Resumo: The heliosphere is an immense shield that protects the solar system from harsh, galactic radiation. This radiation affects not only life on Earth, but human spaceexploration as well. In order to understand the evolution of the heliosphere’s shieldiproperties, we need to understand its structure and large-scale dynamics. The heliosphere is atemplate for all other astrospheres, enabling predictions about the conditions necessary to createhabitable planets. Space science is at a pivotal point in generating new understandings of the heliosphere due to the flood of new in situ data from the Voyager 1 (V1), Voyager 2 (V2), andNew Horizon spacecraft, combined with the energetic neutral atom (ENA) maps generated by IBEX and Cassini.
I this talk I will review some of the most pressing aspects that need understanding in the heliosphere. Among them, the shape of the heliosphere. The canonical view of the structure of the heliosphere is that it has a long comet-like tail. This view is not universally accepted and there is vigorous debate as to whether it possesses a long comet-like structure, is bubble shaped, or is “croissant”-like, a debate that is driven by observations and modeling.
Opher et al. (2015) suggest a heliosphere with two lobes, described as “croissant”-like. An extension of the single ion global 3D MHD model that treats PUIs created in the supersonic solar wind as a fluid separate and distinct from the thermal solar wind plasma yields a heliosphere that is reduced in size and rounder in shape (Opher et al. 2020). In contrast, Izmodenov et al. 2020 argue that a long/extended tail confines the plasma.
One direct way to probe the structure of the tail is through energetic neutral atom (ENA) maps. ENA images of the tail by Interstellar Boundary Explorer (IBEX) at energies of 0.5-6keV exhibit a multi-lobe structure. These lobes are attributed to signatures of slow and fast wind within the extended heliospheric tail as part of the 11-year solar cycle (McComas et al. 2013; Zirnstein et al. 2017). Higher energy ENA observations (>5.2 keV) from the Cassini spacecraft, in conjunction with >28 keV in-situ ions from V1&2/LECP (Dialynas et al. 2017), in contrast, support the interpretation of bubble-like heliosphere.
Regardless of the shape of the heliotail, there is an agreement between models that the solar magnetic field in the inner heliosheath (IHS) possesses a “slinky-like” structure (Opher et al. 2015; Pogorelov et al. 2015; Izmodenov et al. 2015) that helps confine the plasma in the IHS.
I will review some of the recent discoveries and challenges as part of the recently funded NASA Science Center SHIELD (Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics).
Sobre a Palestrante: A Profa. Merav Opher obteve o bacharelado no IFUSP e o doutorado no IAG-USP. Ela realiza pesquisas em plasmas astrofísicos, com interesse especial na estrutura e natureza da heliosfera. Ela foi pós-doutoranda na UCLA, no Jet Propulsion Lab do Caltech, professora associada na George Mason University e, atualmente, é professora titular na Boston University. Recebeu os prêmios PECASE (Presidential Early Career Award for Scientists and Engineers), NSF Young Investigator CAREER award, entre outros. É editora da revista Geophysical Research Letters e integra diversas sociedades científicas.