The Sun moves with respect to the local interstellar medium (LISM) and modifies its properties
to heliocentric distances as large as 1 pc. The solar wind (SW) is affected by penetration of the
LISM neutral particles, especially H and He atoms. Charge exchange between the LISM atoms and
SW ions creates pickup ions (PUIs) and secondary neutral atoms that can propagate deep into the
LISM. Neutral atoms measured at 1 au can provide us with valuable information on the properties
of pristine LISM. New Horizons provides us with unique measurements of pickup ions in the SW
region where they are thermodynamically dominant. Voyager 1 and 2 spacecraft perform in-situ
measurements of the LISM perturbed by the presence of the heliosphere and relate them to the
unperturbed region. The Interstellar Boundary Explorer (IBEX) makes it possible identify the
3-D structure of the heliospheric interface. We outline the main challenges in the physics of the
SW–LISM interaction. The physical processes that require a focused attention of the heliospheric
community are discussed from the theoretical perspective and space missions necessary for their
investigation. We emphasize the importance of data-driven simulations, which are necessary for
the interpretation and explanation of spacecraft data.
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Turbulence in the Outer Heliosphere
Abstract The solar wind (SW) and local interstellar medium (LISM) are turbulent media. Their interaction is governed by complex physical processes and creates heliospheric regions with significantly different properties in terms of particle populations, bulk flow and turbulence. Our knowledge of the solar wind turbulence nature and dynamics mostly relies on near-Earth and near-Sun observations, and has been increasingly improving in recent years due to the availability of a wealth of space missions, including multi-spacecraft missions. In contrast, the properties of turbulence in the outer heliosphere are still not completely understood. In situ observations by Voyager and New Horizons , and remote neutral atom measurements by IBEX strongly suggest that turbulence is one of the critical processes acting at the heliospheric interface. It is intimately connected to charge exchange processes responsible for the production of suprathermal ions and energetic neutral atoms. This paper reviews the observational evidence of turbulence in the distant SW and in the LISM, advances in modeling efforts, and open challenges.
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- PAR ID:
- 10355942
- Date Published:
- Journal Name:
- Space Science Reviews
- Volume:
- 218
- Issue:
- 6
- ISSN:
- 0038-6308
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The Sun moves with respect to the local interstellar medium (LISM) and modifies its properties to heliocentric distances as large as 1 pc. The solar wind (SW) is affected by penetration of the LISM neutral particles, especially H and He atoms. Charge exchange between the LISM atoms and SW ions creates pickup ions (PUIs) and secondary neutral atoms that can propagate deep into the LISM. Neutral atoms measured at 1 au can provide us with valuable information on the properties of pristine LISM. Voyager 1 and 2 spacecraft perform in situ measurements of the LISM perturbed by the presence of the heliosphere and relate them to the unperturbed region. We discuss observational data and numerical simulations that shed light onto the mutual influence of the SW and LISM. Physical phenomena accompanying the SW–LISM interaction are discussed, including the coupling of the heliospheric and interstellar magnetic field at the heliopause.more » « less
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Abstract We present a new three-dimensional, MHD-plasma/kinetic-neutrals model of the solar wind (SW) interaction with the local interstellar medium (LISM), which self-consistently includes neutral hydrogen and helium atoms. This new model also treats electrons as a separate fluid and includes the effect of Coulomb collisions. While the properties of electrons in the distant SW and in the LISM are mostly unknown due to the lack of in situ observations, a common assumption for any global, single-ion model is to assume that electrons have the temperature of the ion mixture, which includes pickup ions. In the new model, electrons in the SW are colder, which results in a better agreement with New Horizons observations in the supersonic SW. In the LISM, however, ions and electrons are almost in thermal equilibrium. As for the plasma mixture, the major differences between the models are in the inner heliosheath, where the new model predicts a charge-exchange-driven cooling and a decrease of the heliosheath thickness. The filtration of interstellar neutral atoms at the heliospheric interface is discussed. The new model predicts an increase in the H density by ∼2% at 1 au. However, the fraction of pristine H atoms decreases by ∼12%, while the density of atoms born in the outer and inner heliosheath increases by 5% and ∼35%, respectively. While at 1 au the density of He atoms remains unchanged, the contribution from the “warm breeze” increases by ∼3%.
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Turbulence is ubiquitous in space plasmas. It is one of the most important subjects in heliospheric physics, as it plays a fundamental role in the solar wind—local interstellar medium interaction and in controlling energetic particle transport and acceleration processes. Understanding the properties of turbulence in various regions of the heliosphere with vastly different conditions can lead to answers to many unsolved questions opened up by observations of the magnetic field, plasma, pickup ions, energetic particles, radio and UV emissions, and so on. Several space missions have helped us gain preliminary knowledge on turbulence in the outer heliosphere and the very local interstellar medium. Among the past few missions, the Voyagers have paved the way for such investigations. This paper summarizes the open challenges and voices our support for the development of future missions dedicated to the study of turbulence throughout the heliosphere and beyond.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s11214-022-00914-2
