Chandrayaan-1 observations of backscattered solar wind protons from the lunar regolith: Dependence on the solar wind speed

Lue, Charles; Futaana, Yoshifumi; Barabash, S.; Wieser, Martin; Bhardwaj, Anil; Würz, Peter

doi:10.1002/2013je004582

Cited by 29 publications

(46 citation statements)

References 28 publications

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“…Here we only discussed proton reflections from lunar crustal magnetic fields. Nevertheless, observations indicate that protons also reflect from unmagnetized areas with reflection flux ratio lower than ∼1% [ Saito et al , ; Lue et al , ]. This can be neglected compared to the ∼10% reflection from lunar crustal fields.…”

Section: Discussionmentioning

confidence: 99%

Effects of protons reflected by lunar crustal magnetic fields on the global lunar plasma environment

et al. 2014

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Solar wind plasma interaction with lunar crustal magnetic fields is different than that of magnetized bodies like the Earth. Lunar crustal fields are, for typical solar wind conditions, not strong enough to form a (bow)shock upstream but rather deflect and perturb plasma and fields. Here we study the global effects of protons reflected from lunar crustal magnetic fields on the lunar plasma environment when the Moon is in the unperturbed solar wind. We employ a three‐dimensional hybrid model of plasma and an observed map of reflected protons from lunar magnetic anomalies over the lunar farside. We observe that magnetic fields and plasma upstream over the lunar crustal fields compress to nearly 120% and 160% of the solar wind, respectively. We find that these disturbances convect downstream in the vicinity of the lunar wake, while their relative magnitudes decrease. In addition, solar wind protons are disturbed and heated at compression regions and their velocity distribution changes from Maxwellian to a non‐Maxwellian. Finally, we show that these features persists, independent of the details of the ion reflection by the magnetic fields.

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Section: Discussionmentioning

confidence: 99%

Effects of protons reflected by lunar crustal magnetic fields on the global lunar plasma environment

et al. 2014

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“…If a particle impacts the surface ( x = 0), it is removed from the simulation domain. This is a reasonable approximation because we primarily study plasma interaction with a localized lunar crustal magnetic field, where <1% solar wind ion reflection from the lunar surface [ Saito et al , ; Lue et al , ] can be neglected in comparison with ∼10% average ion reflection from lunar crustal fields [ Lue et al , ]. However, Holmström et al [] showed that the solar wind ion reflection from the lunar surface does not have any noticeable effect on the lunar plasma environment.…”

Section: Modelmentioning

confidence: 99%

Solar wind plasma interaction with Gerasimovich lunar magnetic anomaly

et al. 2015

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We present the results of the first local hybrid simulations (particle ions and fluid electrons) for the solar wind plasma interaction with realistic lunar crustal fields. We use a three‐dimensional hybrid model of plasma and an empirical model of the Gerasimovich magnetic anomaly based on Lunar Prospector observations. We examine the effects of low and high solar wind dynamic pressures on this interaction when the Gerasimovich magnetic anomaly is located at nearly 20∘ solar zenith angle. We find that for low solar wind dynamic pressure, the crustal fields mostly deflect the solar wind plasma, form a plasma void at very close distances to the Moon (below 20 km above the surface), and reflect nearly 5% of the solar wind in charged form. In contrast, during high solar wind dynamic pressure, the crustal fields are more compressed, the solar wind is less deflected, and the lunar surface is less shielded from impinging solar wind flux, but the solar wind ion reflection is more locally intensified (up to 25%) compared to low dynamic pressures. The difference is associated with an electrostatic potential that forms over the Gerasimovich magnetic anomaly as well as the effects of solar wind plasma on the crustal fields during low and high dynamic pressures. Finally, we show that an antimoonward Hall electric field is the dominant electric field for ∼3 km altitude and higher, and an ambipolar electric field has a noticeable contribution to the electric field at close distances (<3 km) to the Moon.

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“…In Figure , we collapse the incidence angle separation of Figure and show the average energy spectra, allowing incidence angles of 0°–75° SZA for five impact speed bins (results for intermediate bins are available in the supporting information). We compare the results with models for the H ENA energy spectrum (F2012; Futaana et al, ) and the previous model for the H + energy spectrum (L2014; Lue et al, ). The L2014 model is a convolution of the H ENA velocity distribution and an exit speed dependence of the positive charge fraction:

f ((), v_{italicexit}) \propto exp ((), \frac{- m_{p} v_{italicexit}^{2}}{2 {italickT}_{italicENA}}) \cdot exp ((), \frac{- v_{c}}{v_{exit}}),

…”

Section: Resultsmentioning

confidence: 99%

“…Scattered proton energy spectra as in Figures and , for a single solar zenith angle bin of 0°–75° and five solar wind speed ( v sw ) bins. Also plotted are the empirical models for neutral hydrogen from Futaana et al (; F2012), for protons from Lue et al (; L2014) and the L2014 model refitted to the ARTEMIS observations.…”

Section: Resultsmentioning

confidence: 99%

“…We refit the model to our observations, by a standard error‐weighted least‐square fitting of the parameters kT ENA and v c . While Lue et al () used a free scaling factor for fitting their results, we here set the model to be consistent with the H ENA scattering efficiency at 20%, such that our model becomes

j_{italicdH +} ((), E_{italicexit}) = j_{dHENA} ((), E_{italicexit}) \cdot exp ((), \frac{- v_{c}}{v_{exit}}) = \frac{0.2 \cdot J_{in}}{2 π} \cdot \frac{E_{italicexit}}{{italickT}_{italicENA}^{2}} \cdot exp ((), \frac{- E_{italicexit}}{{kT}_{ENA}}) \cdot exp ((), \frac{- v_{c}}{v_{exit}}),

where j de is the differential flux (particle number flux within a given directional solid angle and energy span). Note that the division by 2π here approximates the scattering as isotropic.…”

Section: Resultsmentioning

confidence: 99%

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ARTEMIS Observations of Solar Wind Proton Scattering off the Lunar Surface

et al. 2018

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We study the scattering of solar wind protons off the lunar surface, using ion observations collected over 6 years by the ARTEMIS satellites at the Moon. We show the average scattered proton energy spectra, directional scattering distributions, and scattering efficiency, for different solar wind incidence angles and impact speeds. We find that the protons have a scattering distribution that is similar to existing empirical models for scattered hydrogen energetic neutral atoms, with a peak in the backward direction (toward the Sun). We provide a revised model for the scattered proton energy spectrum. We evaluate the positive to neutral charge state ratio by comparing the proton spectrum with existing models for scattered hydrogen. The positive to neutral ratio increases with increasing exit speed from the surface but decreases with increasing impact speed. Combined, these counteracting effects result in a scattering efficiency that decreases from ~0.5% at 300 km/s solar wind speed to ~0.3% at 600 km/s solar wind speed.

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Chandrayaan-1 observations of backscattered solar wind protons from the lunar regolith: Dependence on the solar wind speed

Cited by 29 publications

References 28 publications

Effects of protons reflected by lunar crustal magnetic fields on the global lunar plasma environment

Effects of protons reflected by lunar crustal magnetic fields on the global lunar plasma environment

Solar wind plasma interaction with Gerasimovich lunar magnetic anomaly

ARTEMIS Observations of Solar Wind Proton Scattering off the Lunar Surface

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