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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, 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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Swaczyna P, Rahmanifard F, Zirnstein EJ, McComas DJ, Heerikhuisen J. Slowdown and Heating of Interstellar Neutral Helium by Elastic Collisions Beyond the Heliopause. THE ASTROPHYSICAL JOURNAL. LETTERS 2021; 911:L36. [PMID: 35198137 PMCID: PMC8861972 DOI: 10.3847/2041-8213/abf436] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Direct sampling of interstellar neutral (ISN) atoms close to the Sun enables studies of the very local interstellar medium (VLISM) around the heliosphere. The primary population of ISN helium atoms has, until now, been assumed to reflect the pristine VLISM conditions at the heliopause. Consequently, the atoms observed at 1 au by the Interstellar Boundary Explorer (IBEX) were used to determine the VLISM temperature and velocity relative to the Sun, without accounting for elastic collisions with other species outside the heliopause. Here, we evaluate the effect of these collisions on the primary ISN helium population. We follow trajectories of helium atoms and track their collisions with slowed plasma and interstellar hydrogen atoms ahead of the heliopause. Atoms typically collide a few times in the outer heliosheath, and only ~1.5% of the atoms are not scattered at all. We use calculated differential cross sections to randomly choose scattering angles in these collisions. We estimate that the resulting primary ISN helium atoms at the heliopause are slowed down by ~0.45 km s-1 and heated by ~1100 K compared to the pristine VLISM. The resulting velocity distribution is asymmetric and shows an extended tail in the antisunward direction. Accounting for this change in the parameters derived from IBEX observations gives the Sun's relative speed of 25.85 km s-1 and temperature of 6400 K in the pristine VLISM. Finally, this paper serves as a source of the differential cross sections for elastic collisions with helium atoms.
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Affiliation(s)
- P. Swaczyna
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - F. Rahmanifard
- Physics Department, Space Science Center, University of New Hampshire, Durham, NH 03824, USA
| | - E. J. Zirnstein
- 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 Mathematics and Statistics, University of Waikato, Hamilton, New Zealand
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Solar Wind Turbulence from 1 to 45 au. IV. Turbulent Transport and Heating of the Solar Wind Using Voyager Observations. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/1538-4357/abab12] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Zirnstein EJ, McComas DJ, Schwadron NA, Dayeh MA, Heerikhuisen J, Swaczyna P. Strong Scattering of ~keV Pickup Ions in the Local Interstellar Magnetic Field Draped Around Our Heliosphere: Implications for the IBEX Ribbon's Source and IMAP. THE ASTROPHYSICAL JOURNAL 2019; 876:10.3847/1538-4357/ab15d6. [PMID: 31359881 PMCID: PMC6662649 DOI: 10.3847/1538-4357/ab15d6] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The leading hypothesis for the origin of the Interstellar Boundary Explorer (IBEX) "ribbon" of enhanced energetic neutral atoms (ENAs) from the outer heliosphere is the secondary ENA mechanism, whereby neutralized solar wind ions escape the heliosphere and, after several charge-exchange processes, may propagate back toward Earth primarily in directions perpendicular to the local interstellar magnetic field (ISMF). However, the physical processes governing the parent protons outside of the heliopause are still unconstrained. In this study, we compute the "spatial retention" model proposed by Schwadron & McComas (2013) in a 3D simulated heliosphere. In their model, pickup ions outside the heliopause that originate from the neutral solar wind are spatially-retained in a region of space via strong pitch angle scattering before becoming ENAs. We find that the ribbon's intensity and shape can vary greatly depending on the pitch angle scattering rate both inside and outside the spatial retention region, potentially contributing to the globally distributed flux. The draping of the ISMF around the heliopause creates an asymmetry in the average distance to the ribbon's source as well as an asymmetry in the ribbon's shape, i.e., radial cross section of ENA flux through the circular ribbon. The spatial retention model adds an additional asymmetry to the ribbon's shape due to the enhancement of ions in the retention region close to the heliopause. Finally, we demonstrate how the ribbon's structure observed at 1 au is affected by different instrument capabilities, and how the Interstellar Mapping and Acceleration Probe (IMAP) may observe the ribbon.
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Affiliation(s)
- E J Zirnstein
- 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 Space Science, University of Alabama in Huntsville, Huntsville, AL 35899, USA
| | - P Swaczyna
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
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Zirnstein EJ, McComas DJ, Schwadron NA, Dayeh MA, Heerikhuisen J, Swaczyna P. Strong Scattering of ~keV Pickup Ions in the Local Interstellar Magnetic Field Draped Around Our Heliosphere: Implications for the IBEX Ribbon's Source and IMAP. THE ASTROPHYSICAL JOURNAL 2019; 876:247. [PMID: 31359881 DOI: 10.3847/1538-4357/ab5b91] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The leading hypothesis for the origin of the Interstellar Boundary Explorer (IBEX) "ribbon" of enhanced energetic neutral atoms (ENAs) from the outer heliosphere is the secondary ENA mechanism, whereby neutralized solar wind ions escape the heliosphere and, after several charge-exchange processes, may propagate back toward Earth primarily in directions perpendicular to the local interstellar magnetic field (ISMF). However, the physical processes governing the parent protons outside of the heliopause are still unconstrained. In this study, we compute the "spatial retention" model proposed by Schwadron & McComas (2013) in a 3D simulated heliosphere. In their model, pickup ions outside the heliopause that originate from the neutral solar wind are spatially-retained in a region of space via strong pitch angle scattering before becoming ENAs. We find that the ribbon's intensity and shape can vary greatly depending on the pitch angle scattering rate both inside and outside the spatial retention region, potentially contributing to the globally distributed flux. The draping of the ISMF around the heliopause creates an asymmetry in the average distance to the ribbon's source as well as an asymmetry in the ribbon's shape, i.e., radial cross section of ENA flux through the circular ribbon. The spatial retention model adds an additional asymmetry to the ribbon's shape due to the enhancement of ions in the retention region close to the heliopause. Finally, we demonstrate how the ribbon's structure observed at 1 au is affected by different instrument capabilities, and how the Interstellar Mapping and Acceleration Probe (IMAP) may observe the ribbon.
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Affiliation(s)
- E J Zirnstein
- 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 Space Science, University of Alabama in Huntsville, Huntsville, AL 35899, USA
| | - P Swaczyna
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
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Magnetic Waves Excited by Newborn Interstellar Pickup Ions Measured by the Voyager Spacecraft from 1 to 45 au. II. Instability and Turbulence Analyses. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aac839] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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8
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Magnetic Waves Excited by Newborn Interstellar Pickup Ions Measured by the Voyager Spacecraft from 1 to 45 au. I. Wave Properties. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aac83b] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Zirnstein EJ, Heerikhuisen J, Dayeh MA. The Role of Pickup Ion Dynamics Outside of the Heliopause in the Limit of Weak Pitch Angle Scattering: Implications for the Source of the IBEX Ribbon. THE ASTROPHYSICAL JOURNAL 2018; 855:30. [PMID: 29861499 PMCID: PMC5975221 DOI: 10.3847/1538-4357/aaaf6d] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We present a new model of the Interstellar Boundary Explorer (IBEX) ribbon based on the secondary energetic neutral atom (ENA) mechanism, under the assumption that there is negligible pitch angle scattering of pickup ions (PUIs) outside the heliopause. Using the results of an MHD-plasma/kinetic-neutral simulation of the heliosphere, we generate PUIs in the outer heliosheath, solve their transport using guiding center theory, and compute ribbon ENA fluxes at 1 AU. We implement several aspects of the PUI dynamics, including (1) parallel motion along the local interstellar magnetic field (ISMF), (2) advective transport with the interstellar plasma, (3) the mirror force acting on PUIs propagating along the ISMF, and (4) betatron acceleration of PUIs as they are advected within an increasing magnetic field towards the heliopause. We find that ENA fluxes at 1 AU are reduced when PUIs are allowed to move along the ISMF, and ENA fluxes are reduced even more by the inclusion of the mirror force, which pushes particles away from IBEX lines-of-sight. Inclusion of advection and betatron acceleration do not result in any significant change in the ribbon. Interestingly, the mirror force reduces the ENA fluxes from the inner edge of the ribbon more than its outer edge, effectively reducing the ribbon's width by ∼6° and increasing its radius projected on the sky. This is caused by the asymmetric draping of the ISMF around the heliopause, such that ENAs from the ribbon's inner edge originate closer to the heliopause, where the mirror force is strongest.
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Affiliation(s)
- E J Zirnstein
- 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
| | - M A Dayeh
- Southwest Research Institute, San Antonio, TX 78228, USA
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Sokół JM, Kubiak MA, Bzowski M, Swaczyna P. INTERSTELLAR NEUTRAL HELIUM IN THE HELIOSPHERE FROM
IBEX
OBSERVATIONS. II. THE WARSAW TEST PARTICLE MODEL (WTPM). ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0067-0049/220/2/27] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Bzowski M, Swaczyna P, Kubiak MA, Sokół JM, Fuselier SA, Galli A, Heirtzler D, Kucharek H, Leonard TW, McComas DJ, Möbius E, Schwadron NA, Wurz P. INTERSTELLAR NEUTRAL HELIUM IN THE HELIOSPHERE FROM
IBEX
OBSERVATIONS. III. MACH NUMBER OF THE FLOW, VELOCITY VECTOR, AND TEMPERATURE FROM THE FIRST SIX YEARS OF MEASUREMENTS. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0067-0049/220/2/28] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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12
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McComas DJ, Bzowski M, Fuselier SA, Frisch PC, Galli A, Izmodenov VV, Katushkina OA, Kubiak MA, Lee MA, Leonard TW, Möbius E, Park J, Schwadron NA, Sokół JM, Swaczyna P, Wood BE, Wurz P. LOCAL INTERSTELLAR MEDIUM: SIX YEARS OF DIRECT SAMPLING BY
IBEX. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0067-0049/220/2/22] [Citation(s) in RCA: 108] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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