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.”

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.

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.

Scientists from the Southwest Research Institute’s Center for Lunar Origin and Evolution (CLOE) have revealed new models of the Moon’s oldest and largest impact crater, the South Pole-Aitken (SPA) basin, providing fresh insights into the event and resulting material deposition on the lunar surface.

The SwRI team behind the new models, which is part of NASA’s Solar System Exploration Research Virtual Institute, said such details will help prepare future Artemis astronauts for what they could encounter during their upcoming missions.

Impact Study Reveals Details About Moon’s Oldest and Largest Crater

In a statement announcing the new models, Dr. William Bottke, director of CLOE and executive director of SwRI’s Science Directorate in Boulder, Colorado, said that the basin is an attractive potential target for future Artemis missions since it offers a “rare opportunity” to study an earlier era in the Moon’s history.

“The collision struck the lunar surface with such force that it may have excavated material from deep inside the Moon, including portions of the lunar mantle,” explained the co-author of the impact study detailing the new research.

Although previous studies have modeled impacts that may have caused the Moon’s oldest and largest crater, the team’s new effort has revealed new evidence about the composition of the impacting object and its likely direction and angle.

“Our simulation produces the right shape and nature of the impact basin,” explained the impact study’s lead author, Dr. Shigeru Wakita of Purdue University. “It also tells us about the projectile that created it and the direction of the impact.”

For example, the new model suggests that the object was not a single, uniform object. Instead, the team found that the impactor was likely a “differentiated” object, such as a protoplanet or asteroid, composed of rock and surrounded by an iron core. The models also found that the object approached from the north “at a low angle” before impacting the Moon’s surface on a southward trajectory.

According to the impact study authors, the impact excavated a deep, “asymmetric” cavity and generated enough energy to melt the rock within the crater’s central basin, resulting in the SPA basin’s elongated, tapered shape. Their models also indicated that the object’s lunar collision “lofted” large amounts of material into the air. Critically, their models also revealed that material from both the lunar crust and mantle was likely ejected before ultimately settling back onto the basin floor.

Exploring Gravity’s Role and the Possibility of ‘Valuable’ Mantle in the Impact Ejecta

To help potential future lunar astronauts, including members of NASA’s Artemis mission, target the most scientifically valuable lunar samples, a second companion study explored the effects of gravity on ejecta distribution beneath and around the impact basin. According to the team behind that effort, their effort involved direct comparisons of high-resolution gravity data with models. Specifically, they wanted to determine if pieces of the Moon’s crust and mantle were included in the ejection.

After comparing the two, the authors of the second study determined that the SPA basin “likely contains substantial amounts of mantle-derived rocks” both within its interior and mixed into the wider ejecta blanket surrounding the basin. Also critical for future missions, the analysis revealed that this material was not all scattered during the initial impact.

Instead, the new models showed that subsequent, smaller impacts appear to have “excavated” these underlying mantle deposits. As a result, the team suggests that there is likely enough material on the surface of the Moon’s oldest and largest crater “where it could be readily sampled by robotic rovers or astronauts during future missions.”

The Studies Provide Future Lunar Missions with a “Powerful Roadmap”

When discussing the significance of the gravity study’s findings, lead author Dr. Gabriel Gowman of the University of Arizona said that before now, the “precise distribution” of lunar mantle material on the Moon’s surface “has been a big unknown.” For example, some previous theories suggested that the deepest ejecta might be found only in parts of the basin that are not currently included in planned Artemis missions.

Now, the team’s new models suggest that the impact that formed the SPA basin “ejected enough deep material to form a significant deposit that should still be accessible today.” More importantly, Dr. Gowman added, some of that scientifically valuable mantle material “at a trace level” may exist in regions currently under consideration for upcoming Artemis landings. Taken together, Bottke said, the two studies can provide a “powerful roadmap” for future lunar scientific missions to the Moon’s oldest and largest crater.

“It tells us not just how SPA formed, but where to look for the rocks that can answer some of our biggest questions about the Moon’s origin and evolution,” the researcher explained.

The Impact study “A southward differentiated impactor forms the tapered shape of the South Pole-Aitken impact basin on the Moon” was published in Science Advances.

The gravity study “Gravity Mapping of Lunar Mantle Material in South Pole-Aitken Basin Ejecta” was published in the Journal of Geophysical Research: Planets.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

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