[P-PS01] Outer Solar System Exploration Today, and Tomorrow

[PPS01-09] Observation of the flow of plasma into and out of Jupiter's magnetosphere during the Juno era

*Jeffrey P Morgenthaler¹、Marissa F Vogt¹、Matthew J Rutala²、Carl Schmidt³、Nicholas M Schneider⁴、Max Marconi¹ (1.PSI、2.DIAS、3.BU、4.LASP)

キーワード：Io, Io plasma torus, Jovian sodium nebula, Jovian magnetosphere, Io volcanism, Exomoons

We report on observations of the Jovian sodium nebula and Io plasma torus being recorded by the Planetary Science Institute's Io Input/Output observatory (IoIO) since 2017. IoIO is a robotic 35 cm coronagraph that records narrow-band images in the sodium 589 nm doublet and S+ 673.1 nm. More than 10,000 images recorded on more than 550 nights are used in this study. These observations provide a unique, near-continuous, record of the escape of sodium- and sulfur-bearing material from Io's atmosphere (see top two panels of Figure). Enhancements in the escape of material from Io's atmosphere provide insights into the physical processes on Io's surface/subsurface that generate the material -- likely volcanism. The IoIO observations of the sodium nebula thus provide a calibration source for models that describe spectroscopic evidence of volcanism on exomoons (e.g., Oza et al., 2019, ApJ 885, 168). For this presentation, we concentrate on the astrometric position of the torus ribbon features, easily measured in the IoIO data, which provide a measurement of the strength of the magnetospheric convection electric field (bottom panel in Figure). This field is related to the tailward extension of the magnetosphere caused by internal (Iogenic plasma) and external (solar wind) pressure. We see evidence of modulation in this electric field on timescales of weeks, which is not easily correlated with indicators of solar wind activity at Jupiter. Neither is the modulation correlated to the surface brightness of the torus, which was implied by previous work (Brown & Bouchez 1997, Science 278, 268). This suggests that, on timescales of weeks, modulations in the convection electric field are primarily governed by two competing processes: (1) the flow of plasma from the torus into the magnetosphere, which will act to strengthen the electric field and (2) loss of plasma from the magnetosphere (e.g., via the release of plasmoids from the magnetotail), which will weaken the electric field. Thus, the IoIO dataset provides an indicator of modulations in the plasma content of the Jovian magnetosphere and is a valuable complement to any mission to Jupiter as well as other remote-sensing observations of the system.