The most faithful portrait of Io, Jupiter's innermost moon

NASA’s Juno spacecraft has captured the most detailed portrait yet of Io, Jupiter’s innermost moon and the most volcanically active body in the entire solar system. The findings, published in the Journal of Geophysical Research: Planets, reveal new insights into the moon's internal heat dynamics, offering potential implications for studying exoplanets beyond our solar system. The data comes from two close flybys of Io conducted by Juno in late 2023 and early 2024. During these encounters, the probe came within approximately 1,500 kilometers of Io’s surface, using its microwave radiometer instrument to peer beneath the moon’s crust. This device, equipped with six antennas of varying sizes mounted on the sides of the spacecraft, operates across a wide range of wavelengths, between 1.3 and 51 centimeters, to penetrate Io’s dense atmosphere and gather subsurface information. According to the study led by researchers at NASA’s Jet Propulsion Laboratory, Juno detected a temperature increase of more than four degrees Celsius just a few centimeters below Io’s surface. This rapid rise in temperature suggests ongoing geological activity beneath the moon’s rocky exterior. Scientists have proposed two possible explanations for this phenomenon. One hypothesis posits that Io possesses a crust that allows heat to continuously rise toward the surface. Another theory speculates the presence of underground lava flows trapped between nine and eleven meters deep, affecting roughly 10 percent of Io’s surface at any given time. Juno, launched in August 2011, has been orbiting Jupiter since July 2016. Its primary mission involves studying the planet’s magnetic field, atmospheric composition, and interior structure. However, the spacecraft’s instruments have proven invaluable for observing Jupiter’s moons, including Io, Europa, Ganymede, and Callisto. The ability of Juno’s microwave radiometer to detect subsurface temperatures marks a significant advancement in planetary science, enabling scientists to investigate geothermal processes on celestial bodies previously thought too distant or inhospitable for such observations. Io’s extreme volcanic activity is driven by tidal heating caused by gravitational interactions with Jupiter and its other moons. As Io orbits Jupiter, the immense gravitational forces exerted by the gas giant and its satellites create friction within the moon’s interior, generating substantial heat. This process results in frequent eruptions, making Io one of the most dynamic objects in the solar system. Previous missions, such as Galileo and Voyager, had observed Io’s surface features and volcanic plumes, but none had measured subsurface temperatures directly until now. The research team, led by Shannon Brown of JPL, emphasized the importance of understanding how heat moves through Io’s crust. Their findings could help refine models of similar geological processes on other planets and moons, particularly those with active tectonic systems. By analyzing the thermal signatures collected during Juno’s flybys, scientists hope to gain a better understanding of how internal heat influences surface features and volcanic activity on celestial bodies throughout the solar system. The study was published in the Journal of Geophysical Research: Planets after undergoing peer review. Researchers plan to continue analyzing data from Juno’s upcoming flybys of Io, aiming to build a more comprehensive picture of the moon’s internal structure and thermal behavior. Future missions targeting exoplanets may benefit from the techniques developed during this research, allowing for deeper exploration of planetary interiors even in distant star systems.