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  • LUNAR AND PLANETARY EXPLORATION  (8)
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  • 1
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    Determination of lunar ilmenite abundances from remotely sensed data (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The mineral ilmenite (FeTiO3) was found in abundance in lunar mare soils returned during the Apollo project. Lunar ilmenite often contains greater than 50 weight-percent titanium dioxide (TiO2), and is a primary potential resource for oxygen and other raw materials to supply future lunar bases. Chemical and spectroscopic analysis of the returned lunar soils produced an empirical function that relates the spectral reflectance ratio at 400 and 560 nm to the weight percent abundance of TiO2. This allowed mapping of the lunar TiO2 distribution using telescopic vidicon multispectral imaging from the ground; however, the time variant photometric response of the vidicon detectors produced abundance uncertainties of at least 2 to 5 percent. Since that time, solid-state charge-coupled device (CCD) detector technology capable of much improved photometric response has become available. An investigation of the lunar TiO2 distribution was carried out utilizing groundbased telescopic CCD multispectral imagery and spectroscopy. The work was approached in phases to develop optimum technique based upon initial results. The goal is to achieve the best possible TiO2 abundance maps from the ground as a precursor to lunar orbiter and robotic sample return missions, and to produce a better idea of the peak abundances of TiO2 for benefaction studies. These phases and the results are summarized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA Space Engineering Research Center for Utilization of Local Planetary Resources; 6 p
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  • 2
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    Storm on Saturn (1991)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: In September 1990, a white spot appeared on Saturn's atmosphere, which later spread over the entire equatorial region. The accompanying images were obtained as part of an effort to refine techniques for obtaining high resolution groundbased charge coupled device (CCD) images of the planets, and show the turbulent disturbance in Saturn's atmosphere. These broad red-band CCD images were obtained in November 1990 with the Catalina 1.5 m telescope. The planet was low in the sky at sunset, but the viewing was good enough to show detail in the equatorial region over all longitudes. Visibility of the features is enhanced by digital spatial filtering techniques. A storm of this magnitude has not been seen on Saturn since 1933.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Astronomy, 1991; p 169
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  • 3
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    Evaluation of the sensitivity of reflectance ratios to mafic minerals in the lunar regolith (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The 950/560-nm spectral ratio has been traditionally used as a qualitative indicator or lunar soil maturity because the 950-nm band falls within the major Fe(2+) mineral absorption bands near 1-micron characteristic of relatively immature crystalline surfaces. Since there are several other processes unrelated to maturation that may affect this ratio value, the 950/730-nm ratio has been evaluated as a potentially better measure of the relative 1-micron band strength. It is found that the 950/730-nm ratio appears to be much more sensitive to the 1-micron band depth, but it is believed that other unknown variables preclude using these single ratios to provide meaningful quantitative results at this time.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 2149-215
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  • 4
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    Remote sensing of potential lunar resources. I - Near-side compositional properties (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Using telescopic CCD multispectral images of the lunar near side and the results of 330-870 nm spectroscopy of selected regions, the compositional differences relevant to the locations of potential lunar resources (such as ilmenite, FeTiO3, and solar-wind-implanted He-3 and H) are estimated. The 400/560 nm CCD ratio images were converted to weight percent TiO2, and the values were used to construct a new TiO2 abundance map which can be used to estimate the areas potentially rich in ilmenite. A 950/560 nm CCD ratio mosaic of the full moon provides estimates of relative surface maturity. Since high He-3 concentrations correlate with mature ilmenite-rich soils, a combination of relative surface maturity maps and the TiO2 abundance maps can be used to estimate distributions of He-3 (and possibly H) on local scales.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 18
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  • 5
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    A reevaluation of spectral ratios for lunar mare TiO2 mapping (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The empirical relation established by Charette et al. (1974) between the 400/560-nm spectral ratio of mature mare soils and weight percent TiO2 has been used extensively to map titanium content in the lunar maria. Relative reflectance spectra of mare regions show that a reference wavelength further into the near-IR, e.g., above 700 nm, could be used in place of the 560-nm band to provide greater contrast (a greater range of ratio values) and hence a more sensitive indicator of titanium content. An analysis of 400/730-nm ratio values derived from both laboratory and telescopic relative reflectance spectra suggests that this ratio provides greater sensitivity to TiO2 content than the 400/560-nm ratio. The increased range of ratio values is manifested in higher contrast 400/730-nm ratio images compared to 400/560-nm ratio images. This potential improvement in sensivity encourages a reevaluation of the original Charette et al. (1974) relation using the 400/730-nm ratio.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 2153-215
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  • 6
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    Structure and particle properties of Saturn's E Ring (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The present systematic reanalysis of a substantial portion of extant photometric data on the Saturn E Ring has calibrated every observation on the basis of a common 3D model. A simple power-law model is found to describe the ring's normal optical depth profile with orbital radius; this trend is departed from, however, near the density peak, where there emerges a 30-percent localized decrease in thickness. No power-law size distribution is found to be compatible with available photometry. The peculiar size distribution points to a ring origin in a process that was not collisional or disruptive.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 94; 451-473
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  • 7
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    Ferric iron in primitive asteroids - A 0.43-micron absorption feature (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A search of reflectance spectra of C- P-, D- and S-class asteroids to hunt for the Soret band near 0.4 micron that is indicative of porphyrins yielded an identification of an 0.43 micron absorption feature in 11 primitive asteroids of the C, P, and G classes and in one S-class asteroid. It is proposed that the feature is an Fe(3+) spin-forbidden transition in aqueously altered material, possibly located near 0.43 micron due to an enhancement effect similar to the mechanism operating in jarosite. The significance of the feature for the aqueous alteration history of these asteroids is addressed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 102; 2; p. 225-231.
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  • 8
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    Remote sensing of potential lunar resources. 2: High spatial resolution mapping of spectral reflectance ratios and implications for nearside mare TiO2 content` (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: High spatial resolution maps illustrating variations in spectral reflectance 400/560 nm ratio values have been generated for the following mare regions: (1) the border between southern Mare Serenitatis and northern Mare Tranquillitatis (including the MS-2 standard area and Apollo 17 landing site), (2) central Mare Tranquillitatis, (3) Oceanus Procellarum near Seleucus, and (4) southern Oceanus Procellarum and Flamsteed. We have also obtained 320-1000 nm reflectance spectra of several sites relative to MS-2 to facilitate scaling of the images and provide additional information on surface composition. Inferred TiO2 abundances for these mare regions have been determined using an empirical calibration which relates the weight percent TiO2 in mature mare regolith to the observed 400/560 nm ratio. Mare areas with high TiO2 abundances are probably rich in ilmenite (FeTiO3) a potential lunar resource. The highest potential TiO2 concentrations we have identified in the nearside maria occur in central Mare Tranquillitatis. Inferred TiO2 contents for these areas are greater than 9 wt% and are spatially consistent with the highest-TiO2 regions mapped previously at lower spatial resolution. We note that the morphology of surface units with high 400/560 nm ratio values increases in complexity at higher spatial resolutions. Comparisons have been made with previously published geologic maps, Lunar Orbiter IV, and ground-based images, and some possible morphologic correlatins have been found between our mapped 400/560 nm ratio values and volcanic landforms such as lava flows, mare domes, and collapse pits.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; E3; p. 5,601-5,619
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