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Zirnstein EJ, Möbius E, Zhang M, Bower J, Elliott HA, McComas DJ, Pogorelov NV, Swaczyna P. In Situ Observations of Interstellar Pickup Ions from 1 au to the Outer Heliosphere. SPACE SCIENCE REVIEWS 2022; 218:28. [PMID: 35574273 PMCID: PMC9085710 DOI: 10.1007/s11214-022-00895-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 04/18/2022] [Indexed: 05/08/2023]
Abstract
Interstellar pickup ions are an ubiquitous and thermodynamically important component of the solar wind plasma in the heliosphere. These PUIs are born from the ionization of the interstellar neutral gas, consisting of hydrogen, helium, and trace amounts of heavier elements, in the solar wind as the heliosphere moves through the local interstellar medium. As cold interstellar neutral atoms become ionized, they form an energetic ring beam distribution comoving with the solar wind. Subsequent scattering in pitch angle by intrinsic and self-generated turbulence and their advection with the radially expanding solar wind leads to the formation of a filled-shell PUI distribution, whose density and pressure relative to the thermal solar wind ions grows with distance from the Sun. This paper reviews the history of in situ measurements of interstellar PUIs in the heliosphere. Starting with the first detection in the 1980s, interstellar PUIs were identified by their highly nonthermal distribution with a cutoff at twice the solar wind speed. Measurements of the PUI distribution shell cutoff and the He focusing cone, a downwind region of increased density formed by the solar gravity, have helped characterize the properties of the interstellar gas from near-Earth vantage points. The preferential heating of interstellar PUIs compared to the core solar wind has become evident in the existence of suprathermal PUI tails, the nonadiabatic cooling index of the PUI distribution, and PUIs' mediation of interplanetary shocks. Unlike the Voyager and Pioneer spacecraft, New Horizon's Solar Wind Around Pluto (SWAP) instrument is taking the only direct measurements of interstellar PUIs in the outer heliosphere, currently out to ∼ 47 au from the Sun or halfway to the heliospheric termination shock.
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Affiliation(s)
- E. J. Zirnstein
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 USA
| | - E. Möbius
- Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 USA
| | - M. Zhang
- Department of Physics and Space Sciences, Florida Institute of Technology, Melbourne, FL 32901 USA
| | - J. Bower
- Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 USA
| | - H. A. Elliott
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX 78228 USA
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249 USA
| | - D. J. McComas
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 USA
| | - N. V. Pogorelov
- Department of Space Science, The University of Alabama in Huntsville, Huntsville, AL 35805 USA
- Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville, Huntsville, AL 35805 USA
| | - P. Swaczyna
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 USA
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Galli A, Baliukin II, Bzowski M, Izmodenov VV, Kornbleuth M, Kucharek H, Möbius E, Opher M, Reisenfeld D, Schwadron NA, Swaczyna P. The Heliosphere and Local Interstellar Medium from Neutral Atom Observations at Energies Below 10 keV. SPACE SCIENCE REVIEWS 2022; 218:31. [PMID: 35673597 PMCID: PMC9165285 DOI: 10.1007/s11214-022-00901-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Accepted: 05/05/2022] [Indexed: 05/08/2023]
Abstract
As the heliosphere moves through the surrounding interstellar medium, a fraction of the interstellar neutral helium, hydrogen, and heavier species crossing the heliopause make it to the inner heliosphere as neutral atoms with energies ranging from few eV to several hundred eV. In addition, energetic neutral hydrogen atoms originating from solar wind protons and from pick-up ions are created through charge-exchange with interstellar atoms. This review summarizes all observations of heliospheric energetic neutral atoms and interstellar neutrals at energies below 10 keV. Most of these data were acquired with the Interstellar Boundary Explorer launched in 2008. Among many other IBEX breakthroughs, it provided the first ever all-sky maps of energetic neutral atoms from the heliosphere and enabled the science community to measure in-situ interstellar neutral hydrogen, oxygen, and neon for the first time. These observations have revolutionized and keep challenging our understanding of the heliosphere shaped by the combined forces of the local interstellar flow, the local interstellar magnetic field, and the time-dependent solar wind.
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Affiliation(s)
- André Galli
- Physics Institute, University of Bern, Bern, Switzerland
| | - Igor I. Baliukin
- Space Research Institute of Russian Academy of Sciences, Moscow, Russia
- Moscow Center for Fundamental and Applied Mathematics, Lomonosov Moscow State University, Moscow, Russia
| | - Maciej Bzowski
- Space Research Centre, Polish Academy of Sciences, Warsaw, Poland
| | - Vladislav V. Izmodenov
- Space Research Institute of Russian Academy of Sciences, Moscow, Russia
- Moscow Center for Fundamental and Applied Mathematics, Lomonosov Moscow State University, Moscow, Russia
| | | | | | | | | | | | | | - Paweł Swaczyna
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ USA
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Zirnstein EJ, Giacalone J, Kumar R, McComas DJ, Dayeh MA, Heerikhuisen J. Turbulence in the Local Interstellar Medium and the IBEX Ribbon. THE ASTROPHYSICAL JOURNAL 2020; 888:10.3847/1538-4357/ab594d. [PMID: 32020922 PMCID: PMC6999793 DOI: 10.3847/1538-4357/ab594d] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The effects of turbulence in the very local interstellar medium (VLISM) have been proposed by Giacalone & Jokipii (2015) to be important in determining the structure of the Interstellar Boundary Explorer (IBEX) ribbon via particle trapping by magnetic mirroring. We further explore this effect by simulating the motion of charged particles in a turbulent magnetic field superposed on a large-scale mean field, which we consider to be either spatially-uniform or a draped field derived from a 3D MHD simulation. We find that the ribbon is not double-peaked, in contrast to Giacalone & Jokipii (2015). However, the magnetic mirror force still plays an important role in trapping particles. Furthermore, the ribbon's thickness is considerably larger if the large-scale mean field is draped around the heliosphere. Voyager 1 observations in the VLISM show a turbulent field component that is stronger than previously thought, which we test in our simulation. We find that the inclusion of turbulent fluctuations at scales ≳100 au and power consistent with Voyager 1 observations produces a ribbon whose large-scale structure is inconsistent with IBEX observations. However, restricting fluctuations to <100 au produces a smoother ribbon structure similar to IBEX observations. Different turbulence realizations produce different small-scale features (≲10°) in the ribbon, but its large-scale structure is robust if the maximum fluctuation size is ≲50 au. This suggests that the magnetic field structure at scales ≲50 au is determined by the heliosphere-VLISM interaction and cannot entirely be represented by pristine interstellar turbulence.
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Affiliation(s)
- E J Zirnstein
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - J Giacalone
- Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721, USA
| | - R Kumar
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - D J McComas
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - M A Dayeh
- Southwest Research Institute, San Antonio, TX 78228, USA
| | - J Heerikhuisen
- Department of Mathematics and Statistics, University of Waikato, Hamilton, New Zealand
- Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35899, USA
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Zirnstein EJ, Swaczyna P, McComas DJ, Heerikhuisen J. Parallax of the IBEX Ribbon Indicates a Spatially-Retained Source. THE ASTROPHYSICAL JOURNAL 2019; 879:106. [PMID: 31395988 PMCID: PMC6687312 DOI: 10.3847/1538-4357/ab2633] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In 2009, the Interstellar Boundary Explorer (IBEX) discovered the existence of a narrow "ribbon" of intense energetic neutral atom (ENA) emission projecting approximately a circle in the sky. It is believed that the ribbon originates from outside of the heliopause in radial directions ( r ) perpendicular to the local interstellar magnetic field (ISMF), B , i.e., B∙ r = 0. Swaczyna et al. (2016a) estimated the distance to the IBEX ribbon via the parallax method comparing the ribbon position observed from the opposite sides of the Sun. They found a parallax angle of 0.41° ± 0.15°, yielding a distance of140 - 38 + 84 au to a portion of the ribbon at high ecliptic latitudes. In this study, we demonstrate how the apparent shift of the ribbon in the sky, and thus the apparent distance to the ribbon's source found via the parallax, depends on the transport effects of energetic ions outside the heliopause. We find that the apparent shift of the ribbon based on the "spatial retention" model with ion enhancement near B∙ r = 0, as proposed by Schwadron & McComas (2013), agrees with the parallax of the source region. Parallax is also accurate for a homogeneously-distributed emission source. However, if there is weak pitch angle scattering and ions propagate freely along the ISMF, the apparent shift is significantly smaller than the expected parallax because of the highly anisotropic source. In light of the results from Swaczyna et al. (2016a), our results indicate that the IBEX ribbon source is spatially confined.
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Affiliation(s)
- E J Zirnstein
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - P Swaczyna
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - D J McComas
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - J Heerikhuisen
- Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35899, USA
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