Jovian Sodium Nebula and Io Plasma Torus S ⁺ and Brightnesses 2017–2023: Insights Into Volcanic Versus Sublimation Supply

Abstract

We present first results derived from the largest collection of contemporaneously recorded Jovian sodium nebula and Io plasma torus in [S II] 6731 Å images assembled to date. The data were recorded by the Planetary Science Institute's Io Input/Output observatory and provide important context to Io geologic and atmospheric studies as well as the Juno mission and supporting observations. Enhancements in the observed emission are common, typically lasting 1–3 months, such that the average flux of material from Io is determined by the enhancements, not any quiescent state. The enhancements are not seen at periodicities associated with modulation in solar insolation of Io's surface, thus physical process(es) other than insolation‐driven sublimation must ultimately drive the bulk of Io's atmospheric escape. We suggest that geologic activity, likely involving volcanic plumes, drives escape.

Plain Language Summary

The Planetary Science Institute's Io Input/Output observatory (IoIO) is composed almost entirely of off‐the‐shelf parts popular with amateur astronomers. IoIO uses special filters to isolate emission from two gasses found around Jupiter: neutral sodium and ionized sulfur. The sodium is thrown out from Io in a vast cloud called the Jovian sodium nebula. The ionized sulfur collects into the Io plasma torus (IPT), a ring‐shaped structure centered around Jupiter that wobbles around Io's orbital path. These gasses ultimately come from Jupiter's highly volcanic moon, Io. We see the Na nebula and IPT brighten frequently. This demonstrates that the majority of the material leaving Io comes from whatever drives the frequent brightening events, with volcanic plumes likely playing a key role. Our results challenge a widely held belief in the scientific community, that the majority of the material in the Na nebula and IPT comes from Io's tenuous global atmosphere, which is fed by the sublimation of surface frosts and is relatively stable in time. Our data set also provides important context for NASA's Juno mission and supporting observations that focus on Io volcanism, the material's likely source, and Io's magnetosphere, the material's ultimate destination.

Key Points

• A large set of Jovian sodium nebula and Io plasma torus S ⁺ images provides context for Io and Jovian magnetospheric studies

• Enhancements in Na and S ⁺ emission last 1–3 months, ruling out insolation‐driven sublimation as their driver

• Volcanic plumes likely play a key role in atmospheric escape