Structure of the Heliosphere and Heliotail from different MHD models as Probed by ENA maps

Abstract:

The canonical view of the shape of the heliosphere until recently was that it has a long comet-like tail. This view is being challenged and it is now debated whether the heliosphere has a long comet-like shape, has a bubble shape, or has a “croissant”-like shape and these options are being investigated prompted through observations and modeling.

One direct way to probe the structure of the heliotail is through energetic neutral atom (ENA) maps. These ENAs have been observed by the Interstellar Boundary Explorer (IBEX) at energies of 0.5-6 keV by the IBEX-Hi instrument and show a multi-lobe structure. These lobes were interpreted as signatures of slow and fast wind within a long heliospheric tail as part of the 11-year solar cycle (McComas et al. 2013; Zirnstein et al. 2017). In contrast, higher energy ENAs observed by CASSINI suggest that the heliosphere is round (Dialynas et al. 2017).

Opher et al. (2015) suggest that the heliosphere has two lobes (is “croissant”-like). They extend their global 3D MHD model to treat thermal plasma and pickup ions as separate fluids and show that this treatment deflates the heliosphere leading to a smaller and rounder shape (Opher et al. 2020). Izmodenov et al. 2020 argue for confinement but in a long extended tail.

Regardless of the shape of the heliotail, the models agree that the solar magnetic field in the inner heliosheath has a “slinky” structure (Opher et al. 2015; Pogorelov et al. 2015; Izmodenov et al. 2015) that confines the heliosphere plasma.

In this work, as part of the recently funded SHIELD (Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics ) center which is now in Phase I, we revisit two different MHD models (Izmodenov et al. 2018; Opher et al. 2020) and explore how the different physical assumptions manifest in ENA maps. We comment as well on how the conditions ahead of the heliosphere in the VLISM are different in the two models.