Global mapping of lunar crustal magnetic fields by Lunar Prospector

Mitchell, D. L.; Halekas, J. S.; Lin, R. P.; Frey, S.; Hood, L. L.; Acuña, M. H.; Binder, A. B.

doi:10.1016/j.icarus.2007.10.027

Cited by 176 publications

(190 citation statements)

References 29 publications

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“…The Apollo missions shortly after, however, did detect small areas of weak crustal magnetic fields (Dyal et al 1970(Dyal et al , 1974Sharp et al 1973;Fuller 1974;Russell et al 1974). Recent high-resolution measurements characterized these LMAs to have size up to several hundred kilometers with surface magnetic field strengths ranging from 0.1 up to 1000 nT (Lin et al 1998;Mitchell et al 2008;Purucker 2008;Richmond & Hood 2008;Purucker & Nicholas 2010). Since LMAs are rather tiny compared to typical ion plasma scales in the solar wind, the solar wind-LMA interaction is dominated by highly nonadiabatic physical processes(e.g., Deca et al 2014Deca et al , 2015Howes et al 2015, and reference therein).…”

Section: Lunar Magnetic Anomalymentioning

confidence: 99%

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Olshevsky

Deca

Divin

et al. 2016

ApJ

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We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind,and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3-9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their crosssections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data.

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Section: Lunar Magnetic Anomalymentioning

confidence: 99%

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Olshevsky

Deca

Divin

et al. 2016

ApJ

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“…We show a map of all 4902 data points in Fig. 5, with surface crustal field strength contours from an LP ER map constructed using data from the quiet lunar plasma wake and terrestrial magnetotail lobe regions (Mitchell et al, 2008). Recent simulations show that this map primarily represents crustal magnetization with spatial wavelengths greater than ten km (Halekas et al, 2010a).…”

Section: Distribution Of Eventsmentioning

confidence: 99%

Solar wind electron interaction with the dayside lunar surface and crustal magnetic fields: Evidence for precursor effects

et al. 2012

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Electron distributions measured by Lunar Prospector above the dayside lunar surface in the solar wind often have an energy dependent loss cone, inconsistent with adiabatic magnetic reflection. Energy dependent reflection suggests the presence of downward parallel electric fields below the spacecraft, possibly indicating the presence of a standing electrostatic structure. Many electron distributions contain apparent low energy (<100 eV) upwardgoing conics (58% of the time) and beams (12% of the time), primarily in regions with non-zero crustal magnetic fields, implying the presence of parallel electric fields and/or wave-particle interactions below the spacecraft. Some, but not all, of the observed energy dependence comes from the energy gained during reflection from a moving obstacle; correctly characterizing electron reflection requires the use of the proper reference frame. Nonadiabatic reflection may also play a role, but cannot fully explain observations. In cases with upward-going beams, we observe partial isotropization of incoming solar wind electrons, possibly indicating streaming and/or whistler instabilities. The Moon may therefore influence solar wind plasma well upstream from its surface. Magnetic anomaly interactions and/or non-monotonic near surface potentials provide the most likely candidates to produce the observed precursor effects, which may help ensure quasi-neutrality upstream from the Moon.

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“…Ref. 40), which for example can be important for obstacles in the solar wind. Such effects could lead to modifications of the electron distribution by altering the absorption efficiency and introducing electrons at different energies, but regardless of the details, the net charge of electrons and of ions removed from a dense flowing plasma should be approximately equal everywhere on the insulator surface.…”

Section: Discussionmentioning

confidence: 99%

“…That is a very different regime than the one studied here, and can lead to enhancement of the perpendicular kinetic energy of electrons rather than the parallel one. In that limit reflection off crustal magnetic fields near the lunar surface 40 provide an alternative electron-reflection mechanism to negative charging, and such reflection produces a losscone in the electron distribution, appearing as a conic in the solar-wind frame 41,42 . Similar energy-dependent features would likely arise from reflection by electrostatic structures, leading to much more complicated distribution modifications than the clean drift-energization considered here.…”

Section: Discussionmentioning

confidence: 99%

The electron forewake: Shadowing and drift-energization as flowing magnetized plasma encounters an obstacle

Haakonsen

Hutchinson

2015

Physics of Plasmas

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Flow of magnetized plasma past an obstacle creates a traditional wake, but also a forewake region arising from shadowing of electrons. The electron forewakes resulting from supersonic flows past insulating and floating-potential obstacles are explored with 2D electrostatic particle-in-cell simulations, using a physical ion to electron mass ratio. Drift-energization is discovered to give rise to modifications to the electron velocitydistribution, including a slope-reversal, providing a novel drive of forewake instability. The slope-reversal is present at certain locations in all the simulations, and appears to be quite robustly generated. Wings of enhanced electron density are observed in some of the simulations, also associated with drift-energization. In the simulations with a floating-potential obstacle, the specific potential structure behind that obstacle allows fast electrons to cross the wake, giving rise to a more traditional shadowing-driven two-stream instability.Fluctuations associated with such instability are observed in the simulations, but this instability-mechanism is expected to be more sensitive to the plasma parameters than that associated with the slope-reversal.

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Global mapping of lunar crustal magnetic fields by Lunar Prospector

Cited by 176 publications

References 29 publications

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Magnetic Null Points in Kinetic Simulations of Space Plasmas

Solar wind electron interaction with the dayside lunar surface and crustal magnetic fields: Evidence for precursor effects

The electron forewake: Shadowing and drift-energization as flowing magnetized plasma encounters an obstacle

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