Galileo photometry of Apollo landing sites

As of December 1992, the Galileo spacecraft performed its second and final flyby (EM2), of the Earth-Moon system, during which it acquired Solid State Imaging (SSI) camera images of the lunar surface suitable for photometric analysis using Hapke's, photometric model. These images, together with those from the first flyby (EM1) in December 1989, provide observations of all of the Apollo landing sites over a wide range of photometric geometries and at eight broadband filter wavelengths ranging from 0.41 micron to 0.99 micron. We have completed a preliminary photometric analysis of Apollo landing sites visible in EM1 images and developed a new strategy for a more complete analysis of the combined EM1 and EM2 data sets in conjunction with telescopic observations and spectrogoniometric measurements of returned lunar samples. No existing single data set, whether from spacecraft flyby, telescopic observation, or laboratory analysis of returned samples, describes completely the light scattering behavior of a particular location on the Moon at all angles of incidence (i), emission (e), and phase angles (a). Earthbased telescopic observations of particular lunar sites provide good coverage of incidence nad phase angles, but their range in emission angle is limited to only a few degrees because of the Moon's synchronous rotation. Spacecraft flyby observations from Galileo are now available for specific lunar features at many photometric geometries unobtainable from Earth; however, this data set lacks coverage at very small phase angles (a less than 13 deg) important for distinguishing the well-known 'opposition effect'. Spectrogoniometric measurements from returned lunar samples can provide photometric coverage at almost any geometry; however, mechanical properties of prepared particulate laboratory samples, such as particle compaction and macroscopic roughness, likely differ from those on the lunar surface. In this study, we have developed methods for the simultaneous analysis of all three types of data: we combine Galileo and telescopic observations to obtain the most complete coverage with photometric geometry, and use spectrogoniometric observations of lunar soils to help distinguish the photometric effects of macroscopic roughness from those caused by particle phase function behavior (i.e., the directional scattering properties of regolith particles)

Impact Basin Deposits in the Lunar Near Side Northern High Latitudes: Galileo Earth-Moon 2 Encounter Results

Galileo Solid-State Imaging System data provide about the nature and origin of basin deposits, and modes of ejecta emplacement and ejecta mixing, including the formation of light plains deposits. The Humboldtianum basin (61N 84E; 650 km in diamter, middle Nectarian in age) deposits do not show anomalous spectral characteristics relativeto typical highlands, suggesting that the depth of excavation was relatively shallow. Initial analyses show little evidence for a strong 0.76/0.99 signature for the majority of pre-mare Imbrian-aged light plains within the basin. The linearity and angularity of the second and first ring suggest that the inner ring is the most likely candidate for the crater rim crest. One of the highest concentrations of light plains on the Moon is seen north of Imbrium, suggesting the possible presence of cryptomaria. Much of the area north of western and central Mare Frigoris shows highland spectral characteristics; however a small number of the fresh craters in the plains have stronger 0.76/0.99 ratio signatures (indicative of iron-bearing minerals, but not necessarily of basalts). SSI data indicate the extensive younger Imbrian light plains north of eastern Frigoris also show typical mature highland signatures. A small numberof the fresh craters have relatively more intense one-micron signatures, however, and a dark-halo crater with mare basalt affinities occurs in the crater Grtner. This dark-halo crater is themost conclusive evidence for the presence of cryptomare deposits beneath the light plains so far, but it does not provide information on how widespread the deposit might be. These extensive light plain deposits are not as spectrally distinctive as the cryptomaria observed in the Schiller-Schickard area southeast of Orientale, possibly due to the greater thickness of Imbrium ejecta in the northern high latitudes