NASA discovers the heat source of the moon Io, the most volcanic body in the Solar System

The moon Io, a satellite of Jupiter, is recognized as the most volcanic body in the Solar System, featuring a surface constantly reshaped by active volcanoes. Although scientists had measured the heat radiating from its surface for decades, what was happening beneath it remained a mystery. New observations, using data from NASA's Juno probe, allowed for the first time to measure temperatures below Io's surface.

How the probe got there

While infrared instruments assess surface temperature, Juno's Microwave Radiometer uses six antennas to detect microwaves at different wavelengths. Each antenna investigates a distinct depth, ranging from mere centimeters to tens of meters beneath the crust. The probe made approaches approximately 1,500 km from Io's surface on December 30, 2023, and again on February 3, 2024, enabling the first direct measurements of subterranean temperature.

Shannon Brown, the lead author of the study from NASA's Jet Propulsion Laboratory, reported that the instrument managed to measure Io's thermal emission at depths ranging from a few centimeters to tens of meters.

The findings indicated a temperature increase of over 22°C just a few meters below the surface, constituting a thermal gradient significantly steeper than solar heating alone could justify; this points to the heat coming from internal sources. Researchers identified two potential mechanisms for this heating. The first involves a continuous flow of heat through solid rock, quantified between 1 and 3 watts per square meter. While modest in isolation, this flow, when summed across the entire moon, represents an energy release up to 30 times greater than the Earth's average.

The second mechanism suggests that buried lava fields are slowly cooling beneath a hardened crust layer of about 9 to 10 meters. Such underground reservoirs could be present on approximately 10% of Io's surface at any given time.

What makes Io so volcanic

The primary cause of Io's volcanic activity lies in the phenomenon of tidal heating. Due to its slightly elliptical orbit around Jupiter, the giant planet's gravity exerts a constant force of traction and compression on the moon. This incessant deformation generates considerable amounts of internal heat. Scott Bolton, a co-investigator on Juno at the Southwest Research Institute, commented that Io offers a unique opportunity to understand the workings of tidal heating throughout the cosmos, a vital process that provides energy and heat to worlds located far from their host stars.

This same process may be responsible for nourishing subsurface oceans on other Solar System satellites, such as Europa and Ganymede, and also on planets orbiting distant stars.

A surprisingly smooth surface

Although Io is notorious for its prominent mountains and continuous eruptions, the Juno mission revealed another unexpected aspect: vast areas of the moon are considerably flatter than expected. According to Brown, away from mountainous formations, the surface resembles the Great Plains of North America. Furthermore, despite being a rocky body, the surface material has a very low density, comparable to volcanic ash or pumice, rather than solid rock.

This low-density characteristic on the surface may help explain how heat propagates through the upper layers of the moon.

The connection to Earth

The discoveries made on Io have implications that extend beyond the satellite. Bolton emphasized that the same type of microwave instrument could be applied in the future to the study of terrestrial volcanoes, allowing for the detection of subsurface temperature gradients and the revelation of processes that surface measurements cannot capture. Bolton concluded that the surprising fact of being able to observe beneath the surface of a rocky moon has important consequences for the investigation of Earth's volcanoes.

olhardigital.com.brJuly 22, 19:02

International group of astronomers discovers signs of a giant exomoon

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.

Methodology and Observations

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.

Classification and Challenges of the Discovery

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.

Comments from the Lead Scientist

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.

Future Research Steps

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.