Io in the Infrared: A New Paradigm from Juno’s Close Flybys

The Juno mission, through its JIRAM infrared instrument, has fundamentally reshaped our understanding of Io, transitioning our view of the moon from a collection of isolated hotspots to a world dominated by interconnected magmatic systems. This presentation synthesizes key findings from the 2023–2024 close flybys, which provided unprecedented spatial resolution of Io’s volcanic landscapes.

JIRAM observations have confirmed that lava lakes are the most ubiquitous volcanic feature on Io, typically characterized by a cooling central crust surrounded by a narrow "hot ring" of exposed lava. A critical shift in our understanding of Io’s energy budget has emerged: while these rings are the most prominent features in the M-band (5 µm), the vast majority of the total thermal power is actually emitted by the larger, low-temperature crusts. This implies that previous observations, insensitive to these cooler components, may have underestimated the contributions of lava lakes to  Io’s volcanic heat flow by up to an order of magnitude; we  identified crustal overturn in paterae as a primary cooling mechanism for the interior.

Central to this new perspective are the high-resolution observations of Loki Patera. JIRAM data allowed for the precise mapping of a resurfacing wave propagating at a constant 2–3 km/day. By modeling the thermal evolution of the crust, we find that the observed cooling rates are inconsistent with simple foundering or fracturing. Instead, we propose a model of intact subsidence, where magma percolates through a pre-existing fracture network, causing the crust to sink while fresh lava resurfaces the lake.

Finally, the detection of massive, synchronized eruptions—such as the December 2024 event in Illyrikon Regio which peaked at ~200 TW—provides the first direct evidence of physical connectivity between magma reservoirs separated by hundreds of kilometers. These findings suggest that Io’s subsurface is not a global magma ocean, but a complex, "sponge-like" network of interconnected magma chambers that define the most extreme thermal engine in the solar system.