NASA’s Juno spacecraft is poised to make the closest flyby of Io, Jupiter’s volcanic moon, since the mission began in 2011. The encounter is scheduled for December 30, and the flyby will bring Juno within 1.5 thousand kilometers of Io’s turbulent surface, enabling high-resolution imaging and in-depth temperature mapping with its suite of cameras and sensors. This visit marks a milestone for a mission that has traveled across the solar system and continues to reveal new details about Io’s geology and atmospheric conditions, with data expected to sharpen our understanding of how a moon can stay so geologically active.
Juno reached Jupiter’s system in 2016 after a voyage covering roughly 2.8 billion kilometers. Over the past eight years, the spacecraft has completed 56 orbits around the gas giant, gathering a treasure trove of measurements about Jupiter’s magnetosphere, gravitational field, rings, and moons. Io stands out as the most volcanically vigorous body in the solar system, its surface peppered with hundreds of active vents that spew lava high into the moon’s shadowed, tenuous atmosphere. Scientists attribute this extraordinary activity to the immense tidal forces exerted by Jupiter and the other Galilean moons, including Ganymede, Callisto, and Europa, which stretch Io’s crust as it orbits the planet.
The relentless pull from Jupiter flexes Io’s interior, raising the moon’s surface by as much as 100 meters in places and likely driving ongoing volcanic eruptions. This tidal heating keeps Io’s interior partially molten, fueling continuous volcanic activity that reshapes the surface on timescales much shorter than those seen on other moons. The Juno flyby will help researchers probe how this energy is generated and distributed, shedding light on the moon’s internal structure and thermal dynamics.
With Juno present, planetary scientists hope to determine whether Io harbors a subsurface ocean of liquid magma or other exotic molten reservoirs beneath its crust. During the closest approach, the spacecraft’s instruments will be activated to capture a full spectrum of data, including surface temperatures, infrared emissions, and high-resolution imagery, while also pinpointing active volcanoes and mapping their distribution. This data will contribute to broader questions about tidal heating, planetary geophysics, and the evolution of rocky moons in strong gravitational fields, offering comparative insights for the many icy and rocky worlds studied by researchers in North America and beyond.
Looking ahead, the Juno mission is planned to continue operating through 2025, with the possibility of graceful completion as the probe eventually re-enters Jupiter’s atmosphere. The ongoing observations promise to enhance our comprehension of Jupiter’s system as a whole and Io’s unique place within it, adding new layers to the science of planetary volcanism and celestial mechanics that excite space enthusiasts and researchers across the United States and Canada alike.
This mission is part of a broader cadence of exciting space science in 2024, highlighting the ongoing human quest to understand moons, planets, and the forces that shape them. The Juno team’s work continues to fuel curiosity about how tidal interactions sculpt worlds and what those processes can tell us about the history and dynamics of our own solar neighborhood. These results will be shared through NASA’s Jet Propulsion Laboratory updates and peer-reviewed publications, providing a clear view of Io’s fiery activity and its implications for planetary science.