NASA's Juno measures heat beneath Jupiter's moon Io for first time

First Direct Look Beneath Io's Crust

NASA's Juno spacecraft has achieved a historic first: probing beneath the surface of Jupiter's volcanic moon Io. For decades, scientists have studied Io's dramatic eruptions from afar, but the moon's interior remained a mystery. Now, for the first time, Juno has delivered direct temperature measurements from just below Io's fiery crust.

The announcement came from a Southwest Research Institute (SwRI) scientist, who revealed the breakthrough findings. The data shows temperatures surging in the shallow subsurface, offering an unprecedented glimpse into the internal workings of the most volcanically active world in our solar system.

A Volcanic World Like No Other

Io is a hellish landscape, dotted with hundreds of active volcanoes that spew lava fountains and plumes reaching hundreds of kilometres into space. Its intense volcanic activity is driven by tidal flexing — the gravitational pull from Jupiter and its neighbouring moons stretches and squeezes the satellite, generating enormous internal heat.

Until now, scientists could only infer what lay beneath Io's surface by observing its surface eruptions and modelling its interior. The Juno spacecraft's latest pass has changed that, capturing thermal data that reveals the heat distribution just below the crust. The measurements suggest that temperatures are rising sharply in the shallow subsurface, far more than previous models predicted.

What the New Data Reveals

The findings indicate that the heat beneath Io's surface is not uniformly distributed. Instead, there are pockets of intense warmth, likely linked to the magma plumbing system that feeds the moon's many volcanoes. This suggests that Io's subsurface is a complex network of molten rock channels, rather than a simple, uniformly heated layer.

For planetary scientists, this is a major step forward. Understanding how heat moves through Io's interior can help explain not just Io itself, but also the processes that shaped other rocky bodies in the early solar system. The moon's volcanic activity is a natural laboratory for studying extreme geological processes.

How Juno Made the Measurement

Juno, which has been orbiting Jupiter since 2016, has been making close flybys of Io as part of its extended mission. During a recent pass, the spacecraft used its instruments to sense thermal radiation coming from the moon's surface and subsurface. By analysing the wavelengths and intensity of this radiation, scientists could separate the surface heat from the deeper heat signature.

This is the first time such a direct measurement has been made beneath Io's surface. Earlier missions, including NASA's Galileo, provided valuable data about Io's volcanic activity, but none could penetrate the surface layer to gauge internal temperatures.

Implications for Future Missions

The discovery has significant implications for the study of planetary interiors. It demonstrates that spacecraft can effectively peer beneath the surfaces of other worlds using thermal sensing techniques. This could inform future missions to other volcanic or geologically active bodies, such as Saturn's moon Enceladus or Jupiter's Europa.

For Io, the new data raises fresh questions. How deep do these hot zones extend? Are they connected to a global magma ocean, or are they isolated pockets? Scientists will need more flybys and additional data to build a complete picture of the moon's internal structure.

The Juno mission continues to exceed expectations, delivering insights that were not part of its original science goals. As the spacecraft makes more close approaches to Io, researchers hope to refine their models and perhaps even map the subsurface heat distribution in greater detail.

What remains to be seen is whether these temperature measurements will lead to a revised understanding of tidal heating — and whether similar processes could be at work on other ocean worlds in the outer solar system.