Near Side Research Articles

Reflection imaging of the Moon's interior using deep‐moonquake seismic interferometry

AbstractThe internal structure of the Moon has been investigated over many years using a variety of seismic methods, such as travel time analysis, receiver functions, and tomography. Here we propose to apply body‐wave seismic interferometry to deep moonquakes in order to retrieve zero‐offset reflection responses (and thus images) beneath the Apollo stations on the nearside of the Moon from virtual sources colocated with the stations. This method is called deep‐moonquake seismic interferometry (DMSI). Our results show a laterally coherent acoustic boundary around 50 km depth beneath all four Apollo stations. We interpret this boundary as the lunar seismic Moho. This depth agrees with Japan Aerospace Exploration Agency's (JAXA) SELenological and Engineering Explorer (SELENE) result and previous travel time analysis at the Apollo 12/14 sites. The deeper part of the image we obtain from DMSI shows laterally incoherent structures. Such lateral inhomogeneity we interpret as representing a zone characterized by strong scattering and constant apparent seismic velocity at our resolution scale (0.2–2.0 Hz).

Rb‐Sr resonance ionization geochronology of the Duluth Gabbro: A proof of concept forin situdating on the Moon

RationaleWe report new 87Rb‐87Sr isochron data for the Duluth Gabbro, obtained with a laser ablation resonance ionization mass spectrometer that is a prototype spaceflight instrument. The gabbro has a Rb abundance and a range of Rb/Sr ratios that are similar to those of KREEP‐rich basalts found on the nearside of the Moon. Dating of previously un‐sampled young lunar basalts, which generally have a KREEP‐rich composition, is critical for understanding the bombardment history of the Moon since 3.5 Ga, which in turn informs the chronology of the solar system. Measurements of lunar analogs like the Duluth Gabbro are a proof of concept for in situ dating of rocks on the Moon to constrain lunar history.MethodsUsing the laser ablation resonance ionization mass spectrometer we ablated hundreds of locations on a sample, and at each one measured the relative abundances of the isotopes of Rb and Sr. A delay between the resonant photoionization processes separates the elements in time, eliminating the potential interference between 87Rb and 87Sr. This enables the determination of 87Rb‐87Sr isochron ages without sophisticated sample preparation that would be impractical in a spaceflight context.ResultsWe successfully dated the Duluth Gabbro to 800 ± 300 Ma using traditional isochron methods like those used in our earlier analysis of the Martian meteorite Zagami. However, we were able to improve this to 1100 ± 200 Ma, an accuracy of <1σ, using a novel normalization approach. Both these results agree with the age determined by Faure et al. in 1969, but our novel normalization improves our precision.ConclusionsDemonstrating that this technique can be used for measurements at this level of difficulty makes ~32% of the lunar nearside amenable to in situ dating, which can complement or supplement a sample return program. Given these results and the scientific value of dating young lunar basalts, we have recently proposed a spaceflight mission called the Moon Age and Regolith Explorer (MARE). © 2015 The Authors and Southwest Research Institute. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.

Characterization and Analysis of Near-Earth Objects via Lunar Impact Observations

Asteroid events such as the air blast above Chelyabinsk, Russia, in the spring of 2013 have highlighted the importance of understanding Earth's local asteroid population and the potential threat they pose. While much observational data exists for larger asteroids (those greater than 50 meters in diameter), comparatively little is known of the very small meteoroid population. This study utilized the non-illuminated part of the near side of the Moon as a detection screen upon which the faint flashes of small meteoroids hitting the lunar surface could be detected. Over 80 hours of observations were conducted between the fall of 2010 and the spring of 2013. The observed lunar area was determined nightly and used alongside the impact count to determine a meteoroid flux rate. Impact flashes were calibrated to extinction and color corrected reference stars to estimate the kinetic energies involved. Analysis indicated an average flux rate of 1.09×10−7km−2h−1, corresponding to 1 impactor larger than 3 centimeters in diameter observed every 30 minutes. Further, the size distribution dependence of small impactors was found to be consistent with the power law governing the larger-size meteoroid distribution. This data helps fix the low-end of the asteroid size distribution for solar system evolution models.

Volcanic history of the Imbrium basin: A close-up view from the lunar rover Yutu

We report the surface exploration by the lunar rover Yutu that landed on the young lava flow in the northeastern part of the Mare Imbrium, which is the largest basin on the nearside of the Moon and is filled with several basalt units estimated to date from 3.5 to 2.0 Ga. The onboard lunar penetrating radar conducted a 114-m-long profile, which measured a thickness of ∼5 m of the lunar regolith layer and detected three underlying basalt units at depths of 195, 215, and 345 m. The radar measurements suggest underestimation of the global lunar regolith thickness by other methods and reveal a vast volume of the last volcano eruption. The in situ spectral reflectance and elemental analysis of the lunar soil at the landing site suggest that the young basalt could be derived from an ilmenite-rich mantle reservoir and then assimilated by 10-20% of the last residual melt of the lunar magma ocean.

Study of olivine-rich dark halo crater – Beaumont L in Mare Nectaris using high resolution remote sensing data

Study of dark-haloed craters (DHCs) can provide important information about the geology, mineralogy and evolution of certain hidden mare deposits known as cryptomare. Some DHCs have been identified in the Mare Nectaris region of the near side of the Moon. Beaumont L represents one such DHC situated on the western flank of the Nectaris basin. Moon Mineralogical Mapper (M3) images were used to investigate the composition of DHCs. Morphological investigations have been carried out using Terrain Mapping Camera (TMC) and Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera images. The morphological details captured by TMC and LROC Narrow Angle Camera (NAC) images provide evidence that Beaumont-L is of impact origin and do not show evidence of a volcanic origin. The compositional analysis using M3 data indicates the presence of an olivine rich cryptomare unit excavated due to the Beaumont L impact. Our study also confirms that the band I feature in the reflectance spectra of Beaumont L is completely attributable to olivine deposits without contribution from any type of glass/melt deposits. The presence of olivine in Beaumont L suggests either excavation of olivine-rich cryptomare or a subsurface mafic pluton.

Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data.

The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region.

Subsurface structures of large volcanic complexes on the nearside of the Moon: A view from GRAIL gravity

The lunar nearside large volcanic complexes, such as the Rümker Hills, Aristarchus Plateau, and Marius Hills are likely sites of intense and sustained magmatic activity. These volcanic complexes, recently proposed to be shield volcanoes, are generally located at regionally high elevations and some feature relatively well-localized positive gravity anomalies. Applying localized spectral analyses on high-resolution gravity data obtained from the Gravity Recovery and Interior Laboratory (GRAIL) mission and topography data returned from the Lunar Reconnaissance Orbiter (LRO) spacecraft, we study the subsurface structures of these volcanic complexes. The gravity signal is predicted using a thin elastic lithospheric model that considers both surface and subsurface loads. Best-fit crustal and load densities show that the topographic highs of Rümker Hills, Marius Hills, Gardner and Kepler are mainly composed of material that has a density of more than 2850kgm−3, which is consistent with that of emplaced igneous rocks. Both the Aristarchus Plateau and Hortensius have relatively lower crustal and surface load densities, with mean values around 2550kgm−3, which are well consistent with the average bulk density of the lunar highland crust. These results, together with evidence of multiple volcanic edifices on the surface, suggest that the shallow crusts of the Rümker Hills, Marius Hills, Gardner and Kepler are mainly composed of dense intrusive/extrusive magmatic units, and those of the Aristarchus Plateau and Hortensius are mainly composed of low density materials with only small amounts of superimposed volcanic material. To further constrain the subsurface structures beneath these volcanic complexes, we analyze the Bouguer gravity anomalies for these regions. Results show that dense materials that might be solidified intrusions exist beneath Rümker Hills, Marius Hills, Gardner and Prinz, but no substantial dense materials have been detected beneath the Aristarchus Plateau, Hortensius, Kepler or Cauchy. The different subsurface structures among these large volcanic complexes suggest that the volcanism style at the lunar nearside is different from each other, even for those formed at the same geological time.

Volcanism on farside of the Moon: New evidence from Antoniadi in South Pole Aitken basin

The lunar surface is characterized by asymmetric distribution of its volcanic deposits. The nearside contains about 90% of the mare basalts, while there are a few on the farside with some are in the South Pole Aitken (SPA) basin, which is the largest and oldest impact basin on the Moon. Although the mare volcanism on the nearside of the Moon has been very well characterized, our understanding of the farside is relatively poor. Our geological mapping using Lunar Reconnaissance Orbiter (LRO) and Chandrayaan-1 Moon Mineralogy Mapper (M3) data of 143km Antoniadi impact basin provides new insights into volcanic processes in the southern SPA. Antoniadi has excavated the SPA floor as deep as 9km. Distribution of secondary craters around Antoniadi shows that the basin was formed by oblique impact with the direction of 50° counter-clockwise from 178°E longitude. Our geological mapping has found, for the first time, several volcanic cones (0.2–2.5km diameter) in association with the mare basalt flows. As per morphological classification, these are C, E, N and P type volcanic cones with abundant volcanic fragments in their summit areas. The base and summit diameters of these cones are similar to those of Marius Hills on the nearside of the Moon. The cumulative size frequency distributions of the summit fragments provide a range of power index values between −3 and −9, suggesting the involvement of dynamic fragmentation of the volcanic materials during the eruptive processes. The grabens in the basin floor show evidence for fissure eruption of the mare basalts. The graben near the central peak exposes about 140m thick basalt sequence containing a minimum of five individual lava layers. The crater size–frequency distributions of the mare deposits suggest an age of 1.6Ga for the flows in the central part of the basin, while 2.6Ga for those on the outer floor near the basin wall, indicating the episodic volcanism in the basin. The young volcanism of 1.6Ga is reported for the first time from SPA. The M3 data reveal that the basin materials contain abundant low-Ca pyroxene, while the mare basalts with high-Ca pyroxene. We calculated the liquidus density of mare basalts based on FeO and TiO2 content, which suggest a range of density from 2.7 to 2.8g/cm3, which would be lower than a gross lunar crust. This would imply the emplacement of basaltic lavas through dikes by simple magma buoyancy or over-pressurization of magma chambers, if they present at the crust-mantle boundary when the magma density is greater than the host crust. The 1.6Ga old volcanism in Antoniadi suggests that the mantle beneath the SPA has been conducive for young magmatism, possibly due to presence of KREEP like material in the mantle.

Rupes Recta and the geological history of the Mare Nubium region of the Moon: insights from forward mechanical modelling of the ‘Straight Wall’

Abstract Rupes Recta, also known as the ‘Straight Wall’, is an individual normal fault located in eastern Mare Nubium on the nearside of the Moon. Age and cross-cutting relationships suggest that the maximum age of Rupes Recta is 3.2 Ga, which may make it the youngest large-scale normal fault on the Moon. Based on detailed structural mapping and throw distribution analysis, fault nucleation is interpreted to have occurred near the fault centre, and the fault has propagated bi-directionally, growing northwards and southwards by segment linkage. Forward mechanical modelling of fault topography gives a best-fitting fault dip of approximately 85°, and suggests that Rupes Recta accommodated approximately 400 m of maximum displacement and extends to a depth of around 42 km. The cumulative driving stresses required to form Rupes Recta are similar in magnitude to those that formed normal faults in Tempe Terra, Mars. The spatial and temporal association with Rima Birt, a sinuous rille to the west of Rupes Recta, suggests a genetic relationship between both structures and implies regional extension at the time of formation.

Mineralogy of Mare Serenitatis on the near side of the Moon based on Chandrayaan-1 Moon Mineralogy Mapper (M3) observations

Spectral analysis of Mare Serenitatis has been carried out using Chandrayaan-1 Moon Mineralogy Mapper (M3) data in order to map the compositional diversity of the basaltic units that exist in the basin. Mare Serenitatis is characterized by multiple basaltic flows of different ages indicating a prolonged volcanism subsequent to the basin formation event. Reflectance spectra of fresh craters from the Mare Serenitatis have been analyzed to study the nature and location of the spectral absorption features around 1- and 2-μm respectively, arising due to the electronic charge transition of Fe2+ in the crystal lattice of pyroxenes and/or olivine. Chandrayaan-1 M3 data have been utilized to obtain an Integrated Band Depth (IBD) mosaic of the Serenitatis basin. Based on the spectral variations observed in the IBD mosaic, 13 spectral units have been mapped in the Mare Serenitatis. In the present study, we have also derived spectral band parameters, namely, band center, band strength, band area and band area ratio from the M3 data to study the mineralogical and compositional variations amongst the basaltic units of the studied basin. On the basis of spectral band parameter analysis, the pyroxene compositions of the basaltic units have been determined, which vary from low to intermediate end of the high-Ca pyroxene and probably represent a sub-calcic to calcic augite compositional range. Detailed spectral analyses reveal little variations in the mafic mineralogy of the mare basalts in terms of pyroxene chemistry. The uniformity in pyroxene composition across the basaltic units of Mare Serenitatis, therefore, suggest a probably stable basaltic source region, which might not have experienced large-scale fractionation during the prolonged volcanism that resulted in filling of the large Serenitatis basin.

Spatial heterogeneity in the radiogenic activity of the lunar interior: Inferences from CHACE and LLRI on Chandrayaan-1

In the past, clues on the potential radiogenic activity of the lunar interior have been obtained from the isotopic composition of noble gases like Argon. Excess Argon (40) relative to Argon (36), as compared to the solar wind composition, is generally ascribed to the radiogenic activity of the lunar interior. Almost all the previous estimates were based on, ‘on-the-spot’ measurements from the landing sites. Relative concentration of the isotopes of 40Ar and 36Ar along a meridian by the Chandra’s Altitudinal Composition Explorer (CHACE) experiment, on the Moon Impact Probe (MIP) of India’s first mission to Moon, has independently yielded clues on the possible spatial heterogeneity in the radiogenic activity of the lunar interior in addition to providing indicative ‘antiquity’ of the lunar surface along the ground track over the near side of the moon. These results are shown to broadly corroborate the independent topography measurements by the Lunar Laser Ranging Instrument (LLRI) in the main orbiter Chandrayaan-1. The unique combination of these experiments provided high spatial resolution data while indicating the possible close linkages between the lunar interior and the lunar ambience.

Seismic tomography and geochemical evidence for lunar mantle heterogeneity: Comparing with Earth

We present seismic tomography and geochemical evidence for the existence of significant lateral heterogeneities in the lunar mantle and make a comparison with the Earth's heterogeneity and seismicity. The Procellarum KREEP Terrane (PKT) is a unique province on the nearside of the Moon. It constitutes only about 15% or less of the lunar surface, but appears to owe a large portion of the Moon's radioactive heat-producing elements. We found a correlation between the Thorium (Th) abundance distribution and seismic tomography of the lunar nearside. The area with high Th abundance exhibits a distinct low shear-wave velocity, and the low-velocity anomaly extends down to 300–400km depth below the PKT, suggesting that the thermal and compositional anomaly has a depth extent of 300–400km in the lunar mantle. The distribution of deep moonquakes shows a correlation with the seismic-velocity variations in the deep lunar mantle, similar to the earthquakes which are affected or controlled by structural heterogeneities in the terrestrial crust and upper mantle. The presence of deep moonquakes and seismic-velocity heterogeneities in the mantle implies that the interior of the present Moon may be still thermally active.

Constraints on the flux of meteoritic and cometary water on the Moon from volatile element (N–Ar) analyses of single lunar soil grains, Luna 24 core

We report new nitrogen and argon isotope and abundance results for single breccia clasts and agglutinates from four different sections of the Luna 24 drill core in order to re-evaluate the provenance of N trapped in lunar regolith, and to place limits on the flux of planetary material to the Moon’s surface. Single Luna 24 grains with 40Ar/36Ar ratios <1 show δ15N values between −54.5‰ and +123.3‰ relative to terrestrial atmosphere. Thus, low-antiquity lunar soils record both positive and negative δ15N signatures, and the secular increase of the δ15N value previously postulated by Kerridge (Kerridge, J.F. [1975]. Science 188(4184), 162–164. doi:10.1126/science.188.4184.162) is no longer apparent when the Luna and Apollo data are combined. Instead, the N isotope signatures, corrected for cosmogenic 15N, are consistent with binary mixing between isotopically light solar wind (SW) N and a planetary N component with a δ15N value of +100‰ to +160‰. The lower δ15N values of Luna 24 grains compared to Apollo samples reflect a higher relative proportion of solar N, resulting from the higher SW fluence in the region of Mare Crisium compared to the central near side of the Moon. Carbonaceous chondrite-like micro-impactors match well the required isotope characteristics of the non-solar N component trapped in low-antiquity lunar regolith. In contrast, a possible cometary contribution to the non-solar N flux is constrained to be ⩽3–13%. Based on the mixing ratio of SW to planetary N obtained for recently exposed lunar soils, we estimate the flux of micro-impactors to be (2.2–5.7)×103tonsyr−1 at the surface of the Moon. Our estimate for Luna 24 agrees well with that for young Apollo regolith, indicating that the supply of planetary material does not depend on lunar location. Thus, the continuous influx of water-bearing cosmic dust may have represented an important source of water for the lunar surface over the past ∼1Ga, provided that water removal rates (i.e., by meteorite impacts, photodissociation, and sputtering) do not exceed accumulation rates.

Geological characteristics and model ages of Marius Hills on the Moon

Marius Hills is a volcanic plateau on the nearside of the Moon. It is of great interest for its high concentration of volcanic features, including domes, cones, ridges, and rilles. However, the morphological and chronological characteristics of this plateau were not well studied due to the low resolution of early mission data. This study describes the detailed morphology of the volcanic features using the latest high spatial resolution images of the Terrain Camera (TC) onboard Selene-1 (10 m/pix) and Narrow Angle Camera (NAC) onboard the Lunar Reconnaissance Orbiter (LRO) (0.5 m/pix). We report here some new structures such as skylights and remnants of lava tubes. We have divided spectrally homogenous areas with Clementine UVVIS data and did crater size frequency distribution (CSFD) measurements with Lunar Orbiter (LO) IV and TC images in every spectral unit. We first report absolute model ages of 1.10 Ga for Marius basalt 1, 1.49 Ga for Flamsteed basalt, and 1.46 Ga for Schiaparelli Basalt. In addition, we have identified several younger lava events: they are Marius basalt 2 (814 Ma), medium to low titanium basalt (949 Ma), and undifferentiated medium titanium basalt (687 Ma). Finally, we propose a mantle plume scenario for the formation of Marius Hills, which could solve the inconsistency of previous models.

Erratum to: Assessing consistency of Chang’E-1 and SELENE reference frames using nearly-colocated laser altimetry footprint positions

The consistency of the Chang’E-1 and SELENE reference frames as realized by the footprint positions of laser altimetry measurements of the lunar surface during both missions was analyzed using a global 12-parameter model for small (with respect to unity) deformations and rigid body motions. The rigid body motion and deformation parameters between the two reference frames estimated from nearly-colocated without tie measurements are found to be consistent, i.e., nearly zero for the estimates of the translations, rotations and shear parameters. However, the estimated three strain parameters, which are similar in magnitude and sign, reveal a prominent scale difference, between the Chang’E-1 and SELENE reference frames, of about 0.9 × 10−5. The scale difference can be attributed to calibration of the data sets using the known coordinates of the lunar laser ranging stations all located on the near side of the Moon.

Thorium abundances of basalt ponds in South Pole-Aitken basin: Insights into the composition and evolution of the far side lunar mantle

[1] Imbrian-aged basalt ponds, located on the floor of South Pole-Aitken (SPA) basin, are used to provide constraints on the composition and evolution of the far side lunar mantle. We use forward modeling of the Lunar Prospector Gamma Ray Spectrometer thorium data, to suggest that at least five different and distinct portions of the far side lunar mantle contain little or no thorium as of the Imbrian Period. We also use spatial correlations between local thorium enhancements and nonmare material on top of the basalt ponds to support previous assertions that lower crustal materials exposed in SPA basin have elevated thorium abundances, consistent with noritic to gabbronoritic lithologies. We suggest that the lower crust on the far side of the Moon experienced multiple intrusions of thorium-rich basaltic magmas, prior to the formation of SPA basin. The fact that many of the ponds on the lunar far side have elevated titanium abundances indicates that the far side of the Moon experienced extensive fractional crystallization that likely led to the formation of a KREEP-like component. However, because the Imbrian-aged basalts contain no signs of elevated thorium, we propose that the SPA impact event triggered the transport of a KREEP-like component from the lunar far side and concentrated it on the nearside of the Moon. Because of the correlation between basaltic ponds and basins within SPA, we suggest that Imbrian-aged basaltic volcanism on the far side of the Moon was driven by basin-induced decompressional melting.

Petrogenesis and chronology of lunar meteorite Northwest Africa 4472: A KREEPy regolith breccia from the Moon

Northwest Africa (NWA) 4472 is a polymict lunar regolith meteorite. The sample is KREEP-rich (high concentrations of potassium, rare earth elements and phosphorus) and comprises a heterogeneous array of lithic and mineral fragments. These clasts and mineral fragments were sourced from a range of lunar rock types including the lunar High Magnesian Suite, the High Alkali Suite, KREEP basalts, mare basalts and a variety of impact crater environments. The KREEP-rich nature of NWA 4472 indicates that the sample was ejected from regolith on the nearside of the Moon in the Procellarum KREEP Terrane and we have used Lunar Prospector gamma-ray remote sensing data to show that the meteorite is most similar to (and most likely sourced from) regoliths adjacent to the Imbrium impact basin. U–Pb and Pb–Pb age dates of NWA 4472 phosphate phases reveal that the breccia has sampled Pre-Nectarian (4.35 Ga) rocks related to early episodes of KREEP driven magmatism. Some younger phosphate U–Pb and Pb–Pb age dates are likely indicative of impact resetting events at 3.9–4 Ga, consistent with the suggested timing of basin formation on the Moon. Our study also shows that NWA 4472 has sampled impact melts and glass with an alkali-depleted, incompatible trace element-rich (high Sc, low Rb/Th ratios, low K) compositional signature not related to typical Apollo high-K KREEP, or that sampled by KREEPy lunar meteorite Sayh al Uhaymir (SaU) 169. This provides evidence that there are numerous sources of KREEP-rich protoliths on the Moon.

The phase ratios of the color index: Mapping of two regions of the near side of the Moon

From the ground-based colorimetry performed for two surface regions of the near side of the Moon, images of the phase ratio of the color index C(600 nm/470 nm) have been built for the phase angles between 2° and 95°. It has been found that for phase angles smaller than α ∼ 40°–50°, the color index of the highlands grows with the phase quicker than that of the mare regions. For larger phase angles, α > 50°, a reverse situation is observed. The laboratory data on the spectrophotometry of the lunar samples confirm the peculiarities found in the phase dependence of color. The influence of multiple scattering on the phase dependence of the color of the mare and highland regions of the Moon are discussed.

Simultaneous Observation of Lunar Radar Sounder and Laser Altimeter of Kaguya for Lunar Regolith Layer Thickness Estimate

Simultaneous observations of Lunar Radar Sounder (LRS) and Laser ALTimeter (LALT) of Kaguya, a Japanese lunar exploration project, were carried out for the purpose of mapping regolith layer thickness of the Moon. Nadir surface echo of a high-frequency (5 MHz) pulse of LRS interferes the shallow (<; 10 m) subsurface echo from the bottom of the regolith layer, which subsequently makes the apparent surface be detected at a range deviated from the actual surface range, while the actual surface range is optically detected by LALT. Regolith layer thickness information is retrieved from this range difference after an inversion process. So far, four major maria on the near side of the Moon (Maria Tranquillitatis, Serenitatis, Imbrium, and Oceanus Procellarum) have been investigated, and the mean regolith layer thicknesses of the four maria were found to be about the same, ranging from 6.3 to 6.9 m. However, spatial distribution of areal regolith thickness appears different in eastern maria from western maria, which implies a difference of the growth history of the regolith layer.

Modeling of ionic transport in solid polymer electrolytes

A Monte Carlo model describing the ionic trans port in solid polyme relectrolyte is developed. Single cation simulation is carried out using hopping rate to study the transport mechanism of a thermally activated ion in solid polymer electrolyte. In our model, the ion is able to hop along a polymer chain and to jump between different chains, surmounting energy barriers that consist of polymer's activation energy and the externally applied electric field. The model is able to trace the motion of ion across polymer electrolyte. The mean hopping distance is calculated based on the available open bond in the next nearest side. Random numbers are used to determine the hopping distances, free flight times, final energy and direction of the cation after successful hop. Drift velocity and energy of cation are simulated in our work. The model is expected to be able to simulate the lithium-polymer battery in future.