ABSTRACT Improving the constraints on the abundance of basaltic asteroids in the main asteroid belt is necessary for better understanding the thermal and collisional environment in the early solar ...system, for more rigorously identifying the genetic family for (4) Vesta, for determining the effectiveness of Yarkovsky/YORP in dispersing asteroid families, and for better quantifying the population of basaltic asteroids in the outer main belt (a > 2.5 AU) that is likely unrelated to (4) Vesta. Near-infrared (NIR) spectral observations in this work were obtained for the Vp-type asteroids (2011) Veteraniya, (5875) Kuga, (8149) Ruff, (9147) Kourakuen, (9553) Colas, (15237) 1988 RL6, (31414) Rotaryusa, and (32940) 1995 UW4 during 2014 August/September utilizing the SpeX spectrograph at the NASA Infrared Telescope Facility, Mauna Kea, Hawaii. Spectral band parameter (band centers, band area ratios) and mineralogical analysis (pyroxene chemistry) for each average asteroid NIR reflectance spectrum suggest a howardite-eucrite-diogenite meteorite analog for each asteroid. (5875) Kuga is most closely associated with the eucrite meteorites, (31414) Rotaryusa is most closely associated with the diogenites, and the remaining other six asteroids are most closely associated with the howardite meteorites. Along with their orbital locations in the inner main belt and in the vicinity of (4) Vesta, the existing evidence suggests that these eight Vp-type asteroids are also likely Vestoids.
D-type asteroids represent a complex mystery related to the accretional history, composition, and dynamical migration of Outer Solar System objects. These spectrally featureless bodies have revealed ...few clues while raising many questions over four decades. D-types are dark, difficult to observe and perhaps contain unaltered primordial material. D-type asteroids are abundant in the outer belt, dominant in the Jupiter Trojans, and rare in the inner belt as well as near Earth space. Material spectrally similar to D-types is pervasive on other outer solar system bodies as well. The appearance of dark, spectrally red material in multiple classes of small bodies suggests some unknown geochemical and/or evolutionary connection(s) may exist between them. Our investigation focused on the visible near-infrared (VNIR) (0.7–2.45 μm) spectral distinctions of D-types based on heliocentric location. Twenty-five newly acquired spectra from NASA's Infrared Telescope Facility (IRTF) plus sixty-one IRTF VNIR spectra from the literature were combined into a single database and extensively analyzed with multiple orbital, observational, and spectral variables included in the examination. Twelve of the newly acquired spectra had not been imaged previously at IRTF.
Pearson's correlation, simple and multiple regression, slope analysis, Monte Carlo modeling, as well as Principal Component Analysis (PCA) determined D-types show increased reddening with decreasing distance, with the segment from 1.5–2.45 μm, driving the overall trend for the full slope. Principal components show strong connection to the 0.7–1.35 μm slope and inclination of D-type Jupiter Trojans. Principal component combinations, magnitudes, and positive/negative direction relate strongly to both observed and derived differences in the D-type L4 and L5 Trojan population. The L5 population is less evolved spectrally and dynamically than L4 counterparts perhaps due to lower dynamical instabilities inside the L4 cloud.
•Twenty-five newly acquired D-type VNIR spectra plus sixty-one D-type spectra from the literature formed the study dataset.•D-type spectral slopes increase with decreasing semi-major axis (α) from 0.7–2.45 μm.•PCA results derived direct ties between principal components, spectral reddening, and slope.•Statistical analysis suggests PC1’ has a very significant impact on the slope segment of D-types between 0.7 and 1.35 μm.•Our study found D-type L4 Trojans and L5 Trojans exhibit significant spectral differences from each other and from main belt D-types.
Surface Composition of (99942) Apophis Reddy, Vishnu; Sanchez, Juan A.; Furfaro, Roberto ...
The Astronomical journal,
03/2018, Letnik:
155, Številka:
3
Journal Article
Recenzirano
Odprti dostop
On 2029 April 13, near-Earth asteroid (NEA) (99942) Apophis will pass at a distance of ∼6 Earth radii from Earth. This event will provide researchers with a unique opportunity to study the effects of ...tidal forces experienced by an asteroid during a close encounter with a terrestrial planet. Binzel et al. predicted that close flybys of terrestrial planets by NEAs would cause resurfacing of their regolith due to seismic shaking. In this work, we present the best pre-encounter near-infrared spectra of Apophis obtained so far. These new data were obtained during the 2013 apparition using the NASA Infrared Telescope Facility (IRTF). We found that our spectral data is consistent with previous observations by Binzel et al. but with a much higher signal-to-noise ratio. Spectral band parameters were extracted from the spectra and were used to determine the composition of the asteroid. Using a naïve Bayes classifier, we computed the likelihood of Apophis being an LL chondrite to be >99% based on mol% of Fa versus Fs. Using the same method, we estimated a probability of 89% for Apophis being an LL chondrite based on ol/(ol+px) and Fs. The results from the dynamical model indicate that the most likely source region for Apophis is the 6 resonance in the inner main belt. Data presented in this study (especially Band I depth) could serve as a baseline to verify seismic shaking during the 2029 encounter.
Investigations of the main asteroid belt and efforts to constrain that population's physical characteristics involve the daunting task of studying hundreds of thousands of small bodies. Taxonomic ...systems are routinely employed to study the large-scale nature of the asteroid belt because they utilize common observational parameters, but asteroid taxonomies only define broadly observable properties and are not compositionally diagnostic. This work builds upon the results of work by Hardersen et al., which has the goal of constraining the abundance and distribution of basaltic asteroids throughout the main asteroid belt. We report on the near-infrared (NIR: 0.7 to 2.5 m) reflectance spectra, surface mineralogical characterizations, analysis of spectral band parameters, and meteorite analogs for 33 Vp asteroids. NIR reflectance spectroscopy is an effective remote sensing technique to detect most pyroxene group minerals, which are spectrally distinct with two very broad spectral absorptions at ∼0.9 and ∼1.9 m. Combined with the results from Hardersen et al., we identify basaltic asteroids for ∼95% (39/41) of our inner-belt Vp sample, but only ∼25% (2/8) of the outer-belt Vp sample. Inner-belt basaltic asteroids are most likely associated with (4) Vesta and represent impact fragments ejected from previous collisions. Outer-belt Vp asteroids exhibit disparate spectral, mineralogical, and meteorite analog characteristics and likely originate from diverse parent bodies. The discovery of two additional likely basaltic asteroids provides additional evidence for an outer-belt basaltic asteroid population.
•Eight Vp-type mainbelt asteroids are probable Vestoids that are related to (4) Vesta.•All eight asteroids have probable analogs to the HED meteorites.•(3867) Shiretoko has a surface mineralogy ...analogous to the eucrite meteorites.•Seven asteroids have surface mineralogies analogous to the howardite meteorites.
Vestoids are generally considered to be fragments from Asteroid (4) Vesta that were ejected by past collisions that document Vesta’s collisional history. Dynamical Vestoids are defined by their spatial proximity with Vesta (Zappala, V., Bendjoya, Ph., Cellino, A., Farinella, P., Froeschle’, C. 1995. Icarus 116, 291–314; Nesvorny, D. 2012. Nesvorny HCM Asteroid Families V2.0. EAR-A-VARGBDET-5-NESVORNYFAM-V2.0. NASA Planetary Data System.). Taxonomic Vestoids are defined as V-type asteroids that have a photometric, visible-wavelength spectral, or other observational relationship with Vesta (Tholen, D.J., 1984. Asteroid Taxonomy from Cluster Analysis of Photometry. Ph.D. Thesis, University of Arizona, Tucson; Bus, S.J., Binzel, R.P. 2002. Icarus 158, 106–145; Carvano, J., Hasselmann, P.H., Lazzaro, D., Mothe’-Diniz, T. 2010. Astron. Astrophys. 510, A43). We define ‘genetic Vestoids’ as V-type asteroids that are probable fragments ejected from (4) Vesta based on the supporting combination of dynamical, near-infrared (NIR) spectral, and taxonomic evidence. NIR reflectance spectroscopy is one of the primary ground-based techniques to constrain an asteroid’s major surface mineralogy (Burns, R.G. 1993a. Mineralogical Applications of Crystal Field Theory. Cambridge University Press, Cambridge, UK, 551 p). Despite the reasonable likelihood that many dynamical and taxonomic Vestoids likely originate from Vesta, ambiguity exists concerning the fraction of these populations that are from Vesta as compared to the fraction of asteroids that might not be related to Vesta.
Currently, one of the most robust techniques to identify the genetic Vestoid population is through NIR reflectance spectroscopy from ∼0.7 to 2.5μm. The derivation of spectral band parameters, and the comparison of those band parameters with those from representative samples from the Howardite–Eucrite–Diogenite (HED) meteorite types, allows a direct comparison of their primary mineralogies. Establishing tighter constraints on the genetic Vestoid population will better inform mass estimates for the current population of probable Vestoids, will provide more accurate orbital information of Vestoid migration through time that will assist dynamical models, and will constrain the overall current abundance of basaltic material in the main asteroid belt (Moskovitz, N.A., Jedicke, R., Gaidos, E., Willman, M., Nesvorny, D., Fevig, R. 2008. Icarus 198, 77–90).
This work reports high-quality NIR spectra, and their respective interpretations, for eight Vp-type asteroids, as defined by Carvano et al. (Carvano, J., Hasselmann, P.H., Lazzaro, D., Mothe’-Diniz, T. 2010. Astron. Astrophys. 510, A43), that were observed at the NASA Infrared Telescope Facility on January 14, 2013 UT. They include: (3867) Shiretoko, (5235) Jean-Loup, (5560) Amytis, (6331) 1992 FZ1, (6976) Kanatsu, (17469) 1991 BT, (29796) 1999 CW77, and (30872) 1992 EM17. All eight asteroids exhibit the broad ∼0.9- and ∼1.9-μm mineral absorption features indicative of pyroxene on each asteroid’s surface. Data reduction and analysis via multiple techniques produced consistent results for the derived spectral absorption band centers and average pyroxene surface chemistries for all eight asteroids (Reddy, V., Sanchez, J.A., Nathues, A., Moskovitz, N.A., Li, J.-Y, Cloutis, E.A., Archer, K., Tucker, R.A., Gaffey, M.J., Mann, P.J., Sierks, H., Schade, U. 2012c. Icarus 217, 153–168; Lindsay, S.S., Emery, J.P., Marchis, F., Enriquez, J., Assafin, M. 2013. A spectroscopic and mineralogic study of multiple asteroid systems. American Astronomical Society, DPS Meeting #45, #112.04; Lindsay, S.S., Marchis, F., Emery, J.P., Enriquez, J.E., Assafin, M. 2014. Icarus, submitted for publication; Gaffey, M.J., Cloutis, E.A., Kelley, M.K., Reed, K.L. 2002. Mineralogy of asteroids. In: Bottke Jr., W.F., Cellino, A., Paolicchi, P., Binzel, R.P. (Eds.), Asteroids III. The University of Arizona Press, Tucson, pp. 183–204; Burbine, T.H., Buchanan, P.C., Dolkar, T., Binzel, R.P. 2009. Met. Planet. Sci. 44, 1331–1341.). (3867) Shiretoko is most consistent with the eucrite meteorites while the remaining seven asteroids are most consistent with the howardite meteorites. The existing evidence suggests that all eight of these Vp-type asteroids are genetic Vestoids that probably originated from Vesta’s surface.
The first verifiable near-infrared absorption features in the ∼0.9-μm spectral region are reported for Asteroids 16 Psyche, 69 Hesperia, 110 Lydia, 125 Liberatrix, 201 Penelope, and 216 Kleopatra. ...These weak features (
∼
1
–
3
%
) are attributed to orthopyroxenes present on the surfaces of these asteroids. 16 Psyche and 125 Liberatrix have full rotational coverage while 69 Hesperia, 110 Lydia, 201 Penelope, and 216 Kleopatra have
∼
75
%
rotational coverage. Qualitative ∼2-μm absorption features are present, but are very weak (
<
1
%
). Absorption band positions suggest relatively low abundances of calcium and iron in the pyroxenes. This indicates relatively reducing redox conditions for these asteroids, their parent bodies, and the nebular regions in which they formed. Four potential interpretations for these asteroids include: (1) they are exposed metallic cores or core fragments of differentiated parent bodies with residual orthopyroxene mantle material, (2) they are the result of a smelting-like reaction that converts olivine to pyroxene and metallic iron in the presence of carbon at high temperatures, (3) they are analogs to the primitive metal-rich Bencubbinite meteorites, or (4) they represent metallic surfaces which have accumulated silicate debris from external sources. Of the two original interpretations for the M-asteroids, the enstatite chondrite interpretation (Chapman and Salisbury, 1973, Icarus 19, 507–522; Gaffey and McCord, 1979, Mineralogical and petrological characterizations of asteroids. In: Gehrels T. (Ed.), Asteroids. Univ. of Arizona Press, Tucson, pp. 688–723) can be eliminated for these asteroids because the pyroxene in enstatite chondrites is iron-free and does not exhibit such absorption features. The iron meteorite interpretation remains valid, but with modification. For M-Asteroids 16 Psyche and 216 Kleopatra, these spectral results combined with previous determinations of high radar albedos indicate that these bodies are most probably exposed core fragments of differentiated bodies. M-Asteroids 69 Hesperia, 110 Lydia, 125 Liberatrix, and 201 Penelope exhibit similar spectral features consistent with exposed core fragments, but radar observations would be needed to confirm a high metal abundance. Observations of M-Asteroids 136 Austria and 325 Heidelberga suggest the absence of absorption features in the ∼0.4- to ∼2.5-μm region within the scatter of the data. Verification of the presence or absence of features across the surfaces of these two asteroids requires full rotational coverage. The interpretations for these “featureless” M-asteroids are not well-constrained, but remain consistent with the iron meteorite and enstatite chondrite interpretations.
► We studied composition of near-Earth Asteroid 2008 EV5. ► It is potential target for Marco Polo-R and Hayabusa-2 mission proposals. ► Composition is similar to a dark carbonaceous chondrite ...dominated surface. ► A weak 0.48-μm spin-forbidden Fe3+ absorption band has been detected. ► Most plausible meteorite analog is CI chondrite such as Orgueil.
We observed Potentially Hazardous Asteroid (PHA) 2008 EV5 in the visible (0.30–0.92μm) and near-IR (0.75–2.5μm) wavelengths to determine its surface composition. This asteroid is especially interesting because it is a potential target for two sample return mission proposals (Marco Polo-R and Hayabusa-2) and human exploration due to its low delta-v for rendezvous. The spectrum of 2008 EV5 is essentially featureless with exception of a weak 0.48-μm spin-forbidden Fe3+ absorption band. The spectrum also has an overall blue slope. The albedo of 2008 EV5 remains uncertain with a lower limit at 0.05 and a higher end at 0.20 based on thermal modeling. The Busch et al. (Busch et al. 2011. Icarus 212, 649–660) albedo estimate of 0.12±0.04 is consistent with our thermal modeling results. The albedo and composition of 2008 EV5 are also consistent with a C-type taxonomic classification (Somers, J.M., Hicks, M.D., Lawrence, K.J. 2008. Bull. Am. Astron. Soc. 40, 440). The best spectral match is with CI carbonaceous chondrites similar to Orgueil, which also have a weak 0.48-μm feature and an overall blue slope. This 0.48-μm feature is also seen in the spectrum of magnetite. The albedo of CI chondrites is at the lower limit of our estimated range for the albedo of 2008 EV5.
Spectral reflectance properties of ureilites CLOUTIS, E. A.; HUDON, Pierre; ROMANEK, Christopher S. ...
Meteoritics & planetary science,
October/November 2010, Letnik:
45, Številka:
10-11
Journal Article
Recenzirano
Odprti dostop
– The 0.35–2.6 μm reflectance spectra of 18 ureilites have been examined in order to improve our understanding of the spectral reflectance properties of this meteorite class. Across this spectral ...range, ureilite spectra are characterized by a steep rise in reflectance over the 0.3 to approximately 0.7 μm range, low overall reflectance (<25%) and weak mafic iron silicate absorption bands in the 1 and 2 μm region. The weakness of these bands and the low reflectance are attributed to the presence of dispersed graphite and related carbonaceous phases, metal, and possibly shock. Wavelength positions of the mafic silicate absorption bands span a range of values, but are consistent with the presence of pyroxene and olivine. Ureilite spectra generally exhibit blue slopes across the 0.7–2.6 μm interval and exhibit many overall similarities to some carbonaceous chondrites. The weak features and spectral diversity of ureilites make reflectance spectroscopy‐based identification of a ureilite parent body challenging. As terrestrial alteration of ureilites is prevalent, spectral studies of falls are most useful for determining the spectral properties of likely parent bodies.
•Olivine+metal spectra affected by olivine composition, metal content, grain size, nanophase iron.•Different spectral metrics can be used to constrain these properties.•Olivine±metal-bearing ...asteroids show spectral variations indicating diverse mineralogy.
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 characterized 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 assemblages 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 1μm region is resolvable in intimate mixtures for metal abundances as high as ∼90wt.%. The wavelength position of the 1μm region olivine absorption band center is sensitive to Fa content but insensitive to other variables. However, the band minimum position moves to shorter wavelengths with increasing metal abundance due to changes in spectral slope. The full width at half maximum (FWHM) of this band and reflectance at 1.8μm are both most sensitive to olivine Fa content, metal abundance, and grain size, and much less to the presence of nanophase iron that reddens spectra. Reflectance at 0.56μm and the 1.8/0.56μm reflectance ratio are sensitive to these same parameters as well as to nanophase iron-associated spectral reddening. The wavelength position of the local reflectance maximum in the 0.7μm region moves to longer wavelengths with increasing metal abundance and is most useful for constraining metal abundance in high metal-content mixtures. Pallasite slab spectra differ in a number of respects from powdered assemblages and multiple spectral parameters can be used to discriminate them. The spectra of increasingly fine-grained olivine+metal assemblages and those involving low-Fa olivine show increasing spectral dominance by metal. Systematic application of multiple spectral metrics allows olivine+metal assemblage properties such as Fa content, olivine/metal ratio, and grain size to be quantified or constrained. Analysis of reflectance spectra of 22 presumed olivine±metal-rich asteroids indicates that most of them possess low- to medium-Fa content olivine (Fa<∼67), with variable abundances of macroscopic metal. A number exhibit visible region absorption bands that are indicative of some fraction of coarser-grained olivine (>45μm). Most asteroid spectra can be plausibly linked to specific olivine±metal-bearing meteorite classes. Most of the asteroid spectra examined exhibit some degree of spectral reddening below ∼1.8μm which is most consistent with the presence of fine-grained nanophase iron, likely produced by space weathering.
► We observed 12 near-Earth asteroids to constrain their albedo, diameter and composition using their near-infrared spectrum. ► Our albedo and diameter estimates are consistent with those obtained by ...thermal-IR and radar observations. ► Composition of the asteroids we observed ranges from low albedo carbonaceous chondrites to bright enstatite achondrites.
We present a method to constrain the albedo and diameters of near-Earth asteroids (NEAs) based on thermal flux in their near-infrared spectra (0.7–2.5μm) using the Standard Thermal Model. Near-infrared spectra obtained with the SpeX instrument on NASA Infrared Telescope Facility are used to estimate the albedo and diameters of 12 NEAs (1992 JE, 1992 UY4, 1999 JD6, 2004 XP14, 2005 YY93, 2007 DS84, 2005 AD13, 2005 WJ56, 1999 JM8, 2005 RC34, 2003 YE45, and 2008 QS11). Albedo estimates were compared with average albedo for various taxonomic classes outlined by Thomas et al. (Thomas, C.A. et al. 2011. Astron. J. 142(3)) and are consistent with their results. Spectral band parameters, like band centers, are derived and compared to spectra of laboratory mineral mixtures and meteorites to constrain their composition and possible meteorite analogs. Based on our study we estimate the albedos and diameters of these NEAs and compare them with those obtained by other techniques such as ground-based mid-infrared, Spitzer thermal infrared and Arecibo radar. Our results are broadly consistent with the results from other direct methods like radar. Determining the compositions of low albedo asteroids is a challenge due to the lack of deep silicate absorption features. However, based on weak absorption features and albedo, we suggest possible meteorite analogs for these NEAs, which include black chondrites, CM2 carbonaceous chondrites and enstatite achondrites. We did not find any specific trends in albedo and composition among the asteroids we observed.
PDF
