ALBERT

Description: During the Galileo spacecraft encounter with the Earth-Moon system in December, 1992, a variety of spectral data and imagery were obtained for the eastern limb region as well as much of the lunar nearside. In order to support this encounter, we have been collecting near-infrared spectra and other remote sensing data for that portion of the northeastern nearside (NEM region) for which the highest resolution Galileo data were obtained. Analysis of spectra obtained for highlands units in the NEN region indicates that most surface units are dominated by anorthositic norite. To date, no pure anorthosites have been identified in the region. Several dark-haloed impact craters have exposed mare material from beneath highlands-rich surface units. Hence, ancient mare volcanism occurred in at least a portion of the NEN region. Endogenic dark-haloed craters in the region are the source of localized dark mantle deposits (LDMD) of pyroclastic origin and at least two compositional groups are present. The Galileo spacecraft obtained very high-resolution remote sensing data for the northeastern part of the nearside of the Moon. In order to prepare for and support this encounter, we have collected and analyzed a variety of spectral data for the NEN region. Numerous unanswered questions exist for this region. These include: (1) the composition and stratigraphy of the local highlands crust, (2) the nature and mode of formation of regional light plains, (3) the composition of localized pyroclastic deposits, and (4) the distribution of possible cryptomare in the region. The purpose of this paper is to present the preliminary results of our analyzes of remote sensing data of remote sensing data obtained for the NEN region.

Description: Remote sensing studies of lunar basin and crater deposits were conducted in order to determine the composition of surface units and to investigate the stratigraphy of the lunar crust. These studies have combined both visible and near-IR spectral observations with multispectral imaging in order to determine the lithology of relatively small portions (2-10 km) of the lunar surface. Numerous deposits of pure anorthosite (plagioclase greater than 90 percent) were identified and an interesting pattern has emerged. The purposes of this report are as follows: (1) to summarize the results of our previous studies of the distribution of anorthosite; (2)to present new findings concerning the modes of occurrence of lunar anorthosite; and (3) to assess the implication for the magma ocean hypothesis.

Description: The region of the moon near the border between Mare Serenitatis and Mare Tranquillitatis is one of the most geologically and compositionally complex areas of the nearside. The geologic history of this region has been shaped by impacts of widely-varying spatial scale and temporal occurrence, by volcanism of variable style and composition with time, and by limited tectonism. We have been studying this region as part of a larger multi remote sensing technique effort to understand the composition, morphology, geology, and stratigraphy of the moon at spatial scales of 2 km or less. The effort has been aided by the proximity of this area to the Apollo 11, 15, and 17 landing sites and by the occurrence of one of the primary lunar spectroscopic 'standard areas' within our scene (MS2). Here, some of the findings from the multispectral imaging and spectroscopy part of this effort are reported.

Description: Lunar pyroclastic deposits represent one of the primary anticipated sources of raw materials for future human settlements. These deposits are fine-grained volcanic debris layers produced by explosive volcanism contemporaneous with the early stage of mare infilling. There are several large regional pyroclastic units on the Moon (for example, the Aristarchus Plateau, Rima Bode, and Sulpicius Gallus formations), and numerous localized examples, which often occur as dark-halo deposits around endogenic craters (such as in the floor of Alphonsus Crater). Several regional pyroclastic deposits were studied with spectral reflectance techniques: the Aristarchus Plateau materials were found to be a relatively homogeneous blanket of iron-rich glasses. One such deposit was sampled at the Apollo 17 landing site, and was found to have ferrous oxide and titanium dioxide contents of 12 percent and 5 percent, respectively. While the areal extent of these deposits is relatively well defined from orbital photographs, their depths have been constrained only by a few studies of partially filled impact craters and by imaging radar data. A model for radar backscatter from mantled units applicable to both 70-cm and 12.6-cm wavelength radar data is presented. Depth estimates from such radar observations may be useful in planning future utilization of lunar pyroclastic deposits.

Description: In recent years, we have utilized the Apollo orbital geochemistry datasets and Earth-based spectral reflectance data to investigate the composition of highland units associated with lunar multiring basins. These include Imbrium, Orientale, and Nectaris Basins. We have also analyzed a large number of near-IR reflectance spectra and multispectral images in an attempt to answer a variety of questions concerning the Serenitatis Basin. These questions include the following: (1) What is the composition of highland units in the region and how do these compositions vary as a function of position around and distance from Serenitatis?; (2) What was the crustal stratigraphy of the Serenitatis preimpact target site?; (3) How do the Apollo 17 samples relate to geologic units in the surrounding highlands?; (4) What is the nature and origin of light plains deposits in the region?; and (5) Do cryptomare occur in the Serenitatis region? The purpose of this paper is to present the preliminary results of our analyses of spectral data obtained for the Serenitatis Basin region.

Description: A portion of the mare-bounding (MB) ring of Humorum Basin is composed of pure anorthosite while other parts of the ring are composed of noritic anorthosite. An episode of mare volcanism emplaced basaltic units in the region northwest of the MB ring after the Humorum impact event. Subsequently, large impacts emplaced a veneer of highlands material atop the basalt flows. Some mare material could have been mixed with this highlands debris either by local mixing by secondary craters or by vertical mixing. Spectra for most other highlands units in the region indicate a noritic anorthosite lithology. Spectra of mare basalts in Mare Humorum and nearby mare flooded craters show relatively deep absorption bands due to the presence of abundant high-Ca pyroxene. An analysis of spectra for a small number of craters in the highlands west of the outer ring of Humorum reveals the presence of high-Ca pyroxene. This suggests the possible presence of an extensive gabbroic province.

Description: Near-IR reflectance spectra (0.6-2.5 microns) and CCD images in the extended visible range (0.4-1.0 microns) obtained with Earth-based telescopes have been used to investigate the composition and origin of formations in the Schiller-Schickard region of the Moon. Of particular interest are the Schickard light plains, which represent an area of mantled mare basalt, or cryptomare. Here local pre-existing mare basalts were eroded and incorporated into a highlands-rich deposit by eject a from the Orientale Basin. Spectra observations of mature and immature highland and mare surfaces, as well as dark-halo crater materials provide information on the mafic mineralogy of features in the area. Analyses of the '1 micron' absorption band and spectral mixing models indicate that selected spots in the light plains contain on the order of 50 percent mare basalt. CCD image cubes can be used to map the amount of basalt in the light plains and evaluate changes with radial distance from Orientale.

Description: Multispectral imaging in the visible and near-IR at four wavelengths (0.73, 0.96, 1.45, and 1.99 micron) of Copernicus crater has been used to map the distribution of olivine-rich, pyroxene-poor material known previously to occur in the central peak complex. Three additional portions of the crater exhibit spectral characteristics similar to those of the central peaks, strongly suggesting the presence of material similar to that exposed in the central peaks. These areas are a scarp forming a portion of the northern rim of Copernicus, and two slump blocks in the north wall which may have been derived from the same portion of the ejecta now exposed in the rim scarp. These occurrences decrease the minimum allowable depth for this unusual material in the Copernicus target site though still represent some of the deepest material exposed by Copernicus.