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  • 1
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    Mercury: Mid-infrared (7.3 - 13.5 microns) spectroscopic observations showing features characteristic of plagioclase (1994)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Mid-infrared spectroscopic observations of the surface of Mercury are reported for the wavelength range 7.3 to 13.5 microns. The observed spectral radiance emanated from equatorial and low latitude regions between 110-130 deg Mercurian longitude. The area is primarily an intercrater plain. The spectra show distinct and recognizable features, the principal Christiansen emission peak being the most prominent. The Christiansen feature strongly suggests the presence of plagioclase (Ca,Na)(Al,Si)AlSi2O8, (in particular labradorite: Ab(50) - Ab(30)). In addition we have studied the effects of thermal gradients to gain insight into the effects of thermal conditions on the spectral radiance of rock samples. This simulates the thermophysical effects as the rotating surface of Mercury is alternately heated and cooled. The spectral features of the samples are retained; however, the relative and absolute amplitudes vary as illustrated by laboratory reflectance and emittance spectra from quartzite.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., The Twenty-Fifth Lunar and Planetary Science Conference. Part 2: H-O; p 739-740
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  • 2
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    The moon - Mid-infrared (7.5- to 11.4-microns) spectroscopy of selected regions (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Scaled spectral emissivity spectra have been obtained from five locations on the illuminated lunar surface and are interpreted in terms of differences in their mineralogic composition. The emission maximum, which typically falls near 8.0 microns for lunar rocks and fines, is observed to be shifted from 7.9 microns for noritic Copernicus crater walls to 8.1 microns for the olivine-rich central peak. Two mare locations show the emission maximum centered at 8.0 microns, consistent with laboratory emission measurements of basalts. An emissivity minimum at 10.5 microns in the spectrum from central peak 2 is attributed to the presence of olivine. Minima centered at 8.75 microns in the crater wall spectra resemble minima in laboratory spectra from pyroxene. A broad minimum centered at 8.5 microns in the Kepler ejecta spectrum and a sharp drop in emissivity at wavelengths longer than 11 microns in spectra from both mare locations suggest plagioclase.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 100; 1; p. 73-84.
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  • 3
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    The sodium and potassium atmosphere of the moon and its interaction with the surface (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Results are presented from Apollo satellite observations (from May 1988 to July 1991) of sodium and potassium in the lunar atmosphere. The observations of Na and K show a wide range of scale heights, single-component temperatures, and surface number densities, while the column abundances remain within a factor of 3. The observed trends can be explained using a model of competing release mechanisms with different dependences on solar zenith angle and resulting two-component atmospheres. The theory is applied to the budget of atomic oxygen.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 96; 27-42
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  • 4
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    Determination of rock type on Mercury and the moon through remote sensing in the thermal infrared (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Thermal infrared emission spectra of the moon and Mercury have been obtained using the Si:As photoconductor and circular variable filter at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Lunar spectra from 7.2 to 12.2 microns for two different locations in the south polar highlands have Christiansen frequency peaks at 8.1 microns and 7.9 microns, respectively. This indicates different compositions at the two locations; mafic in the first case, more felsic in the second. Emission spectra from Mercury are not as spatially localized,; however, the longitude of maximum contribution to the spectrum can be calculated from thermal models of the earth-facing disk. Results for areas centered at two longitudes have been obtained. Two locations in the intercrater plains were observed. At 40-deg longitude (very near the crater Homer), a peak at 7.9 microns indicates mafic igneous rock type. Spectra emanating from 46-deg longitude have peaks at 7.8 microns, indicating a region borderline between mafic and intermediate composition.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 808-811
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  • 5
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    Observations of sodium in the tenuous lunar atmosphere (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Spectra showing the sodium D lines above the moon's bright limb (subsolar point) were obtained at first and last quarters, May 27 and June 7, 1988. The number density at the surface is 57 + or - 20 atoms/cu cm and the scale height is 79 + or - 8 km, compatible with the temperature of the surface. Comparison with the Mercurian density of 26,000 atoms/cu cm reveals an enigma. Despite the apparent general similarity of the surfaces, the sodium densities are in a ratio of about 400. The difference may be attributed to differences in source or loss mechanisms or to some fundamental compositional difference between the two planets. The possibility that the source is rapid diffusion of sodium through Mercury's crust and regolith is discussed, as well as recent observational evidence that Mercury's regolith is of intermediate rock type and may be more sodium-rich than the moon's.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 15; 1141-114
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  • 6
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    Observations of potassium in the tenuous lunar atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observations of neutral potassium (K) in the tenuous lunar atmosphere are described. An echelle spectrograph, CCD, and data acquisition system are used to obtain emission spectra of neutral K atoms in the lunar atmosphere as observed by the 1.54 telescope at the Catalina Observatory at first quarter the night of April 29, 1989. A table of relevant lunar atmosphere parameters summarizes the results of the investigation. It is found that the number density at the surface is 9.5 + or - 1 atoms per cu cm and that there is a large nonthermal component and a deficiency of atoms equilibrated to the surface temperature. The calculated thermalization rate of the nonthermal component through encounters with the lunar surface gives a source of strength for the thermal component factor of 7 greater than loss by photoionization. Possible explanations for the low thermalized population observed are considered.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 2253-225
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  • 7
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    Caloris Basin - An enhanced source for potassium in Mercury's atmosphere (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Enhanced abundances of neutral K in the atmosphere of Mercury have been found above the longitude range containing Caloris Basin. Results of a large data set including six elongations of the planet between June 1986 and January 1988 show typical K column abundances of about 5.4 x 10 to the 8th K atmos/sq cm. During the observing period in October 1987, when Caloris Basin was in view, the typical K column was about 2.7 x 10 to the 9th K atoms/sq cm. Another large value was seen over the Caloris antipode in January 1988. This enhancement is consistent with an increased source of K from the well-fractured crust and regolith associated with this large impact basin. The phenomenon is localized because at most solar angles, thermal alkali atoms cannot move more than a few hundred kilometers from their source before being lost to ionization by solar ultraviolet radiation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 249; 1140-114
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