The NASA Juno mission has successfully identified evidence of localized heating beneath the surface of Io, a moon of Jupiter known for its vigorous volcanic activity. These measurements were collected during flybys conducted in late 2023 and early 2024.
The study utilized the spacecraft's microwave radiometer to examine the moon's subsurface layers, reaching depths of several meters below the ground. The obtained data detail how Io's internal heat propagates through the crust before reaching the surface.
The research was published last Wednesday, the 22nd, in the journal JGR Planets. This discovery has the potential to alter the scientific methodology used in analyzing volcanoes on other celestial bodies and may assist in investigations into terrestrial volcanism. Furthermore, the work expands the understanding of icy moons that potentially harbor internal oceans.
During the close passes executed by the Juno probe on December 30, 2023, and February 3, 2024, the spacecraft's microwave instrument was focused on Io. Although this instrument was initially designed to monitor Jupiter's dense clouds, it demonstrated the capability to investigate temperatures below the terrain of this volcanic moon.
Previously, scientists relied mainly on infrared observations, which could only register visible heat on the surface. The new technique allowed for the analysis of thermal distribution at depths ranging from two to six meters. Readings indicated a temperature increase exceeding 22 degrees Celsius just a few meters below the surface, and the mapping also signaled hotter regions than their surroundings, showing variations of 10 to 20 degrees Celsius.
Scott Bolton, lead researcher for the Juno mission and co-author of the study, commented that this discovery suggests that a similar technology could provide new knowledge about volcanoes on Earth. In a statement to NASA, Bolton stated: 'If we look with an MWR-type instrument near a volcano on Earth, we might see a similar signature in the subterranean temperature gradient, providing new information on how terrestrial volcanoes function.'
The analysis of Io's interior also revealed a surprising aspect. Despite having numerous active volcanoes and large mountains, much of the moon's surface appears relatively uniform and composed of low-density materials. Experts suggest that this characteristic may be associated with the continuous renewal of the soil caused by eruptions, where layers of volcanic ash, sulfur ice, and other expelled debris cover older terrains, resulting in a constantly changing surface.
Unlike Earth, where much of the volcanic activity derives from heat generated by radioactive decay, Io obtains its energy through another process. Jupiter's immense gravitational force causes constant deformations in the moon as it orbits the planet. This stretching and compressing motion, called tidal heating, generates heat in the satellite's interior, driving its intense volcanic activity, making Io the most volcanically active body known in the Solar System.
Researchers speculate that the heat detected beneath the surface may be rising directly from the moon's molten core through the crust or originating from pockets of lava trapped near the ground as they cool. According to Bolton, observing Io aids in understanding how this heating mechanism operates in various space scenarios. He stated: 'Io offers a unique window to learn how tidal heating works across the cosmos, a fundamental process that provides energy and heat to worlds far from their stars.'
The same methodology can be applied to studying other elements of the Solar System. Since the instrument was also used to investigate Europa and Ganymede, moons of Jupiter that may contain oceans under layers of ice, the results help understand thermal movement in subterranean environments. Even though it is considered uninhabitable, understanding Io's internal dynamics can support research on ancient volcanism on Mars, Venus, and Earth's Moon.
An international group of astronomers has recorded signs of a potential natural satellite outside the Solar System. This object is located in a system consisting of a star, a brown dwarf, and a body whose mass approaches that of Jupiter.
The study showed that the celestial body orbits the brown dwarf CD-35 2722 B, which, in turn, moves around a star with approximately half the mass of the Sun. Observations were conducted from October 2023 to February 2026 using the Very Large Telescope (VLT) located in Chile.
The potential exomoon was not observed directly. Its existence was established by changes in the movement of the brown dwarf caused by the gravitational pull of this object. Researchers determined that the orbital period of this body is about 170 days.
Confirmation of this discovery still requires additional measurements. Despite its similarity to moons, this object possesses significantly greater mass than known Solar System satellites and orbits a brown dwarf, not a planet. Therefore, researchers initially used the term exomoon to describe the body orbiting another object outside the Solar System, without defining its classification as a moon or a planet.
The main difficulty lies in the unusual structure of this system. In our Solar System, moons usually orbit planets, while planets orbit stars. The new configuration includes a moon-like body orbiting a brown dwarf—an object situated between the category of a giant planet and a star.
Kevin Hoy, the lead author of the study and a graduate student at Universidad Diego Portales in Chile, stated in an interview with g1 that the object is difficult to define because scientists are 'truly expanding the boundaries of the words we have invented to describe the Solar System, trying to apply them to a system that is completely unlike ours.'
According to the researcher, the detection of the signal was an important moment for the team, especially because the predictions made based on preliminary data were confirmed by subsequent observations. Hoy specified that the new recordings demonstrated behavior consistent with the model created by the scientists.
The brown dwarf CD-35 2722 B has a mass approximately 37 times that of Jupiter. The associated object has dimensions allowing for comparison with a giant planet, although its position in the system allows it to be considered a moon. The team reached this conclusion by tracking small fluctuations in the displacement of the brown dwarf, which were attributed to the gravitational influence of the body in orbit, thus revealing a recurring pattern over time.
Currently, astronomers plan to collect additional data for a more accurate calculation of the possible satellite's mass and confirmation of its trajectory. One planned strategy is the direct measurement of the displacement caused by the object on the brown dwarf. This discovery may expand the search for similar bodies in distant systems. As astronomical instruments develop, the same methodology can help identify smaller exomoons that are more similar in characteristics to satellites found in the Solar System. Hoy believes that the research may also stimulate a review of the criteria for classifying celestial bodies, as such cases could provoke a broader discussion about the meaning of terms like exomoon and exoplanet.
