Investigating the Moon's Interaction With the Terrestrial Magnetotail Lobe Plasma

Abstract

We present observations of the Moon's plasma interaction in Earth's magnetotail lobes by the ARTEMIS mission, and compare these to hybrid model results to constrain the global properties of the lunar electromagnetic environment. We identify, for the first time in the magnetotail lobes, a low‐energy wake extending multiple lunar radii downstream of the Moon along the ambient flow direction. This wake is tilted out of the lunar optical shadow, allowing for detection of the otherwise unobservable cold ambient magnetospheric plasma. Similar eclipse encounters may provide additional opportunities to measure this low‐energy plasma potentially originating from the terrestrial ionosphere. We find lunar ionospheric outflow extending multiple Moon radii downstream that generates asymmetries in the Moon's plasma environment and shares characteristics with the plasma interactions of Rhea, Tethys, and Dione. The extensive ARTEMIS data set may therefore provide additional insights into the plasma environments near moons of the outer solar system.

ARTEMIS Observations of Lunar Nightside Surface Potentials in the Magnetotail Lobes: Evidence for Micrometeoroid Impact Charging

“…Between the dusk terminator (  90 ) and midnight (  180 ), the distribution and median values lie only slightly below unity (median ratio  0.8), indicating that the surface charging theory describes the data generally well. The slight mismatch between the model and data here is likely due to a bias in either the secondary electron emission yield,  M , or the properties of the magnetotail lobe ion population, both of which are difficult to precisely constrain (e.g., Cao et al, 2020;Halekas et al, 2009a;Liuzzo et al, 2021). In contrast, between midnight and the dawn terminator (  270 ), the ratio of the observed-to-theoretical surface potentials falls well below unity, indicating that the lunar surface potential is smaller in magnitude (i.e., less negative) than theory predicts.…”

Triton’s Variable Interaction With Neptune’s Magnetospheric Plasma

“…The hybrid approach is well-documented and has been used to investigate the plasma interactions of many solar system objects. Examples include Earth's Moon (e.g., Holmström et al, 2012;Liuzzo et al, 2021), the moons of Jupiter (e.g., Fatemi et al, 2016;Lipatov & Combi, 2006;Lipatov et al, 2010Lipatov et al, , 2013Liuzzo et al, 2015Liuzzo et al, , 20162019a, 2019bLindkvist et al, 2015;Poppe et al, 2018;Sittler et al, 2013) and Saturn (e.g., Kriegel et al, 2009Kriegel et al, , 2011Kriegel et al, , 2014Ledvina et al, 2012;Lipatov et al, 2012;Sillanpää et al, 2006;Sillanpää & Johnson, 2015), as well as Mercury (e.g., Exner et al, 2018;Kallio & Janhunen, 2003), Venus (e.g., Kallio et al, 2006;Martinecz et al, 2009), Mars (e.g., Kallio & Janhunen, 2001;Modolo et al, 2016), and Pluto (e.g., Barnes et al, 2019;Delamere, 2009;Feyerabend et al, 2017).…”

“…AIKEF has also been used to describe the plasma environment of Pluto, matching data obtained during the New Horizons flyby (Feyerabend et al, 2017). This model has also been applied to study Earth's Moon (Liuzzo et al, 2021;Vernisse et al, 2013;Wiehle et al, 2011), investigating the lunar interaction for the distinct plasma environments the Moon experiences throughout its orbit, matching data from the ARTEMIS spacecraft. In addition, the three-dimensional electromagnetic field output from this model has been used to constrain LIUZZO ET AL.…”

“…This signature is unlike the plasma absorption signatures observed at any other solar system moon so far. At, for example, Saturn's moons Dione, Tethys, and Rhea (e.g., Khurana et al, 2017;Krupp et al, 2020;Roussos et al, 2008;Simon et al, , 2011, or the terrestrial Moon (e.g., Fatemi et al, 2012;Halekas et al, 2005;Liuzzo et al, 2021;Poppe et al, 2014;Travnicek et al, 2005), cavities in the ambient plasma occur directly downstream with respect to the magnetospheric plasma flow direction. Yet, similar to these other moons, the decreased plasma density within Triton's tilted, tube-like density depletion also results in an enhanced magnetic field magnitude in order to maintain pressure balance (see Figures 6a and 6b).…”

Machine Learning Solar Wind Driving Magnetospheric Convection in Tail Lobes

“…Compared to other regions such as the solar wind or the magnetosheath where the ambient plasma density is much higher than that of the lunar ions (Halekas et al, 2011;, the lunar ion density in the terrestrial magnetotail lobes is comparable to or even larger than that of the ambient lobe plasma, and the background flow is commonly sub-Alfvénic (Halekas et al, 2018;Liuzzo et al, 2021). Therefore, the magnetospheric tail lobes are a unique environment in which to study the dynamics of the lunar ions.…”