Io’s polar volcanic thermal emission indicative of magma ocean and shallow tidal heating models

Abstract

The distribution of Io’s volcanic activity probably reflects the position and magnitude of internal tidal heating, but full mapping of the moon has not been possible due to a lack of polar coverage. Here we use new observations of Io’s polar regions by the Juno spacecraft Jovian Infrared Auroral Mapper to complete near-infrared coverage, revealing the global distribution and magnitude of thermal emission from Io’s currently erupting volcanoes. We show that the distribution of volcanic heat flow from 266 active hot spots is consistent with the presence of a global magma ocean and/or shallow asthenospheric heating. We find that Io’s polar volcanoes are less energetic but approximately the same in number per unit area than those at lower latitudes. We also find that volcanic heat flow in the north polar cap is greater than that in the south. The low volcanic advection seen at Io’s poles is therefore at odds with measurements of background temperature, showing that Io’s poles are anomalously warm. We suggest that the differences in volcanic thermal emission from Io’s poles compared with those at lower latitudes are indicative of lithospheric dichotomies that inhibit volcanic advection towards Io’s poles, particularly in the south polar region.

Near Infrared Spectral Radiance at Multiple Wavelengths From Io's Volcanoes 1: The Low Spatial Resolution Night‐Time Galileo NIMS Data Set

“…The Pillan eruption of 1997, observed by Galileo instruments, has been well-documented (Davies et al, 2001;Keszthelyi et al, 2001;Williams et al, 2001), with thermal emission and visible data interpreted as a voluminous eruption, likely involving a period of lava fountaining, that emplaced ≈56 km 3 of lava that covered 5,600 km 2 of Io's surface in less than 6 months. A number of subsequent eruptions at Pillan have been identified in ground-based telescope data (Cantrall et al, 2018;de Kleer et al, 2019a;de Pater, Davies, & Marchis, 2016), and in observations made by the Jupiter Infrared Auroral Mapper (JIRAM) on the Juno spacecraft (Davies, Perry, et al, 2023;Zambon et al, 2023). The thermal behavior of activity at Pillan suggests a cycle of lava discharge followed by a dormant period as the lava supply region recharges.…”

“…Having fitted 285 spectra and derived spectral radiances at different infrared wavelengths, we examined the relationship between 4.8-μm spectral radiance and total hot-spot thermal emission to see if 4.8-μm spectral radiance can be used as a proxy for total thermal emission. We selected spectral radiance at 4.8 μm because this quantity has been previously shown to be a useful metric of total thermal emission from NIMS data (e.g., Davies et al, 2006); usually provides high signal to noise; corresponds to an atmospheric window for comparison with ground-based telescope observations of Io (e.g., de Pater et al, 2004;Marchis et al, 2005); and is one of the two filters of the Juno JIRAM instrument (Adriani et al, 2014), thus allowing direct comparison of different data sets (Davies, Perry, et al, 2023). Figure 6 shows that this relationship is valid and allows a first-order estimate of total hot-spot thermal emission from a measurement of 4.8-μm spectral radiance.…”

New Global Map of Io’s Volcanic Thermal Emission and Discovery of Hemispherical Dichotomies

“…These wavelengths are particularly sensitive to As a suitable heat flow model discriminator, 60°latitude is used to demarcate Io's polar regions. This latitude was chosen because this was where the greatest changes in heat flow occurred when comparing models, and previous works used this latitude (Milazzo et al 2005;Davies et al 2024) to demark the polar boundary, allowing direct comparison of results.…”

“…The data returned from NASA's Juno spacecraft from its polar orbit around Jupiter have revealed Io's polar volcanoes in the infrared at spatial scales (up to orbit PJ49) as high as 13 km pixel −1 . New Juno Jupiter Infrared Auroral Mapper (JIRAM) hot spot detections (Adriani et al 2014;Mura et al 2020;Davies et al 2024) have been added to previous analyses to create an updated Io volcanic thermal emission map (Figures 1 and 2). JIRAM observations obtained from 2017 March 27 (Juno orbit PJ05) through 2023 March 1 (Juno orbit PJ49) have allowed the identification of 273 active volcanic thermal sources (Davies et al 2024) and the quantification of volcanic thermal emission from Io's major polar volcanoes.…”

“…New Juno Jupiter Infrared Auroral Mapper (JIRAM) hot spot detections (Adriani et al 2014;Mura et al 2020;Davies et al 2024) have been added to previous analyses to create an updated Io volcanic thermal emission map (Figures 1 and 2). JIRAM observations obtained from 2017 March 27 (Juno orbit PJ05) through 2023 March 1 (Juno orbit PJ49) have allowed the identification of 273 active volcanic thermal sources (Davies et al 2024) and the quantification of volcanic thermal emission from Io's major polar volcanoes. The JIRAM data provide a global snapshot of where effusive high-temperature (silicate) volcanic activity is currently taking place on Io.…”