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Io’s polar volcanic thermal emission supports magma ocean and asthenospheric tidal heating models

Presentation #103.02 in the session Fire and Ice: Io and Beyond (Oral Presentation)

Published onOct 23, 2023
Io’s polar volcanic thermal emission supports magma ocean and asthenospheric tidal heating models

The distribution of volcanic activity on Io is likely the result of tidally-induced internal heating. Models predict enhanced heat flow at Io’s poles if tidal heating is deep in the mantle, and at lower latitudes if heating is predominantly in the asthenosphere or a magma ocean is present. We must first understand the distribution and magnitude of Io’s tidal heating in order to determine the current position of Io in the evolving orbital resonance with Europa and Ganymede. However, previous missions did not adequately observe Io’s poles. The desired global measurements of volcanic thermal emission were made possible only when NASA’s Juno mission entered Jupiter polar orbit in 2016. We have created maps of 4.8 μm spectral radiance and the first global map of active hot spot thermal emission with increased polar sensitivity with spectral radiances from 266 active hot spots identified in Juno Jovian Infrared Auroral Mapper (JIRAM) data [1] from PJ05 (March 2017) through PJ43 (July 2022). We find 60% more volcanic spectral radiance per unit area at latitudes lower than 60° than at higher latitudes. These results are the opposite of those reported by [2]. Although the numbers of hot spots per unit area are not greatly different, polar volcanoes emit less energy at 4.8 μm than volcanoes at lower latitudes by a factor of more than two. Our results also show that average north polar volcano spectral radiance is more than twice that of south polar volcanoes, suggesting dichotomies in structure and volcanic advection between polar regions. Correlating total volcanic heat flow with model heat flow is a more robust method of ascertaining global heat flow pattern than counting hot spots in a given area. The strongest correlation between our thermal emission estimates and heat flow models is with the magma ocean model, a correlation slightly better than with the shallow tidal heating model. The weakest correlation is with the deep mantle heating model. Io’s anomalously warm poles are at odds with observed low volcanic thermal emission, an unexpected result. References: [1] Davies et al. (2023) Nature Astronomy, in revision. [2] Zambon et al. (2023) GRL, 50, e2022GL100597. © Caltech 2023.

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