[Show abstract][Hide abstract] ABSTRACT: We utilize surface temperature measurements and ultraviolet albedo spectra from the Lunar Reconnaissance Orbiter to test the hypothesis that exposed water frost exists within the Moon’s shadowed polar craters, and that temperature controls its concentration and spatial distribution. For locations with annual maximum temperatures greater than the H2O sublimation temperature of ∼110 K, we find no evidence for exposed water frost, based on the LAMP UV spectra. However, we observe a strong change in spectral behavior at locations perennially below ∼110 K, consistent with cold-trapped ice on the surface. In addition to the temperature association, spectral evidence for water frost comes from the following spectral features: a) decreasing Lyman-α albedo, b) decreasing “on-band” (129.57 - 155.57 nm) albedo, and c) increasing “off-band” (155.57 - 189.57 nm) albedo. All of these features are consistent with the UV spectrum of water ice, and are expected for water ice layers > ∼100 nm in thickness. High regolith porosity, which would darken the surface at all wavelengths, cannot alone explain the observed spectral changes at low temperatures. Given the observed LAMP off-band/on-band albedo ratios at a spatial scale of 250 m, the range of water ice concentrations within the cold traps with < 110 K is ∼0.1 - 2.0% by mass, if the ice is intimately mixed with dry regolith. If pure water ice is exposed instead, then up to ∼10% of the surface area on the 250-m scale of the measurements may be ice-covered. The observed distribution of exposed water ice is highly heterogeneous, with some cold traps < 110 K having little to no apparent water frost, and others with a significant amount of water frost. As noted by Gladstone et al. (2012), this heterogeneity may be a consequence of the fact that the net supply rate of H2O molecules to the lunar poles is very similar to the net destruction rate within the cold traps. However, an observed increase in apparent H2O abundance with decreasing temperature from ∼110 K to 65 K suggests that destruction of surface frosts by impact gardening and space weathering is spatially heterogeneous. We find a loosely bimodal distribution of apparent ice concentrations with temperature, possibly due to competition between vertical mixing by impact gardening and resupply of H2O by vapor diffusion at sites ∼110 K. Finally, we cannot rule out the possibility that the colder population of ice deposits is in fact primarily carbon dioxide ice, although peak temperatures of ∼65 K are slightly higher than the usual CO2 sublimation temperature of ∼60 K.
[Show abstract][Hide abstract] ABSTRACT: Mineralogical measurements from spectral remote sensing and remote geochemical measurements from gamma-ray and neutron spectrometers are complementary data sets that have been used together successfully to study the distributions of iron, titanium, and rare earth elements on the Moon. We compare neutron and gamma-ray data sets from Lunar Prospector and find them in good agreement with each other within the errors of previously developed equations that relate neutron flux with geochemistry, but find small adjustments to the nominal values are warranted. We used the neutron-validated LP GRS oxides to improve Clementine-based global mineral maps. The comparison was enabled by converting the minerals of Lucey (2004) to oxides using stoichiometry and assumptions about Mg#, calcium content of clinopyroxenes, and An#. We find that FeO and Al2O3 derived from the maps of Lucey (2004) do not follow the expected negative correlation seen in lunar samples, but can be brought into agreement with samples and with LP GRS oxides by increasing plagioclase in proportion with orthopyroxene abundance, while simultaneously decreasing Mg#. We interpreted this to mean that plagioclase and orthopyroxene exist in rocks together (as in a noritic rock) with the spectrally difficult to detect plagioclase being masked by the strong spectral signature of the orthopyroxene. We generated a revised set of maps of the major lunar minerals and a map of Mg# for the mafic minerals that are consistent with Lunar Prospector neutron and gamma-ray spectrometer results and show greatly improved agreement with lunar soil samples over previous global mineral maps from Clementine.
American Mineralogist 04/2015; 100(4):973-982. DOI:10.2138/am-2015-4874 · 2.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ryder and Wood (1977) suggested that the lunar crust becomes more mafic with depth because the impact melts associated with the large Imbrium and Serenitatis basins are more mafic than the surface composition of the Moon. In this study, we re-examine the hypothesis that the crust becomes more mafic with depth; we analyze the composition of crater central peaks by using recent remote sensing data and combining the best practices of previous studies. We compute the mineralogy for 34 central peaks using: (1) nine band visible and near-infrared data from the Kaguya Multiband Imager, (2) an improved version of Hapke's radiative transfer model validated with spectra of lunar soils with well-known modal mineralogy, and (3) new crustal thickness models from the Gravity Recovery and Interior Laboratory (GRAIL) data to examine the variation in composition with depth. We find that there is no increase in mafic mineral abundances with proximity to the crust/mantle boundary, or with depth from the current lunar surface, and therefore that the crust does not become more mafic with depth. We find that anorthosite with very low mafic abundance (" purest anorthosite" or PAN, Ohtake et al., 2009) is a minority constituent in these peaks and there is no clear evidence of a distinct PAN-rich layer in the middle crust as previously proposed. The composition of most of the central peaks we analyze is more mafic than classically defined anorthosites (Stöffler et al., 1980) with an average noritic anorthosite composition similar to that of the lunar surface.
[Show abstract][Hide abstract] ABSTRACT: The possibility of lunar polar ice was suggested by Harold Urey in the 1950's , and has likely been directly detected at the North Pole of Mercury by MESSENGER. That detection was based on the presence of reflectance anomalies seen by the Mercury Laser Altimeter (MLA) that occurred only where models of the surface temperature allow long-duration preservation of surface water ice against sublimation [2,3]. Anomalous reflectance is also seen at the lunar poles, revealed by laser measurements. The reflectance of permanently shadowed regions is systematically higher than nearby areas that receive at least some illumination [2,3,4] (Fig. 1). Models suggest that if the higher reflectance is due to the presence of water ice; up to 14 wt.% could be present depending on the distribution of frost within or on the regolith. Results of lunar observations by the Deep Impact High-Resolution Instrument – Infrared spectrometer (HRI-IR) in the 3 μm region and by the Lunar Recon-naissance Orbiter (LRO) Lyman Alpha mapping pro-ject (LAMP) in the far-UV region both show that spectral features consistent with hydration of the surface are diurnally variable. This indicates that water is possibly mobile on the lunar surface [5,6]. Because the lifetime of water molecules in the lunar atmosphere is short against dissociation (~20 hours) compared to the lunar diurnal cycle, water must be continuously produced to account for the observations. Mobile water will trap on cold surfaces during the lunar night and be released when surfaces are illuminated during the day. In this study, we seek evidence for transient water frost on the polar surfaces using reflectance data from the Lunar Orbiter Laser Altimeter (LOLA), and temperature data from the DIVINER radiometer, both onboard the LRO. We aim to search for areas that may “load” with surface frost during the night causing in-creased reflectance, and unload during the day reducing the reflectance. Detection of transient surface frost constrains the rate of input into the lunar volatile system.
46th Lunar and Planetary Science Conference, The Woodlands; 03/2015
[Show abstract][Hide abstract] ABSTRACT: Lunar swirls are high-albedo markings on the Moon that occur in both mare and highland terrains; their origin remains a point of contention. Here, we use data from the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer to support the hypothesis that the swirls are formed as a result of deflection of the solar wind by local magnetic fields. Thermal infrared data from this instrument display an anomaly in the position of the silicate Christiansen Feature consistent with reduced space weathering. These data also show that swirl regions are not thermophysically anomalous, which strongly constrains their formation mechanism. The results of this study indicate that either solar wind sputtering and implantation are more important than micrometeoroid bombardment in the space-weathering process, or that micrometeoroid bombardment is a necessary but not sufficient process in space weathering, which occurs on airless bodies throughout the solar system.
[Show abstract][Hide abstract] ABSTRACT: In the recent Mars 2020 Rover Science Definition Team Report, the National Aeronautics and Space Administration (NASA) has sought the capability to detect and identify elements, minerals, and most importantly, biosignatures, at fine scales for the preparation of a retrievable cache
of samples. The current Mars rover, the Mars Science Laboratory Curiosity, has a remote laser-induced breakdown spectroscopy (LIBS) instrument, a type of quantitative elemental analysis, called the Chemistry Camera (ChemCam) that has shown that laser-induced spectroscopy instruments
are not only feasible for space exploration, but are reliable and complementary to traditional elemental analysis instruments such as the Alpha Particle X-Ray Spectrometer. The superb track record of ChemCam has paved the way for other laser-induced spectroscopy instruments, such as Raman
and fluorescence spectroscopy. We have developed a prototype remote LIBS‐Raman‐fluorescence instrument, Q-switched laser-induced time-resolved spectroscopy (QuaLITy), which is approximately 70 000 times more efficient at recording signals than a commercially available
LIBS instrument. The increase in detection limits and sensitivity is due to our development of a directly coupled system, the use of an intensified charge-coupled device image detector, and a pulsed laser that allows for time-resolved measurements. We compare the LIBS capabilities of our system
with an Ocean Optics spectrometer instrument at 7 m and 5 m distance. An increase in signal-to-noise ratio of at least an order of magnitude allows for greater quantitative analysis of the elements in a LIBS spectrum with 200‐300 μm spatial resolution at 7 m, a Raman instrument capable
of 1 mm spatial resolution at 3 m, and bioorganic fluorescence detection at longer distances. Thus, the new QuaLITy instrument fulfills all of the NASA expectations for proposed instruments.
[Show abstract][Hide abstract] ABSTRACT: Olivine-rich asteroids appear to be common in the main asteroid belt as well as present in the near-Earth asteroid population. There are a number of meteorite classes that are dominated by olivine ± metal. To determine whether relationships exist between these asteroids and meteorites, we spectrally character-ized a number of olivine + meteoritic metal powder intimate and areal mixtures, pallasite slabs, and olivine powders on a metal slab. Our goal is to understand the spectral characteristics of olivine + metal assem-blages and develop spectral metrics that can be used to analyze reflectance spectra of olivine-dominated asteroids. We found that the major olivine absorption band in the 1 lm region is resolvable in intimate mixtures for metal abundances as high as $90 wt.%. The wavelength position of the 1 lm region olivine
[Show abstract][Hide abstract] ABSTRACT: A global spectral survey of 4506 immature craters with diameters <1 km was carried out using near-IR data from the Kaguya
Spectral Profiler to characterize the composition of the lunar megaregolith. On the basis of band minima and radiative transfer
mixing models, small crater spectra fall into three groups: (1) mare basalts with strong absorptions at relatively long wavelengths
indicating high ratios of high- to low-Ca pyroxene; (2) norites containing about 50% plagioclase and with pyroxene assemblages
dominated by low-Ca pyroxene that occur within the South Pole-Aitken Basin (SPA), near Apollo 14 and other locations near
Imbrium Basin, and three major cryptomaria deposits; and (3) noritic anorthosites occurring within the Feldspathic Highlands
Terrane containing about 20 wt% pyroxene with a pyroxene assemblage containing exclusively very low-Ca pyroxene. Very few
pure anorthosites are present in this survey and there are no occurrences of pyroxene-poor olivine-rich assemblages. Models
of the composition of basin ejecta incorporate large amounts of mantle material and the spectral results require that that
the sampled mantle is orthopyroxenite. Basin depth-diameter ratios used in the models required to match the measured composition
are consistent with prior estimates for the largest basins. The composition found in the SPA and Imbrium regions are consistent
with mafic impact melt breccias or basaltic impact melts of basin origin. For SPA we model this composition and find it requires
an extremely low impact angle. While this is consistent with prior work on an oblique impact for the SPA event, a more robust
solution invokes the production of norite in impact melt seas.
American Mineralogist 11/2014; 99(11-12):2251-2257. DOI:10.2138/am-2014-4854 · 2.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Lunar Orbiter Laser Altimeter (LOLA) measures the backscattered energy of the returning altimetric laser pulse at its wavelength of 1064 nm, and these data are used to map the reflectivity of the Moon at zero phase angle with a photometrically-uniform data set. Global maps have been produced at 4 pixels per degree (about 8 km at the equator) and 2-km resolution within 20 degrees latitude of each pole. The zero-phase geometry is insensitive to lunar topography, so these data enable characterization of subtle variations in lunar albedo, even at high latitudes where such measurements are not possible with the Sun as the illumination source. The geometric albedo of the Moon at 1064 nm was estimated from these data with absolute calibration derived from the Kaguya Multiband Imager and extrapolated to visual wavelengths. The LOLA estimates are within 2σ of historical measurements of geometric albedo. No consistent latitude-dependent variations in reflectance are observed, suggesting that solar wind does not dominate space-weathering processes that modify lunar reflectance. The average normal albedo of the Moon is found to be much higher than that of Mercury consistent with prior measurements, but the normal albedo of the lunar maria is similar to that of Mercury suggesting a similar abundance of space weathering products. Regions within permanent shadow in the polar-regions are found to be more reflective than polar surfaces that are sometimes illuminated. Limiting analysis to data with slopes less than ten degrees eliminates variations in reflectance due to mass wasting and shows a similar increased reflectivity within permanent polar shadow. Steep slopes within permanent shadow are also more reflective than similar slopes that experience at least some illumination. Water frost and a reduction in effectiveness of space weathering are offered as possible explanations for the increased reflectivity of permanent shadow; porosity is largely ruled out as the sole explanation. The south polar crater Shackleton is found to be among the most reflective craters in its size range globally, but is not the most reflective, so mass wasting cannot be ruled out as a cause for the crater's anomalous reflectance. Models of the abundance of ice needed to account for the reflectance anomaly range from 3 to 14 % by weight or area depending on assumptions regarding the effects of porosity on reflectance and whether ice is present as patches or is well-mixed in the regolith. If differences in nanophase iron abundances are responsible for the anomaly, the permanently shadowed regions have between 50 and 80% the abundance of nanophase iron in mature lunar soil.
The Journal of Geophysical Research Planets 07/2014; DOI:10.1002/2013JE004592 · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The primary payload on the University of Hawaii-built 'HiakaSat' micro-satellite will be the Space Ultra Compact Hyperspectral Imager (SUCHI). SUCHI is a low-mass (<9kg), low-volume (10x10x36 cm(3)) long wave infrared hyperspectral imager designed and built at the University of Hawaii. SUCHI is based on a variable-gap Fabry-Perot interferometer employed as a Fourier transform spectrometer with images collected by a commercial 320x256 microbolometer array. The microbolometer camera and vacuum-sensitive electronics are contained within a sealed vessel at 1 atm. SUCHI will collect spectral radiance data from 8 to 14 microns and demonstrate the potential of this instrument for geological studies from orbit (e. g. mapping of major rock-forming minerals) and volcanic hazard observation and assessment (e. g. quantification of volcanic sulfur dioxide pollution and lava flow cooling rates). The sensor has been integrated with the satellite which will launch on the Office of Responsive Space ORS-4 mission scheduled for 2014. The primary mission will last 6 months, with extended operations anticipated for approximately 2 years. A follow-on mission has been proposed to perform imaging of Earth's surface in the 3-5 micron range with a field of view of 5 km with 5.25 m sampling (from a 350 km orbit). The 19-kg proposed instrument will be a prototype sensor for a constellation of small satellites for Earth imaging. The integrated satellite properties will be incorporated into the Hawaii Space Flight Laboratory's constellation maintenance software environment COSMOS (Comprehensive Open-architecture Space Mission Operations System) to ease future implementation of the instrument as part of a constellation.
[Show abstract][Hide abstract] ABSTRACT: Chemical micro-imaging is a powerful tool for the detection and identification of analytes of interest against a
cluttered background (i.e. trace explosive particles left behind in a fingerprint). While a variety of groups have
demonstrated the efficacy of Raman instruments for these applications, point by point or line by line acquisition of a
targeted field of view (FOV) is a time consuming process if it is to be accomplished with useful spatial resolutions.
Spectrum Photonics has developed and demonstrated a prototype system utilizing long wave infrared hyperspectral
microscopy, which enables the simultaneous collection of LWIR reflectance spectra from 8-14 μm in a 30 x 7 mm
FOV with 30 μm spatial resolution in 30 s. An overview of the uncooled Sagnac-based LWIR HSM system will be
given, emphasizing the benefits of this approach. Laboratory Hyperspectral data collected from custom mixtures
and fingerprint residues is shown, focusing on the ability of the LWIR chemical micro-imager to detect chemicals of
interest out of a cluttered background.
[Show abstract][Hide abstract] ABSTRACT: Fourier transform spectroscopy is a widely employed method for obtaining visible and infrared spectral imagery, with
applications ranging from the desktop to remote sensing. Most fielded Fourier transform spectrometers (FTS) employ the
Michelson interferometer and measure the spectrum encoded in a time-varying signal imposed by the source spectrum
interaction with the interferometer. A second, less widely used form of FTS is the spatial FTS, where the spectrum is
encoded in a pattern sampled by a detector array.
Recently we described using a Fabry-Perot interferometer, with a deliberately wedged gap geometry and engineered
surface reflectivities, to produce an imaging spatial FTS. The Fabry-Perot interferometer can be much lighter and more
compact than a conventional interferometer configuration, thereby making them suitable for portable and handheld
applications. This approach is suitable for use over many spectral regimes of interest, including visible and infrared
regions. Primary efforts to date have focused on development and demonstration of long wave infrared (LWIR) spectral
The LWIR version of the miniaturized Fabry-Perot has been shown to be effective for various applications including
spectral imaging-based chemical detection. The compact LWIR spectral imager employs uncooled optics and a
microbolometer camera; a handheld version is envisioned for future development. Recent advancements associated with
the spatial Fourier Transform imaging spectrometer system are described.
[Show abstract][Hide abstract] ABSTRACT: Mineral maps derived from the Kaguya Multiband Imager of lunar crater central peaks are augmented using Diviner CF maps to better represent plg/pyx/olv abundances.