Lunar Latitude Research Articles

Microphase iron particle growth promoted by solar wind implantation in lunar soils.

Lunar soils record the history and spectral changes resulting from the space-weathering process. The solar wind and micrometeoroids are the main space-weathering agents leading to darkening (decreasing albedo) and reddening (increasing reflectance with longer wavelength) of visible and near-infrared spectra. Nevertheless, their relative contributions are not well constrained and understood. In this study, we examine the near-infrared spectral variation as a function of lunar latitude and chemical composition using remote spectroscopic analysis of mare basalts and swirl regions. The results indicate that the reflectance of lunar mature soils darkens and the spectral slope flattens (reddening effect saturation) in areas of enhanced solar wind flux. We propose a previously unrecognized stage of space weathering (the post-mature stage), in which solar wind implantation may contribute to the growth and coarsening of metallic iron particles into larger microphase iron. This space-weathering mechanism is dominated by the solar wind and has important implications for understanding the alteration processes of airless bodies across our solar system.

Real-time simulation of effective solar irradiance and electric field on the Aristarchus region based on SLDEM2015 data

Taking the Aristarchus region on the Moon as an example, the slope and azimuth of the lunar surface obtained from the high-precision digital elevation model (SLDEM2015) would be used to calculate the effective solar irradiance at noon from 2025 to 2045 when the Aristarchus region is at the perihelion summer/winter solstice and aphelion summer/winter solstice. Second, based on the current balance theory, the equilibrium surface potential and the vertical electric field are calculated. The results show that the topography, lunar latitude, Sun-Moon distance, and seasons have important effects on the distribution characteristics of effective solar irradiance, equilibrium surface potential, and vertical electric field. In addition, it is found that the distance between the Sun and the Moon has a considerable influence on the effective solar irradiation, equilibrium surface potential, and electric field than the seasonal variation. This can provide some support and basis for the time selection of unmanned and manned lunar exploration missions, simulation of landing site environment characteristics, use of solar energy, and early warning and prediction of lunar dust environment.

Lunar-Based Measurements of the Moon’s Physical Libration: Methods and Accuracy Estimates

Computer simulation results are reported for planned lunar-based observations to be conducted using an automated zenith telescope that can be placed at any lunar latitude. Benefits of lunar-based observations are shown, in comparison with lunar laser ranging. It is investigated whether, and how effectively, these observations can be used to determine the lunar rotation parameters (physical libration). The accuracy requirements for these observations are analyzed in view of the accuracy requirements for determining the lunar rotation parameters. The necessary number of telescopes, as well as their optimal locations, is assessed.

Photoelectron distribution on sunlit surface of the Moon: A formalism

An analytical formulation describing the characteristic energy distribution of photoelectrons over the sunlit regolith of the Moon has been presented. In deriving the distribution function, Fowler's approach based on fermionic lattice electrons for photoemission has been coupled with observed solar spectra, photoelectric quantum yield, and latitude dependent surface temperature. It is noticed that the dominant contribution in the photoelectron distribution function comes from extreme ultraviolet photons (3 eV–300 eV) of the solar spectra. The analysis also illustrates that the photoelectron distribution for the observed solar spectra is significantly different from the spectrum based on Planck's radiation law. In results, the photoelectron distribution is found to be a significant function of the lunar surface potential—the photoelectron distribution in the steady state considerably differs from that of the uncharged surface. In calculations, the variation in the photoelectron distribution function with the lunar latitude, quantum yield, and work function of the surface material has been parametrically analyzed, and it is found to be sensitive to the constituent parameters.

Development of an application scheme for the SELENE/SP lunar reflectance model for radiometric calibration of hyperspectral and multispectral sensors

We have developed an application scheme for conducting lunar calibration, one of the radiometric calibration methods for optical instruments onboard Earth-orbiting satellites and planetary explorers, with a newly developed hyperspectral lunar reflectance model based on SELENE/SP data. Because the model considers photometric properties (lunar surface reflectance and its dependences on incident, emission, and phase angles) with high spectral and spatial resolution (6–8nm wavelength intervals and 0.5° grid meshes in lunar latitude and longitude), it enables us to simulate disk-resolved Moon radiance observed by not only multispectral but also hyperspectral sensors in space. Simulations of Moon observations conducted by ASTER with its three visible and near infrared bands, produced brightness profiles of simulated Moon images that show high correlation (more than 0.99) with the observed images in all bands, and the relative brightness of each pixel can be evaluated with 5% uncertainty. Consistency of dependence on phase angle and the libration effect between the SP model and another lunar reflectance model, ROLO, was also confirmed. The SP model will therefore be useful for evaluating the relative degradation of sensors in space.

Difference of brightness temperatures between 19.35 GHz and 37.0 GHz in CHANG’E-1 MRM: implications for the burial of shallow bedrock at lunar low latitude

Indications of buried lunar bedrock may help us to understand the tectonic evolution of the Moon and provide some clues for formation of lunar regolith. So far, the information on distribution and burial depth of lunar bedrock is far from sufficient. Due to good penetration ability, microwave radiation can be a potential tool to ameliorate this problem. Here, a novel method to estimate the burial depth of lunar bedrock is presented using microwave data from Chang’E-1 (CE-1) lunar satellite. The method is based on the spatial variation of differences in brightness temperatures between 19.35 GHz and 37.0 GHz (ΔTB). Large differences are found in some regions, such as the southwest edge of Oceanus Procellarum, the area between Mare Tranquillitatis and Mare Nectaris, and the highland east of Mare Smythii. Interestingly, a large change of elevation is found in the corresponding region, which might imply a shallow burial depth of lunar bedrock. To verify this deduction, a theoretical model is derived to calculate the ΔTB. Results show that ΔTB varies from 12.7 K to 15 K when the burial depth of bedrock changes from 1 m to 0.5 m in the equatorial region. Based on the available data at low lunar latitude (30°N-30°S), it is thus inferred that the southwest edge of Oceanus Procellarum, the area between Mare Tranquillitatis and Mare Nectaris, the highland located east of Mare Smythii, the edge of Pasteur and Chaplygin are the areas with shallow bedrock, the burial depth is estimated between 0.5 m and 1 m.

Dusty plasma system in the surface layer of the illuminated part of the moon

The dusty plasma system in the surface layer of the illuminated part of the Moon has been considered. The maximum height of the dust rise has been determined. It has been shown that a dead zone, where dust particles cannot rise over the surface of the Moon, is absent near a lunar latitude of 80°. The size and height distributions of dust have been determined.

Microwave Observations and Modeling of a Lunar Eclipse

Microwave observations of the Moon during the eclipse of November 28-29, 1993, are reported. Observations were made at 1.327 mm wavelength with a 12-m-aperture radio telescope. Points observed were at the lunar equator and 42° north and south lunar latitude, all near the sub-Earth meridian of lunar longitude. Brightness temperature ( T B) was observed to decrease a maximum of 25% below the pre-eclipse value of T B. Comparisons are made between our observations and previous data sets collected under similar circumstances. A thermal model has been constructed with which we calculate eclipse cooling curves that agree with our observations. From this model inferences are made about the porosity of the lunar regolith necessary to produce the observed changes in brightness temperature throughout the eclipse. The effect of rocks resting on top of the regolith on theoretical eclipse cooling curves is examined. The data are well fit with a regolith-only model that assumes a density of 1.4 g cm -3 (porosity of 59%) for the top 1 cm of regolith. Comparison of lunar high latitude with equatorial observations suggests that regolith density increases with depth within this top 1 cm. Inclusion of rocks in the model increases the amplitude of the eclipse cooling curve for a fixed regolith density, so that a regolith + rocks model fitting the data must have a lower regolith density than a regolith-only model. The regolith model described here to explain observed eclipse cooling curves is shown to be consistent with observed diurnal cooling curves reported by Low and Davidson (1965, Astrophys. J. 142, 1278-1282).

Note on the Earth-figure perturbations in the lunar theory

Thej=2 lunar ephemeris is based on a flattening of the Earth which is slightly different from the 1964 IAU recommended value. The total effects of Earth-oblateness on the analytical lunar theory are determined, and the corrections, which are about 0″.02 in lunar longitude and latitude, are derived.

Preliminary Report on a Lunar Latitude Fluctuation.

Preliminary Report on a Lunar Latitude Fluctuation.

Recent Progress of Selenography

THE most active period in the study of selenography during late years is comprised between two epochs, that of the announcement of a change in the crater Linné in the year 1866 by Dr. Schmidt, Director of the Observatory at Athens, and that of the announcement of a new crater north-west of Hyginus, by Dr, Klein, of Cologne, in the year 1877. The years elapsed between the two events above-mentioned have been characterised more or less by the manifestation of considerable interest in lunar studies, of which the projection, of a map of the moon 200 inches in diameter, to have been constructed under the auspices of the British Association for the Advancement of Science was the first indication. Of this map, four sections embracing an area of 100 square degrees of lunar latitude and longitude have been published, containing all the formations known in 1866-1868 to exist on this area, each of which is separately catalogued. Three of these sections, with catalogues, were published in the Reports of the British Association for 1866 and 1868; the fourth was published by the aid of a private subscription, in 1870. We are not aware that much use has been made of these areas and catalogues in endeavouring to ascertain if the 433 objects chronicled in them retain the characteristics they possessed in the above-mentioned years. It was a part of the duty of the Committee appointed by the Association to receive the reports of volunteer observers who undertook to examine the objects in certain subzones at stated intervals, which-resulted in the addition of several new objects to those originally published, but nothing has been effected in this direction since the Committee was not reappointed in 1868.