Channelized Thermal Emission, Promethean-Type Jets and Surface Changes on Io From Juno Stellar Reference Unit Imagery

Abstract

During Juno's close flybys of Io in 2023 and 2024, its low-light sensitive Stellar Reference Unit (SRU) was used to conduct a high-resolution visible wavelength (450–1,100 nm) imaging campaign under Jupiter-shine illumination. The SRU acquired Juno's highest resolution image of Io's surface (895–1,230 m/pixel) in December 2023 at a high Jupiter-shine phase angle of ∼110°. The image reveals structural changes in Zal Patera since Galileo (1999–2000) and multiple forms of active volcanism within the Zal Montes-Patera complex, including Promethean-type jets at the flow fronts of a new Zal Patera flow branch. The SRU's sensitivity at redder wavelengths enabled the detection of thermal emission from an active lava channel to the west of South Zal Mons. An additional emission signature is seen at the base of a vertical mountain fracture on the western flank of South Zal Mons, suggestive of a tectonically influenced source vent. Indeed, the SRU's observations in this region suggest a close relationship between mountains and volcanism on Io. The SRU data also provide the first high-resolution view of the geomorphology of the eruptive center Tonatiuh, revealing it to be a compound Promethean-style flow field. SRU imagery from subsequent flybys in February and April 2024 suggest high volcanic activity in the Lei-zi Fluctus region and show increased expansion of the large Masubi flow field in Io's southern hemisphere. Now containing ∼1,600 km of lava flows, Masubi is the longest currently active flow field in the solar system.