidified crust that cover approximately 10% of Io’s surface “at any given time.”

A Similar Instrument Could be Used to Scan Earth

When discussing the implications of the team’s findings, Bolton said the “surprising” ability to see below Io’s surface “has important implications for studying Earth’s volcanoes.” He also noted that if scientists used a similar instrument to measure areas on Earth near volcanoes, they might see a similar heat signature in the planet’s subsurface temperature gradient, “providing new information on how terrestrial volcanoes work.”

“Io provides a unique window into learning how tidal heating works throughout the cosmos, a fundamental process that provides energy and heat to worlds that are far from their parent star,” Bolton explained. “This process can not only create the most volcanic body in the solar system, in the case of Io, but also fuels the subsurface oceans on the moons of giant planets, such as Europa and Ganymede.”

“Up until this point, we could only observe the heat escaping at the surface or through eruptions,” the mission scientists added. “Now we can characterize how the heat is moving from the interior toward the surface.”

NASA has additional information about Juno available at the mission’s official webpage.

Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org.

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