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NASA NTRS2024

Detection of Hydration on Nominally Anhydrous S-Complex Main Belt Asteroids

We present the results of a survey of nominally anhydrous main belt S-complex asteroids. Thirty-three observations of 29 unique asteroids were obtained using the IRTF+SpeX instrument in prism and LXD short modes. We report for the first time that S-complex main belt asteroids have 3μm features. The majority of the observations(27 of 33)have a detectable 3μm feature that has at least 1% band depth or greater (within error), indicating the presence of hydration. Most of the asteroids have bands of 1%–2.5% depth, but a notable fraction (nine of the observations) have band depths of>5%. These band depths are comparable to those of low albedo asteroids in the middle and outer belt that have experienced aqueous alteration. We investigate the origin of the hydration, searching for correlations with orbital, physical, and circumstantial parameters. However, we do not find any strong or moderate correlations with 3μm band depth, indicating that multiple factors may be at play, including exogenic sources, primordial water, and/or solar wind implantation. Additionally, we report the mineralogies of the asteroids, derived from the prism observations.

Main Belt S-complex asteroids↗
NASA NTRS1974

Spectral reflectance systematics for mixtures of powdered hypersthene, labradorite, and ilmenite

Spectral reflectance measurements in the range from 0.4- to 2.5 microns were made for synthetic powder mixtures of a single suite of plagioclase, pyroxene, and ilmenite, which are the principal mineral phase types making up virtually all lunar surface materials studied to date. Binary and ternary data plots of the parameters albedo, band depth, and red to blue ratios versus mixture composition show how variation in the concentration of each mineral phase in a mixture affects changes in the overall reflectance spectrum of the mixture. Principal mixing effects noted are (1) the disproportionate darkening effect of opaque ilmenites and (2) the persistence, the wavelength stability, and the depth versus concentration proportionality of the 1-micron band of pyroxene. These results indicate that by comparing the albedo and band depth of an unknown spectrum with calibration data obtained with laboratory standards, it is possible to determine the ratio of crystalline phases in the material producing spectra such as may be obtained telescopically from small areas on lunar and planetary surfaces.

Nash, D. B.↗
NASA NTRS1984

Saturn's satellites - Near-infrared spectrophotometry (0.65-2.5 microns) of the leading and trailing sides and compositional implications

Water ice absorptions at 2.0, 1.5, and 1.25 microns are noted in near-IR spectra of Tethys, Dione, Rhea, Iapetus, and Hyperion, and the weak 1.04-micron ice absorption, which is detected for Rhea and Dione, is studied to establish band depth upper limits. The leading-trailing side 1.04-micron ice band depth differences on Saturn's satellites are similar to those for the Galilean satellites, indicating possible surface modification by magnetospheric charged particle bombardment. Limits are obtained for the amounts of particulates, trapped gases, and ammonium hydroxide on the surface. With the exception of the dark side of Iapetus, the surfaces of all of Saturn's satellites are nearly pure ice water.

Steele, A.↗
NASA NTRS1981

Water frost and ice - The near-infrared spectral reflectance 0.65-2.5 microns

The spectral reflectance of water frost and frost on ice as a function of temperature and grain size is presented with 1-1/2% spectral resolution in the 0.65- to 2.5-micron wavelength region. The well-known 2.0-, 1.65-, and 1.5-micron solid water absorption bands are precisely defined along with the little studied 1.25-micron band and the previously unidentified (in reflectance) 1.04-, 0.90-, and 0.81-micron absorption bands. The 1.5-microns band complex is quantitatively analyzed using a nonlinear least squares algorithm to resolve the band into four Gaussian components as a function of grain size and temperature. It is found that the 1.65-micron component, which was thought to be a good temperature sensor, is highly grain-size dependent and poorly suited to temperature sensing. Another Gaussian component appears to show a dependence of width on grain size while being independent of temperature. The relative apparent band depths are different for frost layers on ice than for thick layers of frost and may explain the apparent band depths seen in many planetary reflectance spectra.

Clark, R. N.↗
NASA NTRS1993

A comparison of telescopic and Phobos-2 ISM spectra of Mars in the short-wave near-infrared (0.76-1.02 microns)

Recent analyses of near-IR (0.76-3.16 microns) Mars surface reflectance spectra obtained by the Phobos-2 ISM instrument during early 1989 have revealed the presence of substantial variability in surface spectral properties. Strong absorption features seen in the 0.85-1.05 micron region are up to 10-15 percent deep relative to the local continuum and have been interpreted as evidence of Fe(2+) and Fe(3+) bearing minerals (pyroxenes and iron oxides, respectively). Though these observed band depths are comparable to those seen in laboratory reflectance spectra, they are up to three times larger than most previously reported band depths for Mars spectra at these wavelengths. Six regions of variable albedo and geologic setting were identified where ISM and 1988 opposition telescopic coverage either overlapped physically or sampled the same surface geologic unit. The areal sizes and positions of the regions measured telescopically were compiled by Bell et al. ISM pixels falling within these spots were averaged to produce a spatially convolved spectrum that simulates what would have been seen telescopically. To facilitate comparisons of absorption band positions and relative strengths, the convolved ISM data and the 1988 telescopic spectra were scaled to unity at 0.81 microns and are presented. The data have also been convolved to equivalent band pass normalized reflectances in the region of spectral overlap. A scatter diagram of telescopic vs. ISM reflectances is shown. The results from the investigation are discussed.

Bell, James F., III↗
NASA NTRS1983

Spectral properties of mixtures of montmorillonite and dark grains - Implications for remote sensing minerals containing chemically and physically adsorbed water

The spectral properties from 0.4 to 3 microns of montmorillonite plus dark carbon grains (called opaques) of various sizes are studied as a function of the weight fraction of opaques present. The reflectance level and band depths of the 1.4-, 1.9-, 2.2-, and 2.8-micron water and/or OH absorption features are analyzed using derived empirical relationships and scattering theory. It is found that the absorption band depths and reflectance level are a very nonlinear function of the weight fraction of opaques present but can be predicted in many cases by simple scattering theory. The 2.8-micron bound water fundamental band is the most difficult absorption feature to suppress. The overtone absorptions are suppressed a greater amount than the fundamental but are still apparent even when 10-20 wt pct opaques are present. The relationships observed and the simple scattering theory presented show that quantitative compositional remote sensing studies are feasible for surfaces containing complex mineral mixtures.

Clark, R. N.↗
NASA NTRS2021

Pluto’s Sputnik Planitia: Composition of geological units from infrared spectroscopy

We have compared spectroscopic data of Sputnik Planitia on Pluto, as acquired by New Horizons’ Linear Etalon Imaging Spectral Array (LEISA) instrument, to the geomorphology as mapped by White et al. (2017) using visible and panchromatic imaging acquired by the LOng-Range Reconnaissance Imager (LORRI) and the Multi-spectral Visible Imaging Camera (MVIC). We have focused on 13 of the geologic units identified by White et al. (2017), which include the plains and mountain units contained within the Sputnik basin. We divided the map of Sputnik Planitia into 15 provinces, each containing one or more geologic units, and we use LEISA to calculate the average spectra of the units inside the 15 provinces. Hapke-based modeling was then applied to the average spectra of the units to infer their surface composition, and to determine if the composition resulting from the modeling of LEISA spectra reflects the geomorphologic analyses of LORRI data, and if areas classified as being the same geologically, but which are geographically separated, share a similar composition. We investigated the spatial distribution of the most abundant ices on Pluto’s surface - CH4, N2, CO, H2O, and a non-ice component presumed to be a macromolecular carbon-rich material, termed a tholin, that imparts a positive spectral slope in the visible spectral region and a negative spectral slope longward of ~1.1 μm. Because the exact nature of the non-ice component is still debated and because the negative spectral slope of the available tholins in the near infrared does not perfectly match the Pluto data, for spectral modeling purposes we reference it generically as the negative spectral slope endmember (NSS endmember). We created maps of variations in the integrated band depth (from LEISA data) and areal mass fraction (from the modeling) of the components. The analysis of correlations between the occurrences of the endmembers in the geologic units led to the observation of an anomalous suppression of the strong CH4 absorption bands in units with compositions that are dominated by H2O ice and the NSS endmember. Exploring the mutual variation of the CH4 and N2 integrated band depths with the abundance of crystalline H2O and NSS endmember revealed that the NSS endmember is primarily responsible for the suppression of CH4 absorptions in mountainous units located along the western edge of Sputnik Planitia. Our spectroscopic analyses have provided additional insight into the geological processes that have shaped Sputnik Planitia. A general increase in volatile abundance from the north to the south of Sputnik Planitia is observed. Such an increase first observed and interpreted by Protopapa et al., 2017 and later confirmed by climate modeling (Bertrand et al., 2018) is expressed geomorphologically in the form of preferential deposition of N2 ice in the upland and mountainous regions bordering the plains of southern Sputnik Planitia. Relatively high amounts of pure CH4 are seen at the southern Tenzing Montes, which are a natural site for CH4 deposition owing to their great elevation and the lower insolation they are presently receiving. The NSS endmember correlates the existence of tholins within certain units, mostly those coating the low-latitude mountain ranges that are co-latitudinal with the tholin-covered Cthulhu Macula. The spectral analysis has also revealed compositional differences between the handful of occurrences of northern non-cellular plains and the surrounding cellular plains, all of which are located within the portion of Sputnik Planitia that is presently experiencing net sublimation of volatiles, and which do not therefore exhibit a surface layer of bright, freshly-deposited N2 ice. The compositional differences between the cellular and non-cellular plains here hint at the effectiveness of convection in entraining and trapping tholins within the body of the cellular plains, while preventing the spread of such tholins to abutting non-cellular plains.

Pluto's Sputnik Planitia↗
NASA NTRS2003

Hydrogen Concentrations on C-Class Asteroids Derived from Remote Sensing

We present spectroscopic observations of 16 asteroids from 1.9-3.6 microns collected from the United Kingdom Infrared Telescope (UKIRT) from 1996-2000. Of these 16 asteroids, 11 show some evidence of a 3 microns hydrated mineral absorption feature greater than 2(sigma) at 2.9 microns. Using relations first recognized for carbonaceous chondrite powders by Miyamoto and Zolensky and Sato et al., we have determined the hydrogen to silicon ratio for these asteroids and calculated their equivalent water contents, assuming all the hydrogen was in water. The asteroids split into 2 groups, roughly defined as equivalent water contents approx. greater than 7% (8 asteroids, all with 3 microns band depths approx. greater than 20%) and approx. greater than 3% for the remaining 8 asteroids. This latter group includes some asteroids for which a weak but statistically significant 3 microns band of non-zero depth exists. The G-class asteroids in the survey have higher water contents, consistent with CM chondrites. This strengthens the connection between CM chondrites and G asteroids that was proposed by Burbine. We find that the 0.7 microns and 3 microns band depths are correlated for the population of target objects.

Rivkin, A. S.↗
NASA NTRS2003

Hydrogen Concentrations on C-class Asteroids Derived from Remote Sensing

We present spectroscopic observations of 16 asteroids from 1.9-3.6 microns collected from the United Kingdom Infrared Telescope (UKIRT) from 1996-2000. Of these 16 asteroids, 11 show some evidence of a 3 micron hydrated mineral absorption feature greater than 2 sigma at 2.9 microns. Using relations first recognized for carbonaceous chondrite powders by Miyamoto and Zolensky (1994) and Sato et al. (1997), we have determined the hydrogen to silicon ratio for these asteroids and calculated their equivalent water contents, assuming all the hydrogen was in water. The asteroids split into 2 groups, roughly defined as equivalent water contents greater than approximately 7% (8 asteroids, all with 3 micron band depths greater than approximately 20%) and less than approximately 3% for the remaining 8 asteroids. This latter group includes some asteroids for which a weak but statistically significant 3 micron band of non-zero depth exists. The G-class asteroids in the survey have higher water contents, consistent with CM chondrites. This strengthens the connection between CM chondrites and G asteroids that was proposed by Burbine (1998). We find that the 0.7 micron and 3 micron band depths are correlated for the population of target objects.

Rivkin, A. S.↗
NASA NTRS2020

Weak Spectral Features on (101995) Bennu from the OSIRIS-REx Visible and InfraRed Spectrometer

Context. The NASA Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission has obtained thousands of spectra of asteroid (101955) Bennu with the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS). Aims. We present a spectral search for minor absorption bands and determine compositional variations on the surface of Bennu. Methods. Reflectance spectra with low and high spatial resolutions were analyzed for evidence of weak absorption bands. Spectra were also divided by a global average spectrum to isolate unique spectral features, and variations in the strongest band depths were mapped on a surface shape model. The global visible to near-IR spectrum of Bennu shows evidence of several weak absorption bands with depths of a few percent. Results. Several observed bands are consistent with phyllosilicates, and their distribution correlates with the stronger 2.74-μm hydration band. A 0.55-μm band is consistent with iron and is deepest in the spectrally reddest areas on Bennu. The presence of hydrated phyllosilicates and iron oxides indicates substantial aqueous alteration in Bennu’s past. Conclusions. Bennu’s spectra are not identical to a limited set of carbonaceous chondrite spectra, possibly due to compositional properties and spatial scale differences; however, returned samples should contain a mixture of common chondrite materials.

OSIRIS-REx↗
NASA NTRS1994

Quantitative reflectance spectroscopy of buddingtonite from the Cuprite mining district, Nevada

Buddingtonite, an ammonium-bearing feldspar diagnostic of volcanic-hosted alteration, can be identified and, in some cases, quantitatively measured using short-wave infrared (SWIR) reflectance spectroscopy. In this study over 200 samples from Cuprite, Nevada, were evaluated by X ray diffraction, chemical analysis, scanning electron microscopy, and SWIR reflectance spectroscopy with the objective of developing a quantitative remote-sensing technique for rapid determination of the amount of ammonium or buddingtonite present, and its distribution across the site. Based upon the Hapke theory of radiative transfer from particulate surfaces, spectra from quantitative, physical mixtures were compared with computed mixture spectra. We hypothesized that the concentration of ammonium in each sample is related to the size and shape of the ammonium absorption bands and tested this hypothesis for samples of relatively pure buddingtonite. We found that the band depth of the 2.12-micron NH4 feature is linearly related to the NH4 concentration for the Cuprite buddingtonite, and that the relationship is approximately exponential for a larger range of NH4 concentrations. Associated minerals such as smectite and jarosite suppress the depth of the 2.12-micron NH4 absorption band. Quantitative reflectance spectroscopy is possible when the effects of these associated minerals are also considered.

Felzer, Benjamin↗
NASA NTRS1999

A Proposed Landing Site for the 2001 Lander in a Hematite-Rich Region in Sinus Meridiani

The Thermal Emission Spectrometer (TES) instrument on the Mars Global Surveyor (MGS) mission has identified an accumulation of crystalline hematite (alpha-Fe2O3) that covers an area with very sharp boundaries approximately 350 by 350-750 km in size centered near 2 S latitude between 0 and 5 W longitude (Sinus Meridiani). The depth and shape of the hematite fundamental bands in the TES spectra show that the hematite is relatively coarse grained (> 5-10 microns). The spectrally-derived areal abundance of hematite varies with particle size from approx. 10% for particles > 30 microns in diameter to 40-60% for unpacked 10 micron powders. The hematite in Sinus Meridiani is thus distinct from the fine-grained (diameter < 5-10 microns), red, crystalline hematite considered, on the basis of visible and near-IR data, to be a minor spectral component in Martian bright regions. A map of the hematite index has been constructed using TES data from 11 orbits, including the six in which hematite was detected and five orbits that passed nearby that showed no evidence of hematite. The boundaries of the hematite-rich region are sharp at spatial scales of about 10 km. Within this region there are spatial variations in spectral band depth of a factor of two to three. At the present time the hematite-rich region has not been completely mapped. However, by using the bounding orbits to the east and west in which hematite was not detected, we can establish that this region covers an area that is between 350 and 750 km in length and over -350 km in width (1.2 x 10(exp 5) to 2.6 x 10(exp 5 sq km). The hematite-rich surface discovered by TES closely corresponds with smooth-surfaced unit ('sm') that appears to be the surface of a layered sequence. The presence of small mesas superposed on 'sm' and the degraded nature of the small impact craters suggests that material has been removed from this unit. These layered materials do not appear to be primary volcanic products (i.e., lava flows) because there are no associated lava flow lobes, fronts or pressure ridges; there are no fissures or calderae, nor any other features that can be interpreted as volcanic within 'sm'. Bowl-shaped depressions in 'sm' and the remnant mesas on top of a portion of this unit suggest that deflation has removed material that was once above the present surface of 'sm'. The most likely cause of the deflation is wind, which suggests that the layered materials are relatively friable. In summary, Sinus Meridiani hematite is closely associated with a smooth, layered, friable surface that is interpreted to be sedimentary in origin.

Christensen, Philip R.↗
NASA NTRS2021

Observations of Phobos and Deimos with SpeX at NASA Infrared Telescope Facility

We measured near-infrared (NIR) reflectance spectra of Phobos and Deimos, using the prism (0.7–2.52 μm) and long-wavelength cross dispersed (LXD: 1.9–4.2 μm) modes of NASA Infrared Telescope Facility (IRTF)’s SpeX instrument. The goal of this study is to investigate the surface composition of Phobos and Deimos and search for any mineralogical absorption signatures that may be present on their surfaces, especially in the LXD spectral range. Prism spectra of Phobos showed significant slope variation at shorter wavelengths (λ <1.3 μm), which indicates surface heterogeneity possibly due to regolith’s composition and grain size, and/or space weathering. Deimos’ prism spectra were found to be consistent with the more red-sloped prism spectra of Phobos. The measured LXD spectra of Deimos revealed evidence of hydration with 3-μm band depths at 2.90 μm of 4–5%. The 3-μm band in Deimos could be attributed to exogenic sources such as solar wind implantation or OH-bearingimpactors, or to an endogenic source and the presence of carbonaceous material on its surface. Phobos’ andDeimos’ prism and LXD spectra, however, show no indications for absorption signatures of mafic silicates (i.e.,pyroxene, olivine), organics nor carbonates.

D Takir↗
NASA NTRS1993

A deep envelope composition for TX Piscium?

Results of observations of the carbon star TX Psc at high resolution in the 4000/cm spectral region and at moderate resolution from 2500 to 8000/cm are reported. The opacity sampling technique is employed to present model atmospheres of carbon stars with normal solar oxygen abundance and deep envelope composition that include HCN and C2H2. The oxygen abundance of TX Psc is found to be more accurately represented by a deep envelope composition depleted in oxygen by roughly two orders of magnitude than by a solar oxygen abundance. Polyatomic opacities influence the CO line depths and the derived oxygen abundance as a second-order effect. Polyatomic bands appear to be far too strong in the models, implying the need for another source of opacity to backwarm the outer atmosphere and thereby limit the polyatomic band depths. Dust, rather than polyatomic molecules, is a candidate for the backwarming opacity.

Goebel, J. H.↗
NASA NTRS2016

Multispectral VNIR Observations by the Opportunity Rover Pancam of Multiple Episodes of Aqueous Alteration in Marathon Valley, Endeavour Crater, Mars

Since early 2015, the Mars Exploration Rover Opportunity has been exploring the break in the rim of Endeavour Crater dubbed Marathon Valley by the rover team. Marathon Valley was identified by orbital hyperspectral data from the MRO CRISM as having a relatively strong spectral feature in the 2.3 micrometer region indicative of an Mg or Fe-OH combination overtone absorption band indicative of smectite clay. Earlier in its mission, Opportunity examined the Matijevic Hill region on the more northerly Cape York crater rim segment and found evidence for smectite clays in a stratigraphically lower, pre-impact formed unit dubbed the Matijevic formation. However, the smectite exposures in Marathon Valley appear to be associated with the stratigraphically higher Shoemaker formation impact breccia. Evidence for alteration in this unit in Marathon Valley is provided by Pancam multispectral observations in the 430 to 1010 nm visible/near infrared (VNIR) spectral range. Sinuous troughs ("red zones") contain fragmented cobbles and pebbles displaying higher blue-to-red slopes, moderately higher 535 nm band depths, elevated 754 to 934 nm, and negative 934 to 1009 nm slopes. The lack of an absorption at 864 to 904 nm indicates the lack of crystalline red hematite in these red zones, but likely an enrichment in nanophase ferric oxides. The negative 934 to 1009 nm slope is potentially indicative of the presence of adsorbed or structurally bound water. A scuff in a red zone near the southern wall of Marathon Valley uncovered light-toned soils and a pebble with an 803 to 864 nm absorption resembling that of light-toned Fe-sulfate bearing soils uncovered by the Spirit rover in the Columbia Hills of Gusev crater. APXS chemical measurements indicated enrichments of Mg and S in the scuff soils and the pebble, Joseph Field, with the strongest 803 nm band- consistent with Mg and Fe sulfates. The presence of Fe and Mg sulfates can be interpreted as evidence of a potentially later episode of aqueous alteration with an earlier, neutral to alkaline pH episode forming the Fe/Mg smectites and a later acid pH episode forming the Fe and Mg sulfates.

Farrand, William H.↗
DOE OSTI2024

Impact of survey spatial variability on galaxy redshift distributions and the cosmological 3 × 2-point statistics for the Rubin Legacy Survey of Space and Time (LSST)

We investigate the impact of spatial survey non-uniformity on the galaxy redshift distributions for forthcoming data releases of the Rubin Observatory Legacy Survey of Space and Time (LSST). Specifically, we construct a mock photometry data set degraded by the Rubin OpSim observing conditions, and estimate photometric redshifts of the sample using a template-fitting photo-z estimator, BPZ, and a machine learning method, FlexZBoost. We select the Gold sample, defined as $i\lt 25.3$ for 10 yr LSST data, with an adjusted magnitude cut for each year and divide it into five tomographic redshift bins for the weak lensing lens and source samples. We quantify the change in the number of objects, mean redshift, and width of each tomographic bin as a function of the coadd i-band depth for 1-yr (Y1), 3-yr (Y3), and 5-yr (Y5) data. In particular, Y3 and Y5 have large non-uniformity due to the rolling cadence of LSST, hence provide a worst-case scenario of the impact from non-uniformity. We find that these quantities typically increase with depth, and the variation can be $10\!-\!40~{{\rm per\ cent}}$ at extreme depth values. Using Y3 as an example, we propagate the variable depth effect to the weak lensing $3\times 2$ pt analysis, and assess the impact on cosmological parameters via a Fisher forecast. We find that galaxy clustering is most susceptible to variable depth, and non-uniformity needs to be mitigated below 3 per cent to recover unbiased cosmological constraints. There is little impact on galaxy–shear and shear–shear power spectra, given the expected LSST Y3 noise.

cosmology↗
NASA NTRS1980

The composition of the Martian dark regions: Observations and analysis

Near infrared telescopic spectrophotometry for dark regions is present and interpreted using laboratory studies of iron bearing mineral mixtures and terrestrial oxidized and unoxidized basalts. Upon closer inspection (by spacecraft) the telescopic dark regions were found to consist of large scale intermixtures of bright soil (aeolian dust) and dark materials. The dark materials themselves consist of an intimate physical association of very fine grained ferric oxide bearing material with relatively high near infrared reflectance and darker, relatively unoxidized rocks or rock fragments. While these two components could exist finely intermixed in a soil, a number of lines of evidence indicate that the usual occurrence is probably a thin coating of physically bound oxidized material. The coated rocks are dark and generally clinopyroxene bearing. The shallow band depths and low overall reflectances indicate that opaque minerals such as magnetite are probably abundant.

Singer, R. B.↗
NASA NTRS1983

The Uranian satellites - Surface compositions and opposition brightness surges

The present, 5 percent-resolution spectrophotometry for the Uranian satellites Ariel, Umbriel, Titania and Oberon cover the 1.43-2.57 wavelength region and confirm the presence of a spectrally dominant water ice component in their surfaces. The 1.5- and 2.0-micron water absorption band depths and continuum reflectance indicate significant differences among the surface compositional properties of the four satellites, and comparisons of the spectra with those of other solar system bodies and of laboratory water ice spectra imply the presence of a significant nonwater ice component on/in their surfaces. The nature of this nonwater ice component is suggested by the data to be similar to that of such substances as carbon black. Near-IR opposition brightness surges of Ariel, Titania and Oberon are found to be among the largest in the solar system.

Brown, R. H.↗