Solar wind interaction with the lunar surface: Observation of energetic neutral atoms on the lunar surface by the Advanced Small Analyzer for Neutrals (ASAN) instrument on the Yutu-2 rover of Chang'E-4.

2020 ◽  
Author(s):  
Martin Wieser ◽  
Stas Barabash ◽  
Xiao-Dong Wang ◽  
Aibing Zhang ◽  
Chi Wang ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Solar Wind ◽  
Lunar Surface ◽  
Lunar Regolith ◽  
Remote Sensing Data ◽  
High Porosity ◽  
Neutral Atoms ◽  
Solar Wind Interaction ◽  
Energetic Neutral Atoms ◽  
Nominal Performance

<p>A fraction of up to 20% of the solar wind impinging onto the lunar surface is reflected as energetic neutral atoms back to space, as established by remote sensing, e.g. by the SARA instrument on Chandrayaan-1 or by IBEX. Mapping of these reflected energetic neutral atoms to the surface opened a new way to remotely study the solar wind precipitation onto the surface. However, the high reflection rate remained an enigma given the high porosity of the lunar regolith, but no measurements directly on the surface were available.</p><p>With the Advanced Small Analyzer for Neutrals (ASAN) mounted on the Yuyu-2 the rover of Chang'E-4, for the first time measurements of the energetic neutral atom flux originating from the lunar surface were preformed directly on the lunar surface itself. ASAN measures with a single angular pixel the energy spectrum of energetic neutral atoms reflected or sputtered form the surface with coarse mass resolution. ASAN uses the mobility of the rover to cover different solar wind illumination angles and scattering angles from the surface.</p><p>Since the landing of Chang'E-4 in the Von Kármán crater on the lunar far side in January 2019, ASAN has spent more than one year on the lunar surface and performed typically two measurement sessions per lunar day with nominal performance.</p><p>We review the ASAN instrument status and operations; present energy and mass spectra of energetic neutral atoms backscattered and sputtered from the surface, and discuss sputtering yields observed during different observation sessions. We put these observations into context of earlier remote sensing data by the SARA instrument on Chandrayaan-1.</p>

scholarly journals Investigating the Retention of Solar Wind Implanted Helium-3 on the Moon from the Analysis of Multi-Wavelength Remote Sensing Data

2020 ◽  
Vol 12 (20) ◽  
pp. 3350
Author(s):  
Shashwat Shukla ◽  
Valentyn Tolpekin ◽  
Shashi Kumar ◽  
Alfred Stein
Keyword(s):  
Remote Sensing ◽  
Solar Wind ◽  
Remote Sensing Data ◽  
Physical Nature ◽  
The Moon ◽  
Near Surface ◽  
Energy Demands ◽  
Multi Wavelength ◽  
High Dielectric ◽  
Weathering Effects

The Moon has a large potential for space exploration and mining valuable resources. In particular, 3He provides rich sources of non-radioactive fusion fuel to fulfill cislunar and Earth’s energy demands, if found economically feasible. The present study focuses on developing advanced techniques to prospect 3He resources on the Moon from multi-sensor remote sensing perspectives. It characterizes optical changes in regolith materials due to space weathering as a new retention parameter and introduces a novel machine learning inversion model for retrieving the physical properties of the regolith. Our analysis suggests that the reddening of the soil predominantly governs the retention, along with attenuated mafic band depths. Moreover, semi-variograms show that the spatial variability of 3He is aligned with the episodic weathering events at different timescales. We also observed that pyroclastic regoliths with high dielectric constant and increased surface scattering mechanisms exhibited a 3He abundant region. For ejecta cover, the retention was weakly associated with the dielectric contrast and a circular polarization ratio (CPR), mainly because of the 3He-deficient nature of the regolith. Furthermore, cross-variograms revealed inherent cyclicity attributed to the sequential process of weathering effects. Our study provides new insights into the physical nature and near-surface alterations of lunar regoliths that influence the spatial distribution and retention of solar wind implanted 3He.

scholarly journals Emission of energetic neutral atoms measured on the lunar surface by Chang’E-4

2020 ◽  
Vol 189 ◽  
pp. 104970 ◽  
Author(s):  
Aibing Zhang ◽  
Martin Wieser ◽  
Chi Wang ◽  
Stas Barabash ◽  
Wenjing Wang ◽  
...  
Keyword(s):  
Lunar Surface ◽  
Neutral Atoms ◽  
Energetic Neutral Atoms

The lunar regolith: physical characteristics and dynamics

1977 ◽  
Vol 285 (1327) ◽  
pp. 273-278 ◽  
Keyword(s):  
Grain Size ◽  
Solar Wind ◽  
Lunar Surface ◽  
Lunar Regolith ◽  
Size Fraction ◽  
Size Frequency Distribution ◽  
Sample Mean ◽  
Size Frequency ◽  
Constructive Process ◽  
Mean Grain Size

The fine size fraction of the lunar regolith (less than 1 mm mean particle diameter) is composed mostly of particles that owe their origins either directly or indirectly to the impacts of meteoroids on the lunar surface. Comminution of pre-existing rocks and particles is the dominant process affecting the characteristics of the regolith. However, agglutination of pre-existing particles by the glassy, molten spatter and ejecta from small meteoroid impacts is a competing constructive process of low efficiency. Grain size frequency distributions of the less than 1 mm fraction of the regolith tend to be slightly bimodal, with a broad mode in the 1-40 size range (500- 62.5 pm due mostly to agglutination and another mode at approximately 50 (31.3 pm) and finer that appears to be caused by the ballistic influx of fine particles from older (finer) regolith. In general, the size frequency distribution curves are nearly symmetrical and indicate poor to very poor sorting. There is a strong correlation of sample mean grain size (and other size parameters) with the length of time that the regolith has had to accumulate at each landing site. The greater the total length of regolith accumulation time, the greater the comminution by meteoroids, and hence the finer the sample mean grain size and the greater the total agglutinate content. These properties also correlate positively with solar wind implanted carbon and nitrogen contents. Thus, sample mean size, agglutinate content, solar wind nitrogen and carbon, as well as solar particle track densities, can all be used as measures of regolith ‘maturity’. Local sample collection site geology, such as proximity to boulders or recent craters, strongly influences sample modal particle type populations and grain size characteristics. Lunar chondrules of several types have been identified in the regolith and rock samples. Many of these chondrules have textures that are identical with many meteoritic chondrules. The chondrules in lunar surface materials appear to result from lunar impact processes. It may be that chondrules have originated in many meteorites by some of the same processes. If true, this occurrence has important implications for the origin and history of chondritic meteorites.

What epoch and space region at the heliospheric boundaries are probing IBEX and IMAP observations of interstellar neutral gas populations?

2020 ◽  
Author(s):  
Maciej Bzowski ◽  
Marzena Kubiak ◽  
Jacob Heerikhuisen
Keyword(s):  
Magnetic Field ◽  
Remote Sensing ◽  
Solar Wind ◽  
Solar Cycle ◽  
Plasma Flow ◽  
Solar Cycles ◽  
Neutral Atoms ◽  
Neutral Gas ◽  
Direct Sampling

<p>Interaction between the solar wind and the local interstellar environment has been studied using several observation techniques, including in-situ sampling of the plasma, magnetic field,  energetic ions by the Voyager spacecraft; remote-sensing observations of energetic neutral atoms (IBEX, Cassini); and the primary and secondary populations of interstellar neutral gas (IBEX-Lo). Understanding the processes at the heliospheric boundary and of the conditions outside the heliosphere is typically  done by fitting parameters used in models of this interaction to various observables, including the Voyager crossing distances of the termination shock and the heliopause, the size of the IBEX ribbon and its center directions, the sky distribution of the Lyman-alpha helioglow, and the flux of interstellar gas at 1 au from direct-sampling observations. Typically, it is expected that all or most of these observables are successfully reproduced. Even though the interaction of interstellar neutral gas with the solar wind and solar EUV output is sometimes taken into account, the global heliosphere is usually simulated as a stationary structure, with the solar wind flux, density, and magnetic field variation ignored. However, solar wind is a dynamic phenomenon, which results in variations in the plasma flow both inside and outside the heliopause and in variations of the distance to the heliopause. Based on in-situ solar wind observations, dynamic pressure of the solar wind may change by a factor of 2, which may result in a heliopause distance change by 50%, counting from the lowest-pressure conditions.</p><p>Interstellar neutral atoms reaching detectors at 1 au or contributing to the helioglow observed from 1 au need very different times to travel from the interaction  region , typically located at ~1.75 of the heliopause distance to 1 au. While the primary ISN atoms take 3—4 solar cycles to travel from this region to 1 au, with a physical time spread (not an uncertainty!) of about one solar cycle, the atoms from secondary population take as much as 15 solar cycles, with a large spread of 7 solar cycles. This implies that ISN He atoms sampled by IBEX-Lo, as well as those observed as the helioglow, originate from two different and disparate epochs. While it may be expected that the interstellar conditions at a time scale of 200 years are little variable, solar wind is definitely varying, with secular changes superimposed on the solar cycle variation.</p><p>Direct-sampling observations provide information on the plasma flow in the OHS inside ~60° around the inflow direction, with well-defined regions of the OHS contributing atoms to individual pixels observed by IBEX and IMAP at different orbits. However, the information obtained is heavily averaged over time, and the epoch  imprinted on these population is very different to the epochs characteristic for in-situ observations from the Voyagers (by 50 to 170 years!)  and remote-sensing observations of the much faster-running energetic neutral atoms.</p>

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