Discovery of Seven Volcanic Outbursts on Io from an Infrared Telescope Facility Observation Campaign, 2016–2022

Abstract

This study analyzes near-infrared measurements of Io, Jupiter's moon, observed over 170 nights from 2016 to early 2022 using the NASA Infrared Telescope Facility (IRTF). During this period, seven new volcanic outbursts—the most energetic volcanic events on Io—were discovered and characterized, increasing the total number of observed outburst events from 18 to 25. We also present simplified criteria for the thermal detection of an outburst, requiring it to be both confined to a specific location of Io and above a threshold intensity in the Lp band (3.8 μm).Our measurements use 2–5 μm photometry in eclipse, Jupiter occultation, and reflected sunlight. In addition to extending the observational data set of Io's dynamic activity, these data provide insights into the temporal and spatial distribution of outbursts on Io. Notably, all seven outbursts were detected in Io's trailing hemisphere. These include Pillan Patera and a newly discovered repeating outburst location at Acala Fluctus. We add these events to the rare category of recurring outbursts; before this, Tvashtar was the only known example. We observed that another outburst at UP 254W decreased in Lp-band intensity by a factor of 2 in 4.5 hr. In 2021 August, Io exhibited high volcanic activity when two powerful outbursts rapidly appeared, propagating east. Our findings underscore IRTF's ongoing contributions to the study of Io.