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1.
The mineralogy of Mars is well understood on a qualitative level at a global scale due to satellite data. Quantitative analysis of visible and near-infrared (VNIR) satellite data is a desirable but nontrivial task, due partly to the nonlinearity of VNIR reflectance spectra from the mineral mixtures of the Martian surface. In this study, we investigated the use of the Hapke radiative transfer model to generate linearly mixed single scattering albedo data from nonlinearly mixed VNIR reflectance data and then quantitatively analyzed them using the linear spectral mixture model. Simplifications to the Hapke equation were tested accounting for variables that would be unknown when using satellite data. Mineral mixture spectra from the RELAB spectral library were degraded to test the robustness of the unmixing technique in the face of data that mimic some of the complexities of satellite spectral data collected at Mars. A final test was performed on spectra from shergottite meteorites to assess the technique against real Martian mineral mixtures. The simplified Hapke routine produced robust abundance estimates within 5–10% accuracy when applied to laboratory standard spectra from the synthetic mixtures of igneous minerals in agreement with previous studies. The results of tests involving degraded data to mimic the low spectral contrast of the Martian surface and the lack of a priori knowledge of the constituent mineral spectral endmembers, however, were less encouraging, with errors in abundance estimation greater than 25%. These results cast doubt on the utility of Hapke unmixing for the quantitative analysis of VNIR data of the surface of Mars.  相似文献   

2.
Abstract— Zagami and Nakhla are achondrites and belong to the Shergotty-Nakhla-Chassigny (SNC) meteorite group. It is generally accepted that Mars is their parent body. Mineralogical and chemical analyses have revealed that the major mineral phases of these two meteorites are pyroxene, olivine, maskelynite, and plagioclase. In this work, near-infrared biconical reflectance measurements were performed on sawed surfaces of chips from Zagami and Nakhla. Spectra obtained with an analytical spot diameter on the order of the mineral grain size reflect the heterogeneous distribution of different mineral phases. The characteristic absorption bands of the pyroxenes are numerically evaluated in terms of the modified Gaussian model. Spectra with overlapping absorption features are resolved into the basic absorption bands. From these results, it can be estimated what kind of clinopyroxenes belong to the investigated mineral assemblages. As a result, the major clinopyroxene phase in Nakhla is Ca-rich augite, whereas in Zagami both Ca-rich and Ca-poor pyroxenes are present. By means of such a procedure, laboratory spectra of minerals become more informative and may help in discussing Martian remote sensing data in the near-infrared region.  相似文献   

3.
Ted L. Roush 《Icarus》2005,179(1):259-264
Optical constants are estimated from near-infrared reflectance spectra of the smectite clay montmorillonite using an iterative combination of particulate scattering theory and Kramers-Kronig analysis. The final results provide wavelength dependent imaginary indices of refraction similar to previous studies, but in addition produce wavelength dependent real indices of refraction, unlike most previous studies. A comparison of the values derived here to those previously reported for montmorillonite shows that the maxima absorption coefficient values from the two studies are in excellent agreement, and in other wavelength regions the two studies agree to within about a factor of two. This suggests that the approach presented can provide a reliable mechanism of estimating the wavelength dependence of both the real and imaginary indices for materials at visible and near-infrared wavelengths. The resulting near-infrared values are combined with mid-infrared values of the same sample to provide optical constants of montmorillonite over the 0.66-25 μm wavelength region.  相似文献   

4.
We present near infrared reflectance spectra from 0.8 to 2.5 μm of two asteroids with low Tisserand invariant, 1373 Cincinnati and 2906 Caltech. We compare our spectra with cometary nuclei and other asteroids in their class. Asteroids Cincinnati and Caltech have Tisserand invariant values of 2.72 and 2.97, respectively, values less than 3 are considered suggestive of cometary origin. The observed spectral slopes in the near-infrared are consistent with both the spectra of cometary nuclei and of primitive asteroids. However, both asteroids have features in the near-infrared that are not seen in cometary nuclei, but are present in other X-type asteroids. 1373 Cincinnati has a sharp slope change between 0.75 and 1.0 μm and 2906 Caltech has a broad and shallow absorption between 1.35 and 2.2 μm. Our attempts to model the visible and near-infrared spectrum of these two objects, with the components successfully used by Emery and Brown (2004, Icarus 164, 104–121) to fit Trojan asteroids, did not yield acceptable fits.Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract to the National Aeronautics and Space Administration.  相似文献   

5.
Mineral compositions and abundances derived from visible/near-infrared (VIS/NIR or VNIR) spectra are used to classify asteroids, identify meteorite parent bodies, and understand the structure of the asteroid belt. Using a suite of 48 equilibrated (types 4-6) ordinary (H, L, and LL) chondrites containing orthopyroxene, clinopyroxene, and olivine, new relationships between spectra and mineralogy have been established. Contrary to previous suggestions, no meaningful correlation is observed between band parameters and cpx/(opx + cpx) ratios. We derive new calibrations for determining mineral abundances (ol/(ol + px)) and mafic silicate compositions (Fa in olivine, Fs in pyroxene) from VIS/NIR spectra. These calibrations confirm that band area ratio (BAR) is controlled by mineral abundances, while Band I center is controlled by mafic silicate compositions. Spectrally-derived mineralogical parameters correctly classify H, L and LL chondrites in ∼80% of cases, suggesting that these are robust relationships that can be applied to S(IV) asteroids with ordinary chondrites mineralogies. Comparison of asteroids and meteorites using these new mineralogical parameters has the advantage that H, L and LL chemical groups were originally defined on the basis of mafic silicate compositions.  相似文献   

6.
Roger N. Clark 《Icarus》1980,44(2):388-409
The reflectance spectra of Ganymede, Europa, Callisto, and Saturn's rings are analyzed using recent laboratory reflectance studies of water frost, water ice, and water and mineral mixtures. It is found that the spectra of the icy Galilean satellites are characteristic of water ice (e.g., ice blocks or possibly very large ice crystals ? 1 cm) or frost on ice rather than pure water frost, and that the decrease in reflectance at visible wavelengths is caused by other mineral grains in the surface. The spectra of Saturn's rings are more characteristic of water frost with some other mineral grains mixed in the frost but not on the surface. The impurities on all these objects are not in spectrally isolated patches but appear to be intimately mixed with the water. The impurity grains appear to have reflectance spectra typical of minerals containing Fe3+. Some carbonaceous chondrite meteorite spectra show the necessary spectral shape. Ganymede is found to have more water ice on the surface than previously thought (～90 wt%), as is Callisto (30–90 wt%). The surface of Europa has a vast frozen water surface with only a few percent impurities. Saturn's rings also have only a few percent impurities. The amount of bound water or bound OH for these objects is 5 ± 5 wt% averaged over the entire surface. Thus with the small amount of nonicy material present on these objects, no hydrated minerals can be ruled out. A new absorption feature is identified in Ganymede, Callisto, and probably Europa at 1.5 μm which is also seen in the spectra of Io but not in Saturn's rings. This feature has not been seen in laboratory studies and its cause is unknown.  相似文献   

7.
More than 500 images of Io in eclipse were acquired by the Cassini spacecraft in late 2000 and early 2001 as it passed through the jovian system en route to Saturn (Porco et al., 2003, Science 299, 1541-1547). Io's bright equatorial glows were detected in Cassini's near-ultraviolet filters, supporting the interpretation that the visible emissions are predominantly due to molecular SO2. Detailed comparisons of laboratory SO2 spectra with the Cassini observations indicate that a mixture of gases contribute to the equatorial emissions. Potassium is suggested by new detections of the equatorial glows at near-infrared wavelengths from 730 to 800 nm. Neutral atomic oxygen and sodium are required to explain the brightness of the glows at visible wavelengths. The molecule S2 is postulated to emit most of the glow intensity in the wavelength interval from 390 to 500 nm. The locations of the visible emissions vary in response to the changing orientation of the external magnetic field, tracking the tangent points of the jovian magnetic field lines. Limb glows distinct from the equatorial emissions were observed at visible to near-infrared wavelengths from 500 to 850 nm, indicating that atomic O, Na, and K are distributed across Io's surface. Stratification of the atmosphere is demonstrated by differences in the altitudes of emissions at various wavelengths: SO2 emissions are confined to a region close to Io's surface, whereas neutral oxygen emissions are seen at altitudes that reach up to 900 km, or half the radius of the satellite. Pre-egress brightening demonstrates that light scattered into Jupiter's shadow by gases or aerosols in the giant planet's upper atmosphere contaminates images of Io taken within 13 minutes of entry into or emergence from Jupiter's umbra. Although partial atmospheric collapse is suggested by the longer timescale for post-ingress dimming than pre-egress brightening, Io's atmosphere must be substantially supported by volcanism to retain auroral emissions throughout the duration of eclipse.  相似文献   

8.
T.L. Roush  J.B. Dalton 《Icarus》2004,168(1):158-162
We report the visible and near-infrared (0.4-2.5 μm) laboratory bidirectional reflectance of hydrated Titan tholin at cryogenic temperatures (∼100-300 K). When compared with room temperature measurements, the visible and near-infrared color of hydrated Titan tholin becomes bluer by ∼14% at low temperatures in the 0.7-1.0 μm region. Assuming the observed color changes are representative of tholin-like materials we estimate the influence of such color changes on the interpretation of the Centaur Pholus and find that the modest color changes will not significantly alter existing interpretations.  相似文献   

9.
We present near-infrared spectra of 23 B-type asteroids obtained with the NICS camera-spectrograph at the 3.56 m Telescopio Nazionale Galileo. We also compile additional visible and near-infrared spectra of another 22 B-type asteroids from the literature. A total of 45 B-types are analyzed. No significant trends in orbital properties of our sample were detected when compared with all known B-types and all known asteroids. The reflectance spectra of the asteroids in the 0.8–2.5 μm range show a continuous shape variation, from a monotonic negative (blue) slope to a positive (red) slope. This continuous spectral trend is filling the gap between the two main groups of B-types published by Clark et al. ([2010]. J. Geophys. Res., 115, 6005–6027). We found no clear correlations between the spectral slope and the asteroids’ sizes or heliocentric distances. We apply a clustering technique to reduce the volume of data to six optimized “average spectra” or “centroids”, representative of the whole sample. These centroids are then compared against meteorite spectra from the RELAB database. We found carbonaceous chondrites as the best meteorite analogs for the six centroids. There is a progressive change in analogs that correlates with the spectral slope: from CM2 chondrites (water-rich, aqueously altered) for the reddest centroid, to CK4 chondrites (dry, heated/thermally altered) for the bluest one.  相似文献   

10.
Faint absorption bands in the visible range of the smoothed vestoid spectra have been found. The bands centered near 505, 530, and 550 nm are attributed to ferrous iron in low-calcium pyroxene and are typical for pyroxene-bearing vestoid surfaces. In accordance with characteristics of the faint absorption bands around 600 and 650 nm the studied vestoid spectra can be sorted into five types. Since the same absorptions are also seen in the laboratory spectra of the minerals and meteorites, which appear to be similar to vestoid material, spectral types of the vestoids can be related to their surface compositions. Regolith of the Type-I vestoids consists of pure low-calcium pyroxenes. Minor amount of olivine along with pyroxene appear to be on the Type-II vestoids whereas the mixtures of low-calcium pyroxene with minor chromite define the Type-III and -IV. The causes for the fifth spectral type in terms of minor mineral phases are unclear now. Simulation of the spectra of vestoids was employed to estimate content of olivine (∼6-12 vol%) and chromite (∼12-30 vol%) on their surfaces.  相似文献   

11.
Space weathering is an important surface process that occurs on the Moon and other airless bodies, especially those that have no magnetic field. The optical effects of the Moon's space weathering have largely been investigated in the laboratory for lunar samples and lunar analogues. However, duplication of pristine regolith on Earth is not possible. Here we report on space weathering from the unique perspective of the "Yutu" rover, which was part of the Chang'e-3(CE-3) mission, building on our previous work.Measurement of the visually undisturbed uppermost regolith as well as locations that have been affected by rocket exhaust from the spacecraft by the Visible-Near Infrared Spectrometer(VNIS) revealed that the returned samples provide biased information about the pristine lunar regolith. The uppermost surficial regolith is much more weathered than the regolith immediately below, and the finest fraction is rich in space weathered products. These materials are very dark and attenuated throughout the visible and near-infrared(VNIR) wavelengths, hence reducing the reflectance and masking the absorption features. The effects on the spectral slope caused by space weathering are wavelength-dependent: the visible and near-infrared continuum slope(VNCS) increases while the visible slope(VS) decreases. In the visible wavelengths, the optical effects of space weathering and Ti O_2 are identical: both reduce albedo and blue the spectra. This suggests that a new Ti O_2 abundance algorithm is needed. Optical maturity indices are related to composition and hence only locally meaningful. Since optical remote sensing can only sense the uppermost few microns of regolith and since this surface tends to be very weathered, the interpretation of surface composition using optical remote sensing data needs to be carefully evaluated. Sampling the uppermost surface is suggested.  相似文献   

12.
We present reflectance spectra from 0.4 to 2.4 μm of Asteroid (101955) 1999 RQ36, the target of the OSIRIS-REx spacecraft mission. The visible spectral data were obtained at the McDonald Observatory 2.1-m telescope with the ES2 spectrograph. The infrared spectral data were obtained at the NASA Infrared Telescope Facility using the SpeX instrument. The average visible spectrum is combined with the average near-infrared wavelength spectrum to form a composite spectrum. We use three methods to constrain the compositional information in the composite spectrum of Asteroid (101955) 1999 RQ36 (hereafter RQ36). First, we perform a least-squares search for meteorite spectral analogs using 15,000 spectra from the RELAB database. Three most likely meteorite analogs are proposed based on the least-squares search. Next, six spectral parameters are measured for RQ36 and their values are compared with the ranges in parameter values of the carbonaceous chondrite meteorite classes. A most likely meteorite analog group is proposed based on the depth of overlap in parameter values. The results of the least-squares search and the parametric comparisons point to CIs and/or CMs as the most likely meteorite analogs for RQ36, and COs and CHs as the least likely. RQ36 has a spectrally “blue” continuum slope that is also observed in carbonaceous chondrites containing magnetite. We speculate that RQ36 is composed of a “CM1”-like material. Finally, we compare RQ36 to other B-type asteroids measured by Clark et al. (Clark, B.E. et al. [2010]. J. Geophys. Res. 115, E06005). The results of this comparison are inconclusive. RQ36 is comparable to Themis spectral properties in terms of its albedo, visible spectrum, and near-infrared spectrum from 1.1 to 1.45 μm. However, RQ36 is more similar to Pallas in terms of its near-infrared spectrum from 1.6 to 2.3 μm. Thus it is possible that B-type asteroids form a spectral continuum and that RQ36 is a transitional object, spectrally intermediate between the two end-members. This is particularly interesting because Asteroid 24 Themis was recently discovered to have H2O ice on the surface (Rivkin, A., Emery, J. [2010]. Nature 464, 1322–1323; Campins, H. et al. [2010a]. Nature 464, 1320–1321).  相似文献   

13.
The longstanding question of the extent to which the quasar population is affected by dust extinction, within host galaxies or galaxies along the line of sight, remains open. More generally, the spectral energy distributions of quasars vary significantly, and flux-limited samples defined at different wavelengths include different quasars. Surveys employing flux measurements at widely separated wavelengths are necessary to characterize fully the spectral properties of the quasar population. The availability of panoramic near-infrared detectors on large telescopes provides the opportunity to undertake surveys capable of establishing the importance of extinction by dust on the observed population of quasars. We introduce an efficient method for selecting K -band, flux-limited samples of quasars, termed 'KX' by analogy with the UVX method. This method exploits the difference between the power-law nature of quasar spectra and the convex spectra of stars: quasars are relatively brighter than stars at both short wavelengths (the UVX method) and long wavelengths (the KX method). We consider the feasibility of undertaking a large-area KX survey for damped Ly α galaxies and gravitational lenses using the planned UKIRT wide-field near-infrared camera.  相似文献   

14.
We report a comprehensive review of the UV–visible spectrum and rotational lightcurve of Vesta combining new observations by Hubble Space Telescope and Swift Gamma-ray Burst Observatory with archival International Ultraviolet Explorer observations. The geometric albedos of Vesta from 220 nm to 953 nm are derived by carefully comparing these observations from various instruments at different times and observing geometries. Vesta has a rotationally averaged geometric albedo of 0.09 at 250 nm, 0.14 at 300 nm, 0.26 at 373 nm, 0.38 at 673 nm, and 0.30 at 950 nm. The linear spectral slope as measured between 240 and 320 nm in the ultraviolet displays a sharp minimum near a sub-Earth longitude of 20°, and maximum in the eastern hemisphere. This is consistent with the longitudinal distribution of the spectral slope in the visible wavelength. The photometric uncertainty in the ultraviolet is ∼20%, and in the visible wavelengths it is better than 10%. The amplitude of Vesta’s rotational lightcurves is ∼10% throughout the range of wavelengths we observed, but is smaller at 950 nm (∼6%) near the 1-μm band center. Contrary to earlier reports, we found no evidence for any difference between the phasing of the ultraviolet and visible/near-infrared lightcurves with respect to sub-Earth longitude. Vesta’s average spectrum between 220 and 950 nm can well be described by measured reflectance spectra of fine particle howardite-like materials of basaltic achondrite meteorites. Combining this with the in-phase behavior of the ultraviolet, visible, and near-infrared lightcurves, and the spectral slopes with respect to the rotational phase, we conclude that there is no global ultraviolet/visible reversal on Vesta. Consequently, this implies a lack of global space weathering on Vesta, as previously inferred from visible–near-infrared data.  相似文献   

15.
Near-infrared spectra (∼0.90 to ∼1.65 μm) are presented for 181 main-belt asteroids, more than half having diameters less than 20 km. These spectra were measured using a specialized grism at the NASA Infrared Telescope Facility, where the near-infrared wavelength coverage is designed to complement visible wavelength CCD measurements for enhanced mineralogic interpretation. We have focused our analysis on asteroids that appear to have surfaces dominated by olivine or pyroxene since these objects can be best characterized with spectral coverage only out to 1.65 μm. Olivine-dominated A-type asteroids have distinctly redder slopes than olivine found in meteorites, possibly due to surface alteration effects such as micro-meteoroid bombardment simulated by laser irradiation laboratory experiments. K-type asteroids observed within the Eos family tend to be well matched by laboratory spectra of CO3 chondrites, while those independent of the Eos family have a variety of spectral properties. The revealed structure of the 1-μm band for 3628 Bo?němcová appears to refute its previously proposed match to ordinary chondrite meteorites. Bo?němcová displays a 1-μm band that is unlike that for any currently measured meteorite; however, spectra out to 2.5 μm are needed to conclusively argue that Bo?němcová has a surface mineralogy different from that of ordinary chondrites. Extending the spectral coverage of Vestoids out to ∼1.65 μm continues to be consistent with the “genetic” relationship of almost all observed Vestoids with Vesta and the howardites, eucrites, and diogenites. Eucrites/howardites provide the best spectral matches to the observed Vestoids.  相似文献   

16.
Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, M?ssbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature M?ssbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. M?ssbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water in ferric sulfate-bearing montmorillonite. Reflectance spectra of ferric sulfate-bearing montmorillonite include a strong 3-micrometers band that is more resistant to dry atmospheric conditions than the 3-micrometers band in spectra of similarly prepared ferrihydrite-bearing montmorillonites.  相似文献   

17.
Data obtained by the near-infrared spectrometer carried by the NEAR-Shoemaker spacecraft show that the spectral properties of the asteroid Eros vary with temperature. The manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface. The near-IR temperature-dependent spectral properties of Eros in the northern hemisphere, and for two individual regions on the surface, show clear evidence of the presence of the mineral olivine and are a close match to the temperature-spectral behavior of LL-type ordinary chondrite meteorites. While the presence of other olivine-rich meteorites cannot be excluded, H-type ordinary chondrites are clearly too pyroxene-rich to be permitted as a major surface component of Eros. The results of the thermal-spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of Eros.  相似文献   

18.
Photometric observations at optical and near-infrared wavelengths are presented for members of a new sample of candidate Vega-like systems, or main sequence stars with excess infrared emission due to circumstellar dust. The observations are combined with IRAS fluxes to define the spectral energy distributions of the sources. Most of the sources show only photospheric emission at near-IR wavelengths, indicating a lack of hot (∼1000 K) dust. Mid-infrared spectra are presented for four sources from the sample. One of them, HD 150193, shows strong silicate emission, while another, HD 176363, was not detected. The spectra of two stars from our previous sample of Vega-like sources both show UIR-band emission, attributed to hydrocarbon materials. Detailed comparisons of the optical and IRAS positions suggest that in some cases the IRAS source is not physically associated with the visible star. Alternative associations are suggested for several of these sources. Fractional excess luminosities are derived from the observed spectral energy distributions. The values found are comparable to those measured previously for other Vega-like sources.  相似文献   

19.
The absorption features of olivine in visible and near-infrared(VNIR) reflectance spectra are the key spectral parameters in its mineralogical studies. Generally, these spectral parameters can be obtained by exploiting the Modified Gaussian Model(MGM) with a proper continuum removal. However, different continua may change the deconvolution results of these parameters. This paper investigates the diagnostic spectral features of olivine with diverse chemical compositions. Four different continuum removal methods with MGM for getting the deconvolution results are presented and the regression equations for predicting the Mg-number(Fo#) are introduced. The results show that different continua superimposed on the mineral absorption features will make the absorption center shift, as well as the obvious alterations in shape,width and strength of the absorption band. Additionally, it is also found that the logarithm of a second-order polynomial continuum can match the overall shape of the spectrum in logarithmic space, and the improved regression equations applied to estimate the chemical composition of olivine-dominated spectra also have a better performance. As an application example, the improved approach is applied to pulse laser irradiated olivine grains to simulate and study the space weathering effects on olivine diagnostic spectral features.The experiments confirm that space weathering can make the absorption band center shift toward longer wavelength. Therefore, the Fo# estimated from remote sensing spectra may be less than its actual chemical composition. These results may provide valuable information for revealing the difference between the spectra of olivine grains and olivine-dominated asteroids.  相似文献   

20.
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