Io’s Volcanic Activity from Time Domain Adaptive Optics Observations: 2013–2018

Abstract

We present measurements of the near-infrared brightness of Io's hot spots derived from 2-5 µm imaging with adaptive optics on the Keck and Gemini N telescopes. The data were obtained on 271 nights between August 2013 and the end of 2018, and include nearly 1000 detections of over 75 unique hot spots. The 100 observations obtained between 2013 and 2015 have been previously published in de Kleer and de Pater (2016a); the observations since the start of 2016 are presented here for the first time, and the analysis is updated to include the full five-year dataset. These data provide insight into the global properties of Io's volcanism. Several new hot spots and bright eruptions have been detected, and the preference for bright eruptions to occur on Io's trailing hemisphere noted in the 2013-2015 data (de Kleer and de Pater 2016a) is strengthened by the larger dataset and remains unexplained. The program overlapped in time with Sprint-A/EXCEED and Juno observations of the jovian system, and correlations with transient phenomena seen in other components of the system have the potential to inform our understanding of the impact of Io's volcanism on Jupiter and its neutral/plasma environment. 2 de Kleer et al.Volcanoes are also distributed non-randomly across Io's surface, showing in particular a dearth of activity at the sub-and anti-jovian longitudes, as well as in polar regions (Hamilton et al. 2013;Veeder et al. 2015; de Kleer and de Pater 2016b), although no dataset published to date has had good coverage of the high latitudes. The spatial distribution of Io's surface heat flow may place constraints on models for tidal heat dissipation in Io's interior, or may indicate the degree of fluid flow in Io's mantle through the amount of smoothing in the observed spatial trends relative to the expected patterns. Without allowing for lateral movement of melt, the end-member case of heat deposition in a shallow aesthenosphere predicts higher heat flow at lower latitudes with the greatest heat flow centered at the sub-jovian and anti-jovian regions. In contrast, the end-member case of deep mantle heating results in enhanced heat flow at the poles (Gaskell et al., 1988;Segatz et al., 1988).Determining the temporal and spatial distribution of Io's volcanism requires a large sample size of hot spot detections over a range of timescales. We have been building up a database of thermal emission from individual volcanoes on Io's surface since 2013, when we initiated a time domain campaign of adaptive optics imaging of Io's volcanoes at the Keck and Gemini N telescopes. Io has been observed using adaptive optics on Keck since 2001(Marchis et al. 2002, but only since 2013 has there been a dedicated Io observing program at such high cadence. These observations spatially resolve Io, permitting the identification of individual active volcanoes, and are often made at multiple wavelengths in the 2-5 µm range in order to constrain temperature and total power output. The observations have a typical spatial resolution of ∼100-500 km depending o...

Variability in Io's Volcanism on Timescales of Periodic Orbital Changes

“…A continuation of the high cadence coverage of Loki Patera that has taken place since 2013 due to the addition of sustained monitoring with the Keck and Gemini N telescopes (de Kleer et al, 2019;de Kleer & de Pater, 2016) would have the ability to isolate a single preferred period and distinguish between orbital and geophysical controls on the eruption timescale. A continuation of the high cadence coverage of Loki Patera that has taken place since 2013 due to the addition of sustained monitoring with the Keck and Gemini N telescopes (de Kleer et al, 2019;de Kleer & de Pater, 2016) would have the ability to isolate a single preferred period and distinguish between orbital and geophysical controls on the eruption timescale.…”

“…The timeline of Loki Patera's activity over the time period from 1987 to 2018, as measured from its near‐infrared brightness, is shown in Figure a overplotted on Io's orbital eccentricity, which is smoothed to remove short‐period oscillations and highlight the 480‐day periodicity. The points shown in the plot and used in the analysis are the 3.5–3.8‐μm brightnesses of Loki Patera derived from ground‐based and Galileo NIMS data sets and corrected for geometric foreshortening (Davies et al, ; de Kleer et al, ; de Kleer & de Pater, ; de Pater et al, ; Rathbun & Spencer, , ; Rathbun et al, ). Io's orbital eccentricity is determined for each orbit from the minimum and maximum Io‐Jupiter distance over the course of the orbit, calculated from JPL Horizons data.…”

“…Colors correspond to time and are the same as in (a) to aid in identification of groups of points belonging to single active periods. Data from Rathbun et al (), Rathbun and Spencer (, ), Davies et al (), de Pater et al (), de Kleer and de Pater (), and de Kleer et al ().…”

“…The limitation in distinguishing between scenarios is the large gaps in the coverage to date. A continuation of the high cadence coverage of Loki Patera that has taken place since 2013 due to the addition of sustained monitoring with the Keck and Gemini N telescopes (de Kleer et al, ; de Kleer & de Pater, ) would have the ability to isolate a single preferred period and distinguish between orbital and geophysical controls on the eruption timescale. A projection of the 454‐day cycle predicts the next events to peak near October–November 2019, January 2021, and April 2022, while if events occur at 330–360° phase in the 480‐day eccentricity cycle, the next events will peak around March 2020, July 2021, and November 2022.…”

Formation of Giant Planet Satellites

“…The unprecedented level of detail unveiled by the Voyager flybys (Smith et al 1979a(Smith et al , 1979b as well as the Galileo/Cassini orbiters (Greeley et al 1998;Moore et al 1998;Pappalardo et al 1998;Elachi et al 2005;Stofan et al 2007;Hayes 2016) has incited a veritable revolution in our understanding of these faraway moons, once and for all transforming them from celestial curiosities into bona fide extraterrestrial worlds. This ongoing paradigm shift-sparked during the latter half of the last century -is poised to persist in the coming decades, as Europa Clipper, JUICE, and Dragonfly missions, 19 along with ground-based photometric/spectroscopic observations (Trumbo et al 2017(Trumbo et al , 2019de Kleer et al 2019ade Kleer et al , 2019b, continue to deepen our insight into their geophysical structure. Importantly, all of these developments have added a heightened element of Figure 9, in absence of dissipative effects associated with the presence of the circumplanetary disk, the initial phase of satellite conglomeration proceeds slowly.…”