Mass transport in Jupiter’s magnetosphere – driven by internal or external processes

Overview:

Thanks to mass provided by the solar wind, mass flow in planetary magnetospheres is a ubiquitous phenomenon, even in systems that have negligible internal sources of mass. Our proposed project studies Jupiter, our solar system’s most extreme example of an internally sourced mass-dominated magnetosphere, to test current ideas about how mass flow is regulated: by physical processes deep within the magnetosphere (internal) or at the boundary between open and closed field lines in the middle magnetosphere (external).

In a counter-intuitive manner, rather than being flung out immediately by centrifugal forces, material from Jupiter’s volcanic moon Io is impounded into a dense ring of ions encircling Jupiter in the vicinity of Io’s orbit called the Io plasma torus (IPT). Since nearly all the plasma in Jupiter’s magnetosphere flows through the IPT first, the mechanisms that govern radial diffusion in the IPT govern mass flow in the magnetosphere as a whole. Our research, in which we watch the response of Jupiter’s magnetosphere to the influx of material from a volcanic eruption on Io, will help determine if processes initiated inside the IPT or in Jupiter’s middle magnetosphere are regulating radial diffusion in the IPT.

Our proposed project uses observations recorded by a unique facility, the Io Input/Output observatory (IoIO). IoIO is a small-aperture robotic coronagraph that operates nightly, contemporaneously recording narrow-band images of the IPT in [SII] 673.1 nm and neutral sodium at 589 nm in the vicinity of Io and Jupiter. Our proposed effort supports the application of mature models to describe the emissions observed by IoIO to accurately constrain a mass balance equation of the material flowing into and out of the IPT. IoIO also conducts astrometry on the IPT to measure its the east-west offset. This offset increases when the mechanisms external to the IPT hypothesized to drive mass flow operate. Thus, one, compact, dedicated observatory can answer our science question: if the IPT shift is seen to lead plasma diffusion from the IPT, mass flow in Jupiter’s magnetosphere is externally driven, if it lags or is not correlated, mass flow is internally driven.

Intellectual Merit:

Significant progress has been made in the past decade understanding the mechanisms that govern radial diffusion in the IPT, and thus mass transport in Jupiter’s magnetosphere as a whole. It has been found that, though small in mass and number density relative to the IPT, a population of superthermal electrons plays a key role. However, the source of these electrons has not been conclusively determined. Theoretical considerations suggests they are generated within the IPT. Observational studies that concentrate on UV emissions excited by the hot electrons come to inconclusive results about whether they are generated internally or externally. Our observational methodology relies on emission excited by the majority population of electrons (thermal) and thus probes mass transport in the densest part of the IPT. By determining whether or not internal or external processes trigger radial diffusion in the IPT without reliance on observation of the hot electrons, we can provide important independent validation of their role and origin.

Broader Impact:

Pew Research polls indicate that educational and workplace discrimination are one of the primary barriers that discourage minorities in the STEM fields. Our proposed effort addresses this issue by creating a children’s book, The Misfit Telescope and companion website and social media stream that use the benefits of diversity in scientific instrumentation as a parable to illustrate the benefits of racial and cultural inclusivity. Through the adventures of its main characters IoIO, Keck and Hubble, the book shows both the value of both being in the minority and having a different point of view and being in the majority and accepting and respecting the minority point of view. The Misfit Telescope will be produced by PSI’s award winning public outreach team, which has created resources such as the Workshops in Science Education and Resources (WISER) teacher training program and CosmoQuest, a popular citizen science outreach website.