Evaluating the Ionospheric Mass Source for Jupiter's Magnetosphere: An Ionospheric Outflow Model for the Auroral Regions

Abstract

Ionospheric outflow is the flow of plasma initiated by a loss of equilibrium along a magnetic field line, which induces an ambipolar electric field due to the separation of electrons and ions in a gravitational field and other mass‐dependent sources. We have developed an ionospheric outflow model using the transport equations to determine the number of particles that flow into the outer magnetosphere of Jupiter. The model ranges from 1,400 km in altitude above the 1 bar level to 2.5 RJ along the magnetic field line and considers H+ and normalH3+ as the main ion constituents. Previously, only pressure gradients and gravitational forces were considered in modeling polar wind. However, at Jupiter we need to evaluate the effect of field‐aligned currents present in the auroral regions due to the breakdown of corotation in the magnetosphere, along with the centrifugal force exerted on the particles due to the fast planetary rotation rate. The total number flux from both hemispheres is found to be 1.3–1.8 × 1028 s−1 comparable in total number flux to the Io plasma source. The mass flux is lower due to the difference in ion species. This influx of protons from the ionosphere into the inner and middle magnetosphere needs to be included in future assessments of global flux tube dynamics and composition of the magnetosphere system.

Proton Outflow Associated With Jupiter's Auroral Processes

“…While these beams are not likely the source of protons in the inner‐most portions of the magnetosphere, they may be an important contribution toward explaining observations of protons dominating the dawn‐side of the outer magnetosphere (McComas et al., 2017c) and far down the magnetotail (McComas et al., 2007, 2017b). If Jupiter is the primary source of magnetospheric protons in the inner magnetosphere (within ∼20 R J ), they are likely sourced at latitudes equatorward of the main emissions and at lower energies than 100 eV discussed in this work, which would also explain why these estimates are on the lower end of previous ionospheric mass fluxes (Nagy et al., 1986; Martin et al., 2020). The mass outflow found here of 1–5 kg s −1 is consistent with the values of 4.3–8.5 kg s −1 predicted to occur within a nominal 2° main oval (Martin et al., 2020).…”

“…If Jupiter is the primary source of magnetospheric protons in the inner magnetosphere (within ∼20 R J ), they are likely sourced at latitudes equatorward of the main emissions and at lower energies than 100 eV discussed in this work, which would also explain why these estimates are on the lower end of previous ionospheric mass fluxes (Nagy et al, 1986;Martin et al, 2020). The mass outflow found here of 1-5 kg s -1 is consistent with the values of 4.3-8.5 kg s -1 predicted to occur within a nominal 2° main oval (Martin et al, 2020). While Juno has made direct observations of ionospheric H + at latitudes between the main emissions and Io's orbital footprint (Valek et al, 2019) and near the equator (Valek et al, 2020), thus far it has been difficult to constrain the ionospheric outflow rate in situ.…”

The Effect of Field‐Aligned Currents and Centrifugal Forces on Ionospheric Outflow at Saturn

“…Previously, Martin et al. (2020), showed that at Jupiter the CF does not surpass the gravitational force until beyond two planetary radii owing to the the larger planetary mass. At Jupiter, considering the effects of FACs and CF on ionospheric outflow shows a 90% increase in total mass source rate (from 3.9 to 7.7 kg s −1 ), whereas in this study the inclusion of FACs and CF increase the total mass source from 3.2 to 17.7 kg s −1 , a 450% increase.…”

“…Martin et al. (2020) argued for the presence of an additional subauroral source region powered by radial currents in equatorial region of Jupiter's magnetosphere, based on the data found by Valek et al. (2019).…”

“…The following section outlines the multifluid model used in this study, previously developed for the Jupiter system by Martin et al. (2020). This ionospheric outflow model accounts for the CF acting on the plasma due to the quick rotation of Saturn's magnetosphere, plus the presence of FACs in the auroral regions.…”