Extremely high reflection of solar wind protons as neutral hydrogen atoms from regolith in space

Wieser, Martin; Barabash, S.; Futaana, Yoshifumi; Holmström, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, M. B.; Würz, Peter; Schaufelberger, Audrey; Asamura, Kazushi

doi:10.1016/j.pss.2009.09.012

Cited by 147 publications

(149 citation statements)

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“…The simulations quantifiably confirm the satellite (Halekas et al 2014) findings and the theoretical predictions (Bamford et al 2012), namely that a miniature collisionless shock can be responsible for all the observations (Lin et al 1998;Huixian et al 2005;Wieser et al 2009Wieser et al , 2010Futaana et al 2010;Hashimoto et al 2010;Lue et al 2011;Wang et al 2012;Halekas et al 2014;Yokota et al 2014). Here it is confirmed that the interaction or boundary layer can form well above (i.e., kilometers rather than meters) the lunar surface (depending upon conditions) and need not be a photoelectricsheath (Garrick-Bethell et al 2011) restricted to a few meters above the surface.…”

Section: Introductionsupporting

confidence: 77%

3d Pic Simulations of Collisionless Shocks at Lunar Magnetic Anomalies and Their Role in Forming Lunar Swirls

Bamford

Alves

Cruz

et al. 2016

ApJ

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Investigation of the lunar crustal magnetic anomalies offers a comprehensive long-term data set of observations of small-scale magnetic fields and their interaction with the solar wind. In this paper a review of the observations of lunar mini-magnetospheres is compared quantifiably with theoretical kinetic-scale plasma physics and 3D particlein-cell simulations. The aim of this paper is to provide a complete picture of all the aspects of the phenomena and to show how the observations from all the different and international missions interrelate. The analysis shows that the simulations are consistent with the formation of miniature (smaller than the ion Larmor orbit) collisionless shocks and miniature magnetospheric cavities, which has not been demonstrated previously. The simulations reproduce the finesse and form of the differential proton patterns that are believed to be responsible for the creation of both the "lunar swirls" and "dark lanes." Using a mature plasma physics code like OSIRIS allows us, for the first time, to make a side-by-side comparison between model and space observations. This is shown for all of the key plasma parameters observed to date by spacecraft, including the spectral imaging data of the lunar swirls. The analysis of miniature magnetic structures offers insight into multi-scale mechanisms and kinetic-scale aspects of planetary magnetospheres.

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Section: Introductionsupporting

confidence: 77%

3d Pic Simulations of Collisionless Shocks at Lunar Magnetic Anomalies and Their Role in Forming Lunar Swirls

Bamford

Alves

Cruz

et al. 2016

ApJ

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“…The magnetic field components were observed to rotate in a fashion consistent with the spacecraft passing through a region in which the solar magnetic field was being "draped" around a small magnetic obstacle or "bubble" [1]. Within the narrow barrier region is a low density cavity seen in the ion data [17]. The barrier region is of the order of kilometers across.…”

mentioning

confidence: 73%

“…At 100km Kaguya observed protons reflected back from the magnetic structures with greater energies (by factors 3 to 6) than the incident solar wind flux [13]. Chandrayaan-1 also observed back streaming protons accelerated by similar factors close to the shock surface [11,17]. These higher energy protons are accelerated by the convective electric field seen by the reflected protons in the solar wind flow [13].…”

mentioning

confidence: 99%

Minimagnetospheres above the Lunar Surface and the Formation of Lunar Swirls

et al. 2012

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In this paper we present in-situ satellite data, theory and laboratory validation that show how small scale collisionless shocks and mini-magnetospheres can form on the electron inertial scale length. The resulting retardation and deflection of the solar wind ions could be responsible for the unusual "lunar swirl" patterns seen on the surface of the Moon.Miniature magnetospheres have been found to exist above the lunar surface [1] and are closely related to features known as "lunar swirls" [2]. Mini-magnetospheres exhibit features that are characteristic of normal planetary magnetospheres namely a collisionless shock. Here we show that it is the electric field associated with the small scale collisionless shock that is responsible for deflecting the incoming solar wind around the minimagnetosphere. These ions impacting the lunar surface resulting in changes to the appearance of the albedo of the lunar "soil" [2]. The form of these swirl patterns therefore, must be dictated by the shapes of the collisionless shock.Collisionless shocks are a classic phenomena in plasma physics, ubiquitous in many space and astrophysical scenarios [3]. Well known examples of collisionless shocks exist in the heliosphere, where the shock is formed by the solar wind interacting with a magnetised planet. What is a surprise is the size of the mini-magnetospheres, of the order of several 100 km; orders of magnitude smaller than the planetary versions. Results from various lunar survey missions have built up a good picture of these collisionless shocks.These collisionless shocks have a characteristic structure in which the ions are reflected from a rather narrow layer, of the order of the electron skin depth c/ω pe (where c is the speed of light and ω pe is the electron plasma frequency), by an electrostatic field that is a consequence of the magnetised electrons and unmagnetised ions. The narrow discontinuity in the shock structure produces a specular reflected ion component with a velocity equal to or greater than the incoming solar wind velocity. The reflected ions from a counter-propagating component to the solar wind flow that form the magnetic foot region, which extends about an ion Larmor orbit upstream from the shock. This occurs when the Mach number (the ratio of flow velocity to Alfvén velocity) is of the order 3 or less.We have carried out laboratory experiments using a plasma wind tunnel, to investigate mini-magnetospheres

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“…These ions may be partly neutralized and backscattered from the surface to space (up to 20% for light ions like the SW major components [see McComas et al, 2009;Wieser et al, 2009]), but a significant fraction of the incident ions, increasing with ions atomic mass number, can be implanted on the EB surface while ejecting a surface atom or molecule. Sputtering products from impacts of keV ions can have energies, peaking at few eV with a high-energy non-Maxwellian tail, up to at least several tens eV for a refractory material [Goehlich et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, Chandrayaan-1 Energetic Neutrals Analyzer (CENA) was, in principle, able to measure neutral atoms of 10 eV to 3 keV [Bhardwaj et al, 2005]. This sensor observed an energetic neutral signal from the Moon surface, interpreted as the product of neutralization and backscattering of the solar wind, probably prevailing on sputtering signal at the Moon [Wieser et al, 2009]. The results and sensitivity of CENA could provide an indication for estimating an upper limit of the flux of SHEA around the Moon.…”

Section: Introductionmentioning

confidence: 99%

Observing planets and small bodies in sputtered high-energy atom fluxes

et al. 2011

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[1] The evolution of the surfaces of bodies unprotected by either strong magnetic fields or thick atmospheres in the solar system is caused by various processes, induced by photons, energetic ions, and micrometeoroids. Among these processes, the continuous bombardment of the solar wind or energetic magnetospheric ions onto the bodies may significantly affect their surfaces, with implications for their evolution. Ion precipitation produces neutral atom releases into the exosphere through ion sputtering, with velocity distribution extending well above the particle escape limits. We refer to this component of the surface ejecta as sputtered high-energy atoms (SHEA). The use of ion sputtering emission for studying the interaction of exposed bodies (EB) with ion environments is described here. Remote sensing in SHEA in the vicinity of EB can provide mapping of the bodies exposed to ion sputtering action with temporal and mass resolution. This paper speculates on the possibility of performing remote sensing of exposed bodies using SHEA and suggests the need for quantitative results from laboratory simulations and molecular physic modeling in order to understand SHEA data from planetary missions. In Appendix A, referenced computer simulations using existing sputtering data are reviewed.

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Extremely high reflection of solar wind protons as neutral hydrogen atoms from regolith in space

Cited by 147 publications

References 13 publications

3d Pic Simulations of Collisionless Shocks at Lunar Magnetic Anomalies and Their Role in Forming Lunar Swirls

3d Pic Simulations of Collisionless Shocks at Lunar Magnetic Anomalies and Their Role in Forming Lunar Swirls

Minimagnetospheres above the Lunar Surface and the Formation of Lunar Swirls

Observing planets and small bodies in sputtered high-energy atom fluxes

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