Strong influence of lunar crustal fields on the solar wind flow

Lue, Charles; Futaana, Yoshifumi; Barabash, S.; Wieser, Martin; Holmström, Mats; Bhardwaj, Anil; Dhanya, M. B.; Würz, Peter

doi:10.1029/2010gl046215

Cited by 134 publications

(173 citation statements)

References 22 publications

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“…" Hada et al [2003] performed simulations showing that for typical Mach numbers, on the order of~20% reflected protons tip the shock into a nonstationary regime. At the Moon, we regularly observe 20% or more reflected protons at low altitudes (Lue et al [2011] report up to 50%). Thus, it seems plausible that if 20% reflected protons cause the formation of a new shock at an already existing shock, a similar percentage of reflected protons from the Moon could produce a new shock entirely.…”

Section: Discussionmentioning

confidence: 90%

“…New observations show significant (up to 50% or more) reflection of solar wind protons above crustal magnetic fields [Futaana et al, 2003;Saito et al, 2010;Lue et al, 2011]. Given the sub-gyroradius and sub-inertial-length scale of the lunar fields, one would not expect to see such efficient reflection if protons experienced only magnetic forces.…”

Section: Introduction and Contextmentioning

confidence: 99%

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Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Halekas

Poppe

McFadden

et al. 2014

Geophysical Research Letters

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ARTEMIS observes structures near the Moon that display many properties commonly associated with collisionless shocks, including a discontinuity with downstream compression of magnetic field and density, heating and wave activity, and velocity deflections away from the Moon. The two-probe ARTEMIS measurements show that these features do not exist in the pristine solar wind and thus must result from lunar influences. Discontinuity analyses indicate mass flux and heating across the boundary, with the normal velocity dropping from supermagnetosonic to submagnetosonic across the discontinuity. The shock location with respect to crustal magnetic fields suggests a causal relationship, implying that solar wind protons reflected from crustal fields may produce the observed structures. These observations may indicate some of the smallest shocks in the solar system (in terms of plasma scales), driven by solar wind interaction with magnetic fields on the order of the ion gyroradius and inertial length.

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Section: Discussionmentioning

confidence: 90%

Section: Introduction and Contextmentioning

confidence: 99%

Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Halekas

Poppe

McFadden

et al. 2014

Geophysical Research Letters

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“…There are many physical processes that make the real interaction more complex than that. Two examples are magnetic anomalies that deflect the solar wind and will cause downstream disturbances (Lue et al, 2011), and the reflection of solar wind protons by the dayside lunar surface .…”

Section: Discussionmentioning

confidence: 99%

“…An advantage of the discretization is that the divergence of the magnetic field is zero, down to round off errors. Also, the discretization conserves energy very well (Holmström, 2011). The ion macroparticles (each representing a large number of real particles) are deposited on the grid by a cloud-in-cell method (linear weighting), and interpolation of the fields to the particle positions are done by the corresponding linear interpolation.…”

Section: Modelmentioning

confidence: 99%

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The interaction between the Moon and the solar wind

et al. 2012

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We study the interaction between the Moon and the solar wind using a three-dimensional hybrid plasma solver. The proton fluxes and electromagnetical fields are presented for typical solar wind conditions with different magnetic field directions. We find two different wake structures for an interplanetary magnetic field that is perpendicular to the solar wind flow, and for one that is parallell to the flow. The wake for intermediate magnetic field directions will be a mix of these two extreme conditions. Several features are consistent with a fluid interaction, e.g., the presence of a rarefaction cone, and an increased magnetic field in the wake. There are however several kinetic features of the interaction. We find kinks in the magnetic field at the wake boundary. There are also density and magnetic field variations in the far wake, maybe from an ion beam instability related to the wake refill. The results are compared to observations by the WIND spacecraft during a wake crossing. The model magnetic field and ion velocities are in agreement with the measurements. The density and the electron temperature in the central wake are not as well captured by the model, probably from the lack of electron physics in the hybrid model.

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First direct observation of sputtered lunar oxygen

et al. 2014

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Key Points:• We report on the first direct observation of sputtered lunar oxygen • We infer an O surface density of 1.3E7 m −3 and a column density of 1.6E13 m −2 • In addition, we provide the first measurements of backscattered solar wind He Abstract We present the first direct measurement of neutral oxygen in the lunar exosphere, detected by the Chandrayaan-1 Energetic Neutral Analyzer (CENA). With the lunar surface consisting of about 60% of oxygen in number, the neutral oxygen detected in CENA's energy range (11 eV−3.3 keV) is attributed to have originated from the lunar surface, where it was released through solar wind ion sputtering. Fitting of CENA's mass spectra with calibration spectra from ground and in-flight data resulted in the detection of a robust oxygen signal, with a flux of 0.2 to 0.4 times the flux of backscattered hydrogen, depending on the solar wind helium content and particle velocity. For the two solar wind types observed, we derive subsolar surface oxygen atom densities of N 0 = (1.1 ± 0.3) ⋅ 10 7 m −3 and (1.4 ± 0.4) ⋅ 10 7 m −3 , respectively, which agree well with earlier model predictions and measured upper limits. From these surface densities, we derive column densities of N C = (1.5 ± 0.5) ⋅ 10 13 m −2 and (1.6 ± 0.5) ⋅ 10 13 m −2 . In addition, we identified for the first time a helium component. This helium is attributed to backscattering of solar wind helium (alpha particles) from the lunar surface as neutral energetic helium atoms, which has also been observed for the first time. This identification is supported by the characteristic energy of the measured helium atoms, which is roughly 4 times the energy of reflected solar wind hydrogen, and the correlation with solar wind helium content.

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Strong influence of lunar crustal fields on the solar wind flow

Cited by 134 publications

References 22 publications

Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

The interaction between the Moon and the solar wind

First direct observation of sputtered lunar oxygen

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