Yunzhao Wu

Mineralogical variation of the late stage mare basalts

The last major phases of lunar volcanism occurred mainly in Oceanus Procellarum and Mare Imbrium and produced spectrally unique medium- and high-titanium basalts. The composition and distribution of these basalts provide a record of the late stage thermal evolution of the Moon. To study the spectral and mineralogical variations of the late stage mare basalts, 31 distinct units were mapped employing a range of remote sensing data. Their inferred mineralogical characteristics were studied by analyzing the spectral features of small, fresh craters derived from the Moon Mineralogy Mapper (M3) data. The strongest olivine spectral signatures were found around Lichtenberg crater, while the units with the lowest olivine/pyroxene ratio occurred mainly in the southern Kepler crater and some local areas. In Oceanus Procellarum, the olivine/pyroxene ratio decreases progressively from the Lichtenberg crater to the southern units. The northern and southern units within Mare Imbrium have higher olivine/pyroxene ratios than the central ones. The inferred abundance of olivine appears to vary stratigraphically, with the younger flows being more olivine rich. However, the stratigraphically younger units around Euler crater in Mare Imbrium, which present as dark red hues in the integrated band depth image of M3, were found to have lower olivine/pyroxene ratios than the units around Lichtenberg crater (shown as light red hues) in Oceanus Procellarum. It could be interpreted that the late stage mare basalts around Lichtenberg crater originated from a more olivine-rich source than those around Euler crater.

Effect of Topography Degradation on Crater Size‐Frequency Distributions: Implications for Populations of Small Craters and Age Dating

Whether or not background secondary craters dominate populations of small impact craters on terrestrial bodies is a half-century controversy. It has been suggested that small craters on some planetary bodies are dominated by background secondary craters based partly on the steepened slope of crater size-frequency distribution (CSFD) towards small diameters, such as the less than ~1 km diameter crater population on the lunar mare. Here we show that topography degradation enlarges craters and increases CSFD slopes with time. When topography degradation is taken into account, for various-aged crater populations, the observed steep CSFD at small diameters is uniformly consistent with an originally shallower CSFD, whose slope is undifferentiated from the CSFD slope estimated from near-Earth objects and terrestrial bolides. The results show that the effect of topography degradation on CSFD is important in dating planetary surfaces, and the steepening of CSFD slopes is not necessarily caused by secondary cratering, but rather a natural consequence of topography degradation.

Study of the continuum removal method for the Moon Mineralogy Mapper（M^3） and its application to Mare Humorum and Mare Nubium

The absorption band center of visible and near infrared reflectance spectra is a key spectral parameter for lunar mineralogical studies, especially for the mafic minerals (olivine and pyroxene) of mare basalts, which have two obvious absorption bands at 1000 nm (Band I) and 2000 nm (Band II). Removal of the continuum from spectra, which was developed by Clark and Roush and used to isolate the particular absorption feature, is necessary to estimate this parameter. The Moon Mineralogy Mapper (M 3 ) data are widely used for lunar mineral identification. However, M 3 data show a residual thermal effect, which interferes with the continuum removal, and systematic differences exist among optical data taken during different optical periods. This study investigated a suitable continuum removal method and compared the difference between two sets of M 3 data taken during different optical periods, Optical Period 1B (OP1B) and Optical Period 2A (OP2A). Two programs for continuum removal are reported in this paper. Generally, a program respectively constructs two straight lines across Band I and Band II to remove the continuum, which is recommended for locating band centers, because it can find the same Band I center with different right endpoints. The optimal right endpoint for continuum removal is mainly dominated by two optical period data at approximately 2480 and 2560 nm for OP1B and OP2A data, respectively. The band center values derived from OP1B data are smaller than those derived from OP2A data in Band I but larger in Band II, especially for the spectra using longer right endpoints (>2600 nm). This may be due to the spectral slopes of OP1B data being steeper than those of OP2A data in Band I but gentler in Band II. These results were applied to Mare Humorum and Mare Nubium, and the measurements were found to mainly vary from intermediate- to high-Ca pyroxene.

Submicroscopic metallic iron in lunar soils estimated from the in situ spectra of the Chang'E-3 mission: First In Situ Estimates of SMFE in Lunar Soils

…This research was supported by the National High Technology Research and Development Program of China (863 Program: 2015AA123704), the National Natural Science Foundation of China (41422110 and 41490633), the Science and Technology Development Fund of Macau (020/2014/A1), and Minor Planet Foundation of Purple Mountain Observatory. The contribution of D.T.B. was made possible by the Chinese Academy of Sciences President’s International Fellowship Initiative, grant 2015VEB057 and by NASA Lunar Data Analysis Program grant NNX16AN55G. E.A.C. thanks NSERC and the Canadian Space Agency for supporting this study.