Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium

Galli, André; Würz, Peter; Barabash, S.; Grigoriev, Alexander; Lundin, R.; Futaana, Yoshifumi; Gunell, H.; Holmström, Mats; Roelof, E. C.; Curtis, C. C.; Hsieh, K. C.; Fedorov, A.; Winningham, D.; Frahm, R. A.; Cerulli-Irelli, R.; Bochsler, P.; Krupp, N.; Woch, J.; Fränz, M.

doi:10.1086/503765

Cited by 32 publications

(32 citation statements)

References 15 publications

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“…Some possible mechanisms for the creation of keV energetic neutral atoms (ENAs) in the heliosphere include the charge exchange collision of solar wind alpha particles with thermal neutral atoms from the interstellar gas (McComas et al 2011;Hilchenbach et al 1998;Gruntman 1997). Another important example involves charge exchange collisions between keV solar wind ions and neutral atoms and molecules from planetary and cometary atmospheres (Krasnopolsky & Gladstone 2005), a process which has been seen on Mars and Venus (Galli et al 2006(Galli et al , 2008Futaana et al 2006;Luhmann et al 1992). For magnetized planets, interaction of the magnetospheric ions with planetary or satellite atmospheres can be considered as a regular source of energetic atoms (Lui et al 1996).…”

Section: Introductionmentioning

confidence: 99%

Energy Relaxation of Helium Atoms in Astrophysical Gases

Lewkow

Kharchenko

Zhang

2012

ApJ

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We report accurate parameters describing energy relaxation of He atoms in atomic gases, important for astrophysics and atmospheric science. Collisional energy exchange between helium atoms and atomic constituents of the interstellar gas, heliosphere, and upper planetary atmosphere has been investigated. Energy transfer rates, number of collisions required for thermalization, energy distributions of recoil atoms, and other major parameters of energy relaxation for fast He atoms in thermal H, He, and O gases have been computed in a broad interval of energies from 10 meV to 10 keV. This energy interval is important for astrophysical applications involving the energy deposition of energetic atoms and ions into atmospheres of planets and exoplanets, atmospheric evolution, and analysis of non-equilibrium processes in the interstellar gas and heliosphere. Angular-and energy-dependent cross sections, required for an accurate description of the momentum-energy transfer, are obtained using ab initio interaction potentials and quantum mechanical calculations for scattering processes. Calculation methods used include partial wave analysis for collisional energies below 2 keV and the eikonal approximation at energies higher than 100 eV, keeping a significant energy region of overlap, 0.1-2 keV, between these two methods for their mutual verification. The partial wave method and the eikonal approximation excellently match results obtained with each other as well as experimental data, providing reliable cross sections in the astrophysically important interval of energies from 10 meV to 10 keV. Analytical formulae, interpolating obtained energy-and angular-dependent cross sections, are presented to simplify potential applications of the reported database. Thermalization of fast He atoms in the interstellar gas and energy relaxation of hot He and O atoms in the upper atmosphere of Mars are considered as illustrative examples of potential applications of the new database.

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Section: Introductionmentioning

confidence: 99%

Energy Relaxation of Helium Atoms in Astrophysical Gases

Lewkow

Kharchenko

Zhang

2012

ApJ

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“…These hydrogen ENAs are produced by charge exchange processes between solar wind and pick-up protons and interstellar hydrogen mainly in the inner heliosheath, and therefore their fluxes are sensitive to the physical state of this region. With IBEX the measurements of ENAs from the outer heliosphere will be carried to an unprecedented level: the already existing data recorded by the SOHO (Hilchenbach et al 1998) and the Mars Express spacecraft (Galli et al 2006) were obtained with instruments not designed for that particular task and consequently the interpretation of their findings remains unclear so far.…”

Section: Introductionmentioning

confidence: 99%

Calculation of the energetic neutral atom flux from a 3D time-dependent model heliosphere

Sternal¹,

Fichtner²,

Scherer³

2007

A&A

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With the Interstellar Boundary Explorer (IBEX) the measurement of energetic neutral atoms (ENAs) will enable a remote sensing of the heliospheric boundary region where the solar wind plasma flow meets the interstellar medium. Together with Voyager 1 (& 2) in (and at least near) the healiosheath there will be a very fortunate instrument configuration in space that will allow us to obtain valuable information about the large-scale structure and dynamics of the heliosphere. Following ongoing theoretical discussions we have computed all-sky maps of the differential flux of ENAs produced from charge exchange with solar wind protons in a three-dimensionally structured and time-varying heliosheath. We employ a three-dimensional, time-dependent hydrodynamic model heliosphere to compute the production of ENAs by a generalisation of previous two-dimensional approaches. We find three-dimensionally structured all-sky ENA flux maps that are time-varying due to the solar activity cycle. While the study adds to the complexity of the task to correctly interpret the forthcoming measurements to be made with IBEX, it underlines the potential of this mission to significantly increase our understanding of the structure and dynamics of the heliosphere.

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“…The Voyager spacecraft provide some direct information on the plasma environment in the outer heliosphere, but the state of the neutral gas is unknown, and no observations will be available beyond 130-140 AU, where the power supply onboard the Voyagers will become insufficient. Ulysses has measured neutral interstellar gas directly out to ∼5 AU, and first observations of energetic neutral atoms (ENAs) are confirming their likely production in the (inner) heliosheath between the solar wind termination shock and the heliopause [19,58]. These pioneering measurements will be routinely performed by the Interstellar Boundary Explorer (IBEX, see [36]) which will map the heliosheath between the termination shock and the heliopause by remote imaging of energetic neutral atoms (ENAs).…”

Section: A5: What Are the Properties And Dynamics Of The Interstellarmentioning

confidence: 99%

Interstellar heliospheric probe/heliospheric boundary explorer mission—a mission to the outermost boundaries of the solar system

et al. 2009

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The Sun, driving a supersonic solar wind, cuts out of the local interstellar medium a giant plasma bubble, the heliosphere. ESA, jointly with NASA, has had an important role in the development of our current understanding of the Suns immediate neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of The IHP/HEX Team.Exp Astron (2009) 24:9-46 interstellar matter in the heliosphere. Voyager 1 has recently encountered the innermost boundary of this plasma bubble, the termination shock, and is returning exciting yet puzzling data of this remote region. The next logical step is to leave the heliosphere and to thereby map out in unprecedented detail the structure of the outer heliosphere and its boundaries, the termination shock, the heliosheath, the heliopause, and, after leaving the heliosphere, to discover the true nature of the hydrogen wall, the bow shock, and the local interstellar medium beyond. This will greatly advance our understanding of the heliosphere that is the best-known example for astrospheres as found around other stars. Thus, IHP/HEX will allow us to discover, explore, and understand fundamental astrophysical processes in the largest accessible plasma laboratory, the heliosphere.

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Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium

Cited by 32 publications

References 15 publications

Energy Relaxation of Helium Atoms in Astrophysical Gases

Energy Relaxation of Helium Atoms in Astrophysical Gases

Calculation of the energetic neutral atom flux from a 3D time-dependent model heliosphere

Interstellar heliospheric probe/heliospheric boundary explorer mission—a mission to the outermost boundaries of the solar system

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