No 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...

No abstract