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Composition, Mineralogy, and Porosity of Multiple Asteroid Systems from Visible and Near-infrared Spectral Data
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... [107][108][109][110][111][112] These two features, often referred to as band I and band II for the 1-and 2-μm bands, respectively, are commonly used to determine mineralogy (olivine-to-pyroxene ratio) and composition (molar percent of Fe in olivine and pyroxene) of S-complex and V-type asteroids via band parameter analysis studies. 21,105,[111][112][113][114][115][116][117] ...
... There have also been suggestions of spectral variability due to surface heterogeneity for other asteroids, but it is likely that these variations are caused by observational effects, such as viewing aspect or poor observing conditions, or different data reduction methods. 105,112 However, as mentioned previously, there are many reasons to expect spectral variability on the surfaces of asteroids. Therefore, it is likely the dearth of confirmed spectral variations due to surface heterogeneity is a result of the reliance on ground-based facilities for VNIR spectroscopy of a large population of asteroids. ...
... The Earth's atmosphere can also obscure the spectrum near 1.4 and 1.9 μm (not shown). The generic S-and V-type asteroid spectra (from Ref. 105) exhibit the 1-and 2-μm bands used to determine mafic mineralogy and compositions (see Sec. 5.3). The vertical gray bar highlights the spectral gap from 1.0 to 1.3 μm in the current Twinkle design. ...
2019 Society of PhotoOptical Instrumentation Engineers (SPIE). Twinkle is an upcoming 0.45-m space-based telescope equipped with a visible and two near-infrared spectrometers covering the spectral range 0.4 to 4.5 μm with a resolving power R 250 (λ < 2.42 μm) and R 60 (λ > 2.42 μm). We explore Twinkle's capabilities for small bodies science and find that, given Twinkle's sensitivity, pointing stability, and spectral range, the mission can observe a large number of small bodies. The sensitivity of Twinkle is calculated and compared to the flux from an object of a given visible magnitude. The number, and brightness, of asteroids and comets that enter Twinkle's field of regard is studied over three time periods of up to a decade. We find that, over a decade, several thousand asteroids enter Twinkle's field of regard with a brightness and nonsidereal rate that will allow Twinkle to characterize them at the instrumentation's native resolution with SNR > 100. Hundreds of comets can also be observed. Therefore, Twinkle offers researchers the opportunity to contribute significantly to the field of Solar System small bodies research.
... Extending mineralogical studies from specific parent asteroid to general populations requires linking asteroid reflectance properties to their mineral abundance and chemistry. Several authors (Lindsay et al., 2015;Dunn et al., 2010a;Popescu et al., 2012) have published methods to extract mineral chemistry and abundance from ordinary chondrite reflectance spectra, but minimal effort has been made to verify which of these methods accurately reproduce laboratory X-ray diffraction measurements (Dunn et al., 2010a). ...
... The Fa, Fs and olivine/pyroxene abundance were compared using four different methods to determine which method could best estimate the mineralogy with respect to Dunn et al. (2010a) published XRD values. These methods include the Sanchez et al. (2015) method with a 2nd polynomial order which successfully reproduced Dunn et al. (2010a) Band I center and Band Area Ratio values, SARA by Lindsay et al. (2015), M4AST by Popescu et al. (2012), and the method by Dunn et al. (2010a). ...
... (c) Spectrally-derived olivine to pyroxene ratio calculated by the M4AST method. To account for this underestimation, we came up with correction factors for the Sanchez et al. (2015) method, SARA (Lindsay et al., 2015) and M4AST (Popescu et al., 2012) that can be applied when using Dunn et al. (2010aDunn et al. ( , 2010b)'s chemistry equations. We use a 4th order polynomial for the Sanchez et al. (2015) method because most asteroid observers use higher order fits to extract band centers instead of 2nd order fits. ...
Ordinary chondrites comprise a significant fraction (~75%) of meteorites that fall on the Earth. A key goal in small body science is to link meteorites to their parent bodies in order to understand their formation conditions early in our Solar System history. Dunn et al. (2010a) provided a robust set of equations for deriving olivine/pyroxene chemistry and abundance ratio from visible and near-infrared (0.35–2.5 μm) spectra of silicate-rich asteroids. These equations were calibrated to X-ray diffraction (XRD) and electron microprobe measurements as ground truth for the spectrally derived values. The small body community employs a range of methods to extract spectral band parameters from telescopic spectra of S-/Q-type asteroids and use the Dunn et al. (2010a) equations to constrain mineral chemistry and abundance. The goal of this work is to understand how the changing of polynomial order and method of extracting spectral band parameters from spectra of ordinary chondrite meteorites affects the precision of derived olivine and pyroxene chemistry and abundance compared with laboratory XRD and microprobe values. Based on our analysis, we find that 2nd order polynomials provide good agreement with the linear relationship found by Dunn et al. (2010a), but with a systematic offset. We also find that Band I center values derived from differing polynomial orders cannot be used for extracting mineral chemistry with Dunn et al. (2010a) equations. We find that the Band Area Ratio (BAR) values are independent of polynomial order and the olivine to pyroxene abundance ratio extracted from BAR is immune to changing polynomial order. Of the four published methods for extracting spectral band parameters (Sanchez et al. 2015, Dunn et al. 2010a, Spectral Analysis Routine for Asteroids, or SARA, Modeling for Asteroids, or M4AST), Dunn et al. (2010a)'s method most successfully reproduces both olivine and pyroxene chemistry, followed by Sanchez et al. (2015). SARA most successfully reproduces the olivine to pyroxene abundance ratio, very closely followed by the other three methods. We find systematic underestimation of ordinary chondrite Band I centers compared to Dunn et al. (2010a) and the resulting chemistry derived from them. To account for this underestimation, we have developed a correction factor for band parameters extracted using other methods that must be added to Band I centers for asteroids that fall in H, L, LL chondrite zones when using Dunn et al. (2010a) equations.
... These two features, often referred to as Band I and Band II for the 1 and 2µm bands, respectively, are commonly used to determine mineralogy (olivine-to-pyroxene ratio) and composition (molar percent Fe in olivine and pyroxene) of S-complex and V-type asteroids via band parameter analysis studies (e.g. [22,33,49,73,67,84,7,36,58]). ...
... The Earth's atmosphere can also obscure the spectrum near 1.4 and 1.9µm (not shown). The generic Sand V-type asteroid spectra (from [49]) exhibit the 1 and 2µm bands used to determine mafic mineralogy and compositions (see Section 5.3). The vertical grey bar highlights the spectral gap from 1.0 -1.3µm in the current Twinkle design. ...
... To date, rotational variability in VNIR spectra of asteroids has been observed from in-situ spacecraft measurements for 951 Gaspra, Ida and Dactyl by Galileo [88,89], 433 Eros by NEAR [90], 4 Vesta from the Dawn spacecraft [68] and ground-based observations [32], as well as for a handful of NEOs. There have also been suggestions of spectral variability due to surface heterogeneity for other asteroids, but it is likely that these variations are caused by observational effects, such as viewing aspect or poor observing conditions, or different methodologies in data reduction methods [73,49]. However, as mentioned previously there are many reasons to expect spectral variability on the surfaces of asteroids. ...
Twinkle is an upcoming 0.45m space-based telescope equipped with a visible and two near-infrared spectrometers over the spectral range 0.4 - 4.5$\mu$m with a resolving power R $\sim$ 250 ($\lambda$\textless 2.42$\mu$m) and R $\sim$ 60 ($\lambda$\textgreater 2.42$\mu$m). Here we explore Twinkle's capabilities for small bodies science and find that, given Twinkle's sensitivity, pointing stability, and spectral range, Twinkle could observe a large number of small bodies. The sensitivity of Twinkle is calculated and compared to the flux from an object of a given visible magnitude. The number, and brightness, of asteroids and comets which enter Twinkle's field of regard is studied over three time periods of up to a decade. We find that, over a decade, several thousand asteroids enter Twinkle's field of regard with a brightness and non-sidereal rate which would allow Twinkle to characterise them at the instrumentation's native resolution with SNR \textgreater 100. Hundreds of comets could also be observed. Therefore, Twinkle offers a unique opportunity to contribute to the field of Solar System small bodies research.
... Visible wavelength spectral reduction followed standard procedures with several modifications that are attributable to the fabrication of the Goodman instrument, one due to a problem regarding quartz flat-field calibration, and another due to an effect that produces considerable fringing longward of ∼0.65 µm (see Lindsay et al., 2015). In brief, standard reduction procedures are performed using a custom IDL-based routine that includes: (1) extraction from 2D spectra to 1D spectra by summing pixels in the data range and subtracting the background value (median of column outside of data range) for each column, (2) cleaning the spectra by the rejection of anomalous pixel detections (5-σ outliers) using an 100 pixel box iterative step method, (3) shifting the cleaned asteroid and LSA star spectra to a common reference and co-adding to produce combined asteroid and LSA star frames, (4) dividing the asteroid co-added frame by the LSA star co-added frame to calculate the final relative reflectance values for each spectrum, and (5) wavelength calibration using Hg-and Ar-lamp spectral frames. ...
... The aforementioned fringing effects longward of ∼0.65 µm are corrected by the application of a Fast Fourier Transform (FFT) routine prior to co-addition and wavelength calibration, which isolates the fringing frequencies. See Lindsay et al. (2015) regarding a more detailed treatment of this routine. ...
... The spectral band parameters of S-complex Hungaria background asteroids were measured using the same methods as in HI (Lucas et al., 2017). Briefly, we used the IDL-based algorithm Spectral Analysis Routine for Asteroids or SARA 12 (Lindsay et al., 2015) to measure the band parameters [Band I and II centers, depths, areas, and band area ratio (BAR) = Band II area/Band I area] of S-type (and two A-type) Hungaria background asteroids. This algorithm normalizes the broad Band I and II absorptions by fitting 5th order polynomials to the absorption band shoulders, fitting linear continua tangentially to the shoulders, and dividing by the continua. ...
Spectral observations of asteroid family members provide valuable information regarding parent body interiors, the origin and source regions of near-Earth asteroids, and the link between meteorites and their parent bodies. Asteroids of the Hungaria family represent some of the closest samples to the Earth from a collisional family (∼1.94 AU), permitting observations of smaller family fragments than accessible for Main Belt families. We have carried out a ground-based observational campaign entitled Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS) to record reflectance spectra of these preserved samples from the inner-most regions of the primordial asteroid belt. During HARTSS phase one (Lucas et al. (2017). Icarus 291, 268–287) we found that ∼80% of the background population is comprised of stony S-complex asteroids that exhibit considerable spectral and mineralogical diversity. In HARTSS phase two, we turn our attention to family members to determine if the Hungaria collisional family is compositionally homogeneous or heterogeneous. We use taxonomic classification, geometric albedo (pv) estimates, and near-infrared (NIR) spectral properties to infer the composition of the family. During phase two of HARTSS we acquired NIR spectra of 50 new Hungarias (19 family; 31 background) with the SpeX spectrograph at NASA's Infrared Telescope Facility (IRTF) and with the NICS spectrograph at the Telescopio Nazionale Galileo (TNG). We analyzed X-type spectra for NIR color indices (0.85-J; J-K), and a subtle ∼0.9 µm absorption feature that may be attributed to Fe-poor orthopyroxene ± the sulfide mineral oldhamite. Surviving fragments of an asteroid collisional family typically exhibit similar taxonomies, albedos, and spectral properties. Spectral analysis of Hungaria family X-types and independently calculated WISE albedos for family members (average pv= 0.403; n = 192) is consistent with this scenario. Furthermore, about one-fourth of the background population exhibit similar spectral properties and albedos to family X-types. Spectral observations of 92 Hungaria region asteroids acquired during both phases of HARTSS uncover a compositionally-heterogeneous background population—including two rare olivine-dominated A-types and one apparent D-type interloper—and spectral homogeneity down to ∼2 km for collisional family members. Taxonomy, albedos, and spectral properties indicate that the Hungaria family progenitor was an igneous body that formed under reduced conditions, and was likely consistent in composition with the enstatite achondrite (i.e., aubrite) meteorite group.
... We measured spectral band parameters (Band I and II centers, depths, areas, and BARs) with a new freely-available IDL-based ( Lindsay et al., 2015 ). This routine divides the absorption bands by a straight-line continuum by fitting 5th order polynomials to absorption band shoulders and fitting the linear continuum tangentially to the shoulders. ...
... The final 1 σ center and depth errors are defined as the average of the three error measurements. For a detailed treatment regarding SARA see Lindsay et al. (2015) . The band parameter results for the 24 S-complex Hungaria background asteroids are presented in Table 3 . ...
... 5641 McCleese plots on the L chondrite boundary and we include this object as an L chondrite object, but 1509 Esclangona lies outside of both of the L and LL chondrite regions ( Fig. 5 ). However, in an independent spectral analysis of 1509 Esclangona (from a separate NIR spectral observation), Lindsay et al. (2015) found this asteroid to be an S(IV) subtype with an L chondrite mineralogy. We therefore include 1509 Esclangona in our tally of L chondrite objects. ...
... An incorrect BAR measurement can potentially compromise any of these identifications. We refer to this problem as the "Red Edge Problem," which is briefly explored in Lindsay et al. (2015), Moskovitz et al. (2010), and Duffard et al. (2006). ...
... The band parameter analysis is performed using the IDL-based Spectral Analysis Routine for Asteroids (SARA) code (Lindsay et al. 2015). For the OC RELAB sample, SARA measures band centers using the average of 3rd-, 4th-, and 5th-order polynomial fits to the bottom half of band I and the entirety of band II. ...
... As many of the RELAB spectra do not include error estimates, band parameter uncertainties are not evaluated. For details on how SARA performs its band parameter calculations, see Lindsay et al. (2015). The SARA code is freely available upon request to author Sean S. Lindsay, and it is also publicly available online at https://github.com/SeanSLindsay/SARA.git. ...
Near-infrared reflectance spectra of S-type asteroids contain two absorptions at 1 and 2 μm (band I and II) that are diagnostic of mineralogy. A parameterization of these two bands is frequently employed to determine the mineralogy of S(IV) asteroids through the use of ordinary chondrite calibration equations that link the mineralogy to band parameters. The most widely used calibration study uses a Band II terminal wavelength point (red edge) at 2.50 μm. However, due to the limitations of the NIR detectors on prominent telescopes used in asteroid research, spectral data for asteroids are typically only reliable out to 2.45 μm. We refer to this discrepancy as “The Red Edge Problem.” In this report, we evaluate the associated errors for measured band area ratios (BAR = Area BII/BI) and calculated relative abundance measurements. We find that the Red Edge Problem is often not the dominant source of error for the observationally limited red edge set at 2.45 μm, but it frequently is for a red edge set at 2.40 μm. The error, however, is one sided and therefore systematic. As such, we provide equations to adjust measured BARs to values with a different red edge definition. We also provide new ol/(ol+px) calibration equations for red edges set at 2.40 and 2.45 μm.
... The colored points are binned by 15 pixels, and the gray error bars are presented at the native resolution of the data. used a modified version of the SARA band analysis routine originally developed for asteroid spectra (Lindsay et al. 2015). The band analysis code generates a sample spectrum, drawing from a Gaussian distribution where the mean and standard deviation are the flux and errors of the input spectrum, respectively. ...
... This process is demonstrated visually using a GNIRS spectrum of Miranda's leading hemisphere in Figure 3. To calculate the uncertainties on each measurement, this entire sample spectrum generation and measurement process is repeated 20,000 times, which is a number of samples consistent with other Monte Carlo-type approaches to measurements of band parameters (e.g., Cartwright et al. 2015;Lindsay et al. 2015). The mean and standard deviation of the measurements of this ensemble are reported as the final band measurements for each individual spectrum in Table 3. ...
Published near-IR spectra of the four largest classical Uranian satellites display the presence of discrete deposits of CO 2 ice, along with subtle absorption features around 2.2 μ m. The two innermost satellites, Miranda and Ariel, also possess surfaces heavily modified by past endogenic activity. Previous observations of the smallest satellite, Miranda, have not detected the presence of CO 2 ice, and a report of an absorption feature at 2.2 μ m has not been confirmed. An absorption feature at 2.2 μ m could result from exposed or emplaced NH 3 - or NH 4 -bearing species, which have a limited lifetime on Miranda’s surface, and therefore may imply that Miranda’s internal activity was relatively recent. In this work, we analyzed near-IR spectra of Miranda to determine whether CO 2 ice and the 2.2 μ m feature are present. We measured the band area and depth of the CO 2 ice triplet (1.966, 2.012, and 2.070 μ m), a weak 2.13 μ m band attributed to CO 2 ice mixed with H 2 O ice, and the 2.2 μ m band. We confirmed a prior detection of a 2.2 μ m band on Miranda, but we found no evidence for CO 2 ice, either as discrete deposits or mixed with H 2 O ice. We compared a high signal-to-noise-ratio spectrum of Miranda to synthetic and laboratory spectra of various candidate compounds to shed light on what species may be responsible for the 2.2 μ m band. We conclude that the 2.2 μ m absorption is best matched by a combination of NH 3 ice with NH 3 hydrates or NH 3 –H 2 O mixtures. NH 4 -bearing salts like NH 4 Cl are also promising candidates that warrant further investigation.
... Our band area and depth measurements were conducted with the same analysis routine described in DeColibus et al. (2022), modified for use on the CO 2 ice bands, 2.13-µm band, and 2.2-µm band. This routine is a Python implementation of the technique described in Cartwright et al. (2015Cartwright et al. ( , 2018, which used a modified version of the SARA band analysis routine originally developed for asteroid spectra (Lindsay et al. 2015). The band analysis code generates a sample spectrum, drawing from a Gaussian distribution where the mean and standard deviation are the flux and errors of the input spectrum, respectively. ...
... To calculate the uncertainties on each measurement, this entire sample spectrum generation and measurement process is repeated 20,000 times, which is a number of samples consistent with other Monte Carlo type approaches to measurements of band parameters (e.g. Lindsay et al. 2015;Cartwright et al. 2015). The mean and standard deviation of the measurements of this ensemble are reported as the final band measurements for each individual spectrum in Table 3. ...
Published near-infrared spectra of the four largest classical Uranian satellites display the presence of discrete deposits of CO$_2$ ice, along with subtle absorption features around 2.2 $\mu$m. The two innermost satellites, Miranda and Ariel, also possess surfaces heavily modified by past endogenic activity. Previous observations of the smallest satellite, Miranda, have not detected the presence of CO$_2$ ice, and a report of an absorption feature at 2.2 $\mu$m has not been confirmed. An absorption feature at 2.2 $\mu$m could result from exposed or emplaced NH$_3$- or NH$_4$-bearing species, which have a limited lifetime on Miranda's surface, and therefore may imply that Miranda's internal activity was relatively recent. In this work, we analyzed near-infrared spectra of Miranda to determine whether CO$_2$ ice and the 2.2-$\mu$m feature are present. We measured the band area and depth of the CO$_2$ ice triplet (1.966, 2.012, and 2.070 $\mu$m), a weak 2.13-$\mu$m band attributed to CO$_2$ ice mixed with H$_2$O ice, and the 2.2-$\mu$m band. We confirmed a prior detection of a 2.2-$\mu$m band on Miranda, but we found no evidence for CO$_2$ ice, either as discrete deposits or mixed with H$_2$O ice. We compared a high signal-to-noise spectrum of Miranda to synthetic and laboratory spectra of various candidate compounds to shed light on what species may be responsible for the 2.2-$\mu$m band. We conclude that the 2.2-$\mu$m absorption is best matched by a combination of NH$_3$ ice with NH$_3$-hydrates or NH$_3$-H$_2$O mixtures. NH$_4$-bearing salts like NH$_4$Cl are also promising candidates that warrant further investigation.
... We measured the band parameters of the strong 1 and 2 lm absorption bands (Band I and II, respectively) for eight meteorite spectra from our sample suite, and also the meteorites Acapulco and Lodran. We used an Interactive Data Language (IDL)based code, the Spectral Analysis Routine for Asteroids or SARA (Lindsay et al. 2015) to measure Band I and II centers, depths, areas, band area ratios, and their uncertainties. The band area ratio (BAR) is defined as the ratio of (Band II area)/(Band I area). ...
... The final 1r center and depth errors are defined as the average of the three error measurements. For a detailed description of SARA, see Lindsay et al. (2015). Band parameter results for untreated acapulcoite-lodranite meteorites are presented in Table 7 and band results for EATG treated meteorites are listed in Table 8. ...
Except for asteroid sample return missions, measurements of the spectral properties of both meteorites and asteroids offer the best possibility of linking meteorite groups with their parent asteroid(s). Visible plus near‐infrared spectra reveal distinguishing absorption features controlled mainly by the Fe²⁺ contents and modal abundances of olivine and pyroxene. Meteorite samples provide relationships between spectra and mineralogy. These relationships are useful for estimating the olivine and pyroxene mineralogy of stony (S‐type) asteroid surfaces. Using a suite of 10 samples of the acapulcoite–lodranite clan (ALC), we have developed new correlations between spectral parameters and mafic mineral compositions for partially melted asteroids. A well‐defined relationship exists between Band II center and ferrosilite (Fs) content of orthopyroxene. Furthermore, because Fs in orthopyroxene and fayalite (Fa) content in olivine are well correlated in these meteorites, the derived Fs content can be used to estimate Fa of the coexisting olivine. We derive new equations for determining the mafic silicate compositions of partially melted S‐type asteroid parent bodies. Stony meteorite spectra have previously been used to delineate meteorite analog spectral zones in Band I versus band area ratio (BAR) parameter space for the establishment of asteroid–meteorite connections with S‐type asteroids. However, the spectral parameters of the partially melted ALC overlap with those of ordinary (H) chondrites in this parameter space. We find that Band I versus Band II center parameter space reveals a clear distinction between the ALC and the H chondrites. This work allows the distinction of S‐type asteroids as nebular (ordinary chondrites) or geologically processed (primitive achondrites).
... Following Cartwright et al. (2015), we measured the areas and depths of the 1.52- µm and 2.02-µm bands using a modified version of the Spectral Analysis Routine for Asteroids program (SARA, Lindsay et al., 2015). First, we defined the continuum on either side of both bands (Table 5), taking particular care on the short wavelength end of both H2O band complexes to avoid any residual telluric contributions. ...
... This process was iterated 20,000 times. For more details on this technique, see Lindsay et al. (2015). ...
The large and tidally-locked classical moons of Uranus display longitudinal and planetocentric trends in their surface compositions. Spectrally red material has been detected primarily on the leading hemispheres of the outer moons, Titania and Oberon. Furthermore, detected H2O ice bands are stronger on the leading hemispheres of the classical satellites, and the leading/trailing asymmetry in H2O ice band strengths decreases with distance from Uranus. We hypothesize that the observed distribution of red material and trends in H2O ice band strengths results from infalling dust from Uranian irregular satellites. These dust particles migrate inward on slowly decaying orbits, eventually reaching the classical satellite zone, where they collide primarily with the outer moons. The latitudinal distribution of dust swept up by these moons should be fairly even across their southern and northern hemispheres. However, red material has only been detected over the southern hemispheres of these moons (subsolar latitude 81 S). Consequently, to test whether irregular satellite dust impacts drive the observed enhancement in reddening, we have gathered new ground-based data of the now observable northern hemispheres of these moons (sub-observer latitudes, 17 to 35 N). Our results and analyses indicate that longitudinal and planetocentric trends in reddening and H2O ice band strengths are broadly consistent across both southern and northern latitudes of these moons, thereby supporting our hypothesis. Utilizing a suite of numerical best fit models, we investigate the composition of the reddening agent detected on these moons, finding that both complex organics and amorphous pyroxene match the spectral slopes of our data. We also present spectra that span 2.9 to 4.1 microns, a previously unexplored wavelength range in terms of spectroscopy for the Uranian moons.
... Following Cartwright et al. (2015), we measured the areas and depths of the 1.52- µm and 2.02-µm bands using a modified version of the Spectral Analysis Routine for Asteroids program (SARA, Lindsay et al., 2015). First, we defined the continuum on either side of both bands (Table 5), taking particular care on the short wavelength end of both H2O band complexes to avoid any residual telluric contributions. ...
... This process was iterated 20,000 times. For more details on this technique, see Lindsay et al. (2015). ...
The large and tidally-locked "classical" moons of Uranus display longitudinal and planetocentric trends in their surface compositions. Spectrally red material has been detected primarily on the leading hemispheres of the outer moons, Titania and Oberon. Furthermore, detected H2O ice bands are stronger on the leading hemispheres of the classical satellites, and the leading/trailing asymmetry in H2O ice band strengths decreases with distance from Uranus. We hypothesize that the observed distribution of red material and trends in H2O ice band strengths results from infalling dust from Uranus' irregular satellites. These dust particles migrate inward on slowly decaying orbits, eventually reaching the classical satellite zone, where they collide primarily with the outer moons. The latitudinal distribution of dust swept up by these moons should be fairly even across their southern and northern hemispheres. However, red material has only been detected over the southern hemispheres of these moons, during the Voyager 2 flyby of the Uranian system (subsolar latitude ~81ºS). Consequently, to test whether irregular satellite dust impacts drive the observed enhancement in reddening, we have gathered new ground-based data of the now observable northern hemispheres of these moons (sub-observer latitudes ~17-35ºN). Our results and analyses indicate that longitudinal and planetocentric trends in reddening and H2O ice band strengths are broadly consistent across both southern and northern latitudes of these moons, thereby supporting our hypothesis. Utilizing a suite of numerical best fit models, we investigate the composition of the reddening agent detected on these moons, finding that both complex organics and amorphous pyroxene match the spectral slopes of our data. We also present spectra that span L/L' bands (~2.9-4.1 µm), a previously unexplored wavelength range in terms of spectroscopy for the Uranian moons, and we compare the shape and albedo of the spectral continua in these L/L' band data to other icy moons in the Jovian and Saturnian systems. Additionally, we discuss possible localized enhancement of reddening on Titania, subtle differences in H2O ice band strengths between the southern and northern hemispheres of the classical satellites, the distribution of constituents on Miranda, and the possible presence of NH3-hydrates on these moons. In closing, we explore potential directions for future observational and numerical modeling work in the Uranian system.
... μm spectrum of the Didymos system exhibiting an S-type spectrum through the impact period, accompanied by variation in spectral slope in 2022 October when the ejecta contribution to the flux was significant. These findings are all consistent with the current paradigms of the formation process for binary systems like Didymos (Lindsay et al. 2015;Margot et al. 2015), in which Dimorphos is derived from Didymos itself via rotational fission (Pajola et al. 2022). Consequently, measurements of Didymos provide our best current insight into the composition of Dimorphos, until the arrival of the ESA Hera mission. ...
The Didymos binary asteroid was the target of the Double Asteroid Redirection Test (DART) mission, which intentionally impacted Dimorphos, the smaller member of the binary system. We used the Near-Infrared Spectrograph and Mid-Infrared Instrument instruments on JWST to measure the 0.6–5 and 5–20 μ m spectra of Didymos approximately two months after the DART impact. These observations confirm that Didymos belongs to the S asteroid class and is most consistent with LL chondrite composition, as was previously determined from its 0.6–2.5 μ m reflectance spectrum. Measurements at wavelengths >2.5 μ m show Didymos to have thermal properties typical for an S-complex asteroid of its size and to be lacking absorptions deeper than ∼2% due to OH or H 2 O. Didymos’ mid-infrared emissivity spectrum is within the range of what has been measured on S-complex asteroids observed with the Spitzer Space Telescope and is most consistent with emission from small (<25 μ m) surface particles. We conclude that the observed reflectance and physical properties make the Didymos system a good proxy for the type of ordinary chondrite asteroids that cross near-Earth space, and a good representative of likely future impactors.
... For S-complex and V-type asteroids, the 1 μm and 2 μm absorption bands in the spectra (BI and BII, respectively) were characterized by the band center wavelengths (BIC and BIIC) and the band-area ratio (BAR). This band parameter analysis was conducted on the prism data using the Band Analysis Routine for Asteroids (BAR-Ast; MacLennan 2019), an algorithm based on the Spectral Analysis Routine for Asteroids (SARA; Lindsay et al. 2015). SARA uses fifth-order polynomials to define the wavelength minima and maxima of BI and BII, after which it fits third-, fourth-, and fifth-order polynomials to BI and BII to find the band centers and other band parameters. ...
Near-Earth Asteroids (NEAs) are excellent laboratories for processes that affect airless body surfaces. S-complex (including V-type) NEAs were not expected to contain OH/H 2 O on their surfaces because they formed in the anhydrous regions of the solar system and their surface temperatures are high enough to remove these volatiles. However, a 3 μ m feature typically indicative of OH/H 2 O was identified on other seemingly dry bodies in the inner solar system, raising the question of how widespread volatiles may be on NEAs. We observed 29 NEAs using both prism (0.7–2.52 μ m) and LXD_short (1.67–4.2 μ m) modes on SpeX on NASA’s IRTF in order to accurately characterize asteroid spectral type and the 3 μ m region. Eight of the observed NEAs have a 3 μ m absorption feature at >1 σ (three of which are present to >2 σ ), and they exhibit four identified band shape types. Possible sources for OH/H 2 O on these bodies include carbonaceous chondrite impacts and/or interactions with protons implanted by solar wind. Characteristics such as composition and aphelion appear to play an important role in the delivery and/or retention of OH/H 2 O, as all eight NEAs with an absorption feature are S-complex asteroids and six enter the main asteroid belt. Additionally, perihelion, size, albedo, and orbital period may play a minor role. Our observations determined that nominally anhydrous, inner solar system bodies, and therefore near-Earth space in general, contain more OH/H 2 O than previously expected. The identified trends should help predict which NEAs that have not yet been observed might contain OH/H 2 O on their surfaces.
... Our band area and depth measurements were conducted with a Python implementation of the technique described in Cartwright et al. (2015Cartwright et al. ( , 2018, which used a modified version of the SARA band analysis routine originally developed for asteroid spectra (Lindsay et al. 2015). All of our analyses used unbinned, native resolution spectra. ...
Many tidally locked icy satellites in the outer solar system show leading/trailing hemispherical asymmetries in the strength of near-infrared (NIR) H 2 O ice absorption bands, in which the absorption bands are stronger on the leading hemisphere. This is often attributed to a combination of magnetospheric irradiation effects and impact gardening, which can modify grain size, expose fresh ice, and produce dark contaminating compounds that reduce the strength of absorption features. Previous research identified this leading/trailing asymmetry on the four largest classical Uranian satellites but did not find a clear leading/trailing asymmetry on Miranda, the smallest and innermost classical moon. We undertook an extensive observational campaign to investigate variations of the NIR spectral signature of H 2 O ice with longitude on Miranda’s northern hemisphere. We acquired 22 new spectra with the TripleSpec spectrograph on the ARC 3.5 m telescope and four new spectra with GNIRS on Gemini North. Our analysis also includes three unpublished and seven previously published spectra taken with SpeX on the 3 m IRTF. We confirm that Miranda has no substantial leading/trailing hemispherical asymmetry in the strength of its H 2 O ice absorption features. We additionally find evidence for an anti-Uranus/sub-Uranus asymmetry in the strength of the 1.5 μ m H 2 O ice band that is not seen on the other Uranian satellites, suggesting that additional endogenic or exogenic processes influence the longitudinal distribution of H 2 O ice band strengths on Miranda.
... Our band area and depth measurements were conducted with a Python implementation of the technique described in Cartwright et al. (2015Cartwright et al. ( , 2018, which used a modified version of the SARA band analysis routine originally developed for asteroid spectra (Lindsay et al. 2015). All of our analyses used unbinned, native resolution spectra. ...
Many tidally locked icy satellites in the outer Solar System show leading/trailing hemispherical asymmetries in the strength of near-infrared (NIR) H$_2$O ice absorption bands, in which the absorption bands are stronger on the leading hemisphere. This is often attributed to a combination of magnetospheric irradiation effects and impact gardening, which can modify grain size, expose fresh ice, and produce dark contaminating compounds that reduce the strength of absorption features. Previous research identified this leading/trailing asymmetry on the four largest classical Uranian satellites but did not find a clear leading/trailing asymmetry on Miranda, the smallest and innermost classical moon. We undertook an extensive observational campaign to investigate variations of the NIR spectral signature of H$_2$O ice with longitude on Miranda's northern hemisphere. We acquired 22 new spectra with the TripleSpec spectrograph on the ARC 3.5m telescope and 4 new spectra with GNIRS on Gemini North. Our analysis also includes 3 unpublished and 7 previously published spectra taken with SpeX on the 3m IRTF. We confirm that Miranda has no substantial leading/trailing hemispherical asymmetry in the strength of its H$_2$O ice absorption features. We additionally find evidence for an anti-Uranus/sub-Uranus asymmetry in the strength of the 1.5-$\mu$m H$_2$O ice band that is not seen on the other Uranian satellites, suggesting that additional endogenic or exogenic processes influence the longitudinal distribution of H$_2$O ice band strengths on Miranda.
... According to Cloutis et al. (1986), the BAR is a nearly linear function of Ol to Opx abundance and is insensitive to grain size. The relationship between the BAR and the Band I center is widely used in mineralogical investigations of the Moon and asteroids (e.g., Gaffey et al., 1993;Lindsay et al., 2015Lindsay et al., , 2016Zhang et al., 2016Zhang et al., , 2019. Zhang and Cloutis (2020) investigated a variety of lunar ferrous samples and determined the lunar Ol-Cpx (clinopyroxene, i.e., high-calcium pyroxene)-Opx mixing line for rocks and minerals in the plot of the BAR versus the Band I center (Figure 1). ...
In near‐infrared spectral studies, the relationship between the 1‐μm absorption (Band I) center and the band area ratio (BAR, the area ratio of 2–1‐μm absorption features) is useful in compositional and mineralogical analyses of ferrous mineral‐bearing mixtures. Zhang and Cloutis (2020), https://doi.org/10.1029/2020ea001153, investigated various lunar ferrous iron‐bearing rocks and minerals and found that pyroxene‐bearing materials rich in ilmenite (Ilm), plagioclase (Pl), or glass are offset from the lunar olivine‐clinopyroxene‐orthopyroxene (Ol‐Cpx‐Opx) mixing line in the plot of the BAR versus the Band I center. To analyze the variation trends of the spectral properties of these mixtures with different components, this study presents a systematic evaluation of laboratory spectra of terrestrial and synthetic ferrous iron‐bearing mineral mixtures based on published databases. In general, the mixing trends of the Pl‐pyroxene mixtures, the glass‐pyroxene mixtures, and the Ilm‐basalt mixtures are consistent with the findings of Zhang and Cloutis (2020), https://doi.org/10.1029/2020ea001153. Moreover, this study also finds that the BAR of the Pl‐pyroxene mixtures varies nonlinearly with different relative abundances and that the BAR is generally not sensitive to Pl abundances below 60%. For glass‐pyroxene mixtures, the corresponding data points are usually appreciably offset from the Ol‐Cpx‐Opx mixing line at glass abundances above 20%. The BAR of the Ilm‐basalt mixtures increases with increasing Ilm content, mainly due to the weakening of 1‐μm absorption generally being greater than that of 2‐μm absorption.
... According to the original paper by Cloutis et al. (1986), the band area is defined as the area enclosed by the spectral curve and a straight line tangent to the relative maxima that define the band, and so, the band area ratio is computed without continuum removal. Although this initial definition is clear, and has been followed by some authors (Gaffey et al. 1993;Moskovitz et al. 2010), we have also found many examples in the literature where the authors remove the continuum before computing the band areas (Duffard, Lazzaro & de León 2005;Sanchez et al. 2012;Hardersen et al. 2014;Lindsay et al. 2015;Hardersen et al. 2018). Interestingly, we found that the computed BAR values change significantly depending on the way they are computed, i.e. with or without continuum removal. ...
The main objective of this work is to compositionally analyse the visible to near-infrared spectra of a total of six V-type candidates identified using the MOVIS (Y-J) versus (J-Ks) colour–colour plot and located outside the Vesta collisional family. We obtained visible and near-infrared spectra of these asteroids using the 2.54m Isaac Newton Telescope, the 2.5m Nordic Optical Telescope, and the 3.58m Telescopio Nazionale Galileo, all located at the El Roque de Los Muchachos Observatory (La Palma, Spain), as well as the 3.0m NASA Infrared Telescope Facility, located at the Mauna Kea Observatory in Hawaii. We computed several diagnostic spectral parameters (slopes, band centres, band depths, band area ratio, or BAR) and compared them to the ones known for HED meteorites and (4) Vesta. The taxonomic classification confirmed five out of the six candidates as V-types, leading to an identification success rate about 83 per cent. In general, the spectral parameters obtained for the five V-types are in good agreement with those of HED meteorites and (4) Vesta. The exception is asteroid (2452) Lyot, a V-type in the outer belt, located very close to (1459) Magnya, but showing distinct [Wo] and [Fs] molar contents both from Magnya and Vesta, pointing toward a diogenitic compostion. We also studied the dependency of the BAR parameter on the way it is computed (removing or not the continuum), the spectral slope, and the last point used to delimit the right wing of the absorption band at 2 μm.
... 8.7, 8.8 and 8.9), which occupies the same position as the band I centre found in S-type asteroids. In silicate-bearing asteroids, the band I feature corresponds to electronic transitions from vibrating Fe 2+ ions, located in the M1 and M2 crystal lattice sites of pyroxene and, to a lesser extent, olivine (Burns, 1970;Klima et al., 2007;Lindsay et al., 2015). Consequently, the 0.9μm feature found in these C-type asteroids could also represent the excitation of Fe 2+ ions within mafic silicates. ...
Micrometeorites are millimetre-scale cosmic dust grains, derived from asteroids and comets. They represent the largest flux of extraterrestrial material currently falling to Earth, with an estimated contribution of 20,000-60,000 tons per year. In this thesis, the geological history, parent body properties and atmospheric entry of fine-grained micrometeorites are investigated through micro-analysis and spectroscopic techniques.
The degree of aqueous alteration within fine-grained micrometeorites was investigated using criteria initially developed for CM chondrites (Chapt.3). This revealed that most particles are intensely altered, with petrologic subtypes <CM2.3. Textural and geochemical evidence of aqueous alteration is seen in the form of hydrated CAIs, hydrated sulfides, pseudomorphic chondrules and complex intergrown and cross-cut assemblages of phyllosilicate, which attest to extended periods in contact with liquid water. Likewise, the apparent overabundance of CM-like matrix and the relative paucity of C2 chondrule material among fine-grained micrometeorites suggest that the parent bodies of fine-grained micrometeorites are predominantly intensely aqueously altered bodies.
This study also identified the first evidence for shock deformation in fine-grained micrometeorites (Chapt.6). Weak, pervasive petrofabrics, formed by aligned phyllosilicates and inferred from dehydration crack orientations were observed in the majority of micrometeorites studied (21). This requires relatively low peak pressures (<5GPa) and is most likely achieved by successive low-intensity impact events. The presence of a single micrometeorite containing brittle deformation cataclasis fabrics also provides evidence for brittle deformation shock processing of micrometeorites.
The first near-IR spectra of micrometeorites were collected and directly compared against the NIR spectra of young C-type asteroids (Chapt.8). Although these comparisons proved inconclusive, owing to limitations in the quality of the micrometeorite spectra, this study identified the first evidence of hydroxyl-group absorption bands at NIR wavelengths in Veritas family asteroids, suggesting the presence of intact phyllosilicates on their surfaces and thereby adding support to the genetic link between fine-grained micrometeorites and C-type asteroids.
Mid-IR spectroscopy revealed how micrometeorite mineralogy evolves during flash heating in the upper atmosphere, demonstrating that solid state recrystallization preserves pre-atmospheric textures, despite major changes in the mineralogy (Chapt.4). Spatially resolved Raman spectroscopy was used to investigate thermal gradients within micrometeorites during atmospheric entry and revealed that most micrometeorite cores preserve low-temperature (<300°C) carbonaceous phases inherited from their parent asteroid (Chapt.5). The development of secondary interconnected porosity was described for the first time, detailing how the growth and expansion of dehydration cracks driven by the out-gassing of volatiles leads to the formation of branching and sinuous channels (Chapt.7). These channels play an important role in the efficient heating of micrometeorite cores resulting in partial melting as scoriaceous micrometeorites are formed. In addition, the development of secondary porosity significantly lowers the mechanical strength of micrometeoroids, promoting their disruption in the atmosphere.
Finally, a small-scale study, attempting to retrieve fine-grained micrometeorites preserved in ancient sedimentary rocks was trailed (Chapt.9). This led to the recovery of a new collection of fossil micrometeorites derived from Cretaceous chalk. Although no unmelted micrometeorites were discovered, the preserved cosmic spherules are found to have experienced complete diagenetic alteration, resulting in preserved micro-textures and replaced terrestrial mineralogies. A repeat study at a different time period and location also found cosmic spherules with identical preservation styles, suggesting that diagenetically altered micrometeorites most likely represent the most common form of cosmic dust on Earth.
... Band depths are not diagnostic of mineralogy and can vary based on the asteroid's phase angle during observations, space weathering on an asteroid's surface, or a surface metal component (Britt & Pieters 1988;Blewett et al. 2015;Cloutis et al. 1990Cloutis et al. , 2015Sanchez et al. 2014). Our analysis of band parameters utilizes a set of MATLAB routines (Reddy et al. 2012a) and the IDL-based Spectral Analysis Routine for Asteroids (SARA) (Lindsay et al. 2015). While both sets of code extract the same band parameters, the MATLAB method is semi-automated and the SARA method is completely automated. ...
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 μm) 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 μm. 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. © 2018. The American Astronomical Society. All rights reserved.
... Later on, both Bus and Binzel (2002a) and Lazzaro et al. (2004) classified it as X, based on visible spectra. More recently, based on a nearinfrared spectrum from NASA IRTF Spex, Lindsay et al. (2015) classified Camilla as either Xe or L. ...
The population of large asteroids is thought to be primordial and they are the most direct witnesses of the early history of our Solar System. Those satellites allow study of the mass, and hence density and internal structure. We study here the properties of the triple asteroid (107) Camilla from lightcurves, stellar occultations, optical spectroscopy, and high-contrast and high-angular-resolution images and spectro-images. Using 80 positions over 15 years, we determine the orbit of its larger satellite to be circular, equatorial, and prograde, with RMS residuals of 7.8 mas. From 11 positions in three epochs only, in 2015 and 2016, we determine a preliminary orbit for the second satellite. We find the orbit to be somewhat eccentric and slightly inclined to the primary's equatorial plane, reminiscent of the inner satellites of other asteroid triple systems. Comparison of the near-infrared spectrum of the larger satellite reveals no significant difference with Camilla. Hence, these properties argue for a formation of the satellites by excavation from impact and re-accumulation of ejecta. We determine the spin and 3-D shape of Camilla. The model fits well each data set. We determine Camilla to be larger than reported from modeling of mid-infrared photometry, with a spherical-volume-equivalent diameter of 254 $\pm$ 36 km (3 $\sigma$ uncertainty), in agreement with recent results from shape modeling (Hanus2017+). Combining the mass of (1.12 $\pm$ 0.01) $\times$ 10$^{19}$ kg determined from the dynamics of the satellites and the volume from the 3-D shape model, we determine a density of 1,280 $\pm$ 130 SI. From this density, and considering Camilla's spectral similarities with (24) Themis and (65) Cybele (for which water ice coating on surface grains was reported), we infer a silicate-to-ice mass ratio of 1-6, with a 10-30% macroporosity.
... Where is sometimes called the "bolometric emissivity" (Emery et al., , 2006Hanuš et al., 2015;Lagoa et al., 2011;Lim et al., 2011;Lindsay et al., 2014;Marchis et al., 2012;Mueller, 2012). ...
This study addresses thermal modeling of asteroids with a new derivation of the Near Earth Asteroid Thermal (NEATM) model which correctly accounts for the presence of reflected sunlight in short wave IR bands. Kirchhoff's law of thermal radiation applies to this case and has important implications. New insight is provided into the eta parameter in the NEATM model and it is extended to thermal models besides NEATM. The role of surface material properties on eta is examined using laboratory spectra of meteorites and other asteroid compositional proxies; the common assumption that emissivity e=0.9 in asteroid thermal models may not be justified and can lead to misestimating physical parameters. In addition, indeterminacy in thermal modeling can limit its ability to uniquely determine temperature and other physical properties. A new curve fitting approach allows thermal modeling to be done independent of visible band observational parameters such as the absolute magnitude H. These new thermal modeling techniques are applied to observational data for selected asteroids from the WISE/NEOWISE mission. The previous NEOWISE analysis assumes Kirchhoff's law does not apply. It also deviates strongly from established statistical practice and systematically underestimates the sampling error inherent in observing potentially irregular asteroids from a finite sample of observations. As a result, the new analysis finds asteroid diameter and other physical properties that have large differences from published NEOWISE results, with greatly increased error estimates. NEOWISE results have a claimed +/-10% accuracy for diameter estimates, but this is unsupported by any calculations and undermined by irregularities in the NEOWISE results. ABSTRACT CONTINUED IN PDF...
... In order to rule out possible problems with our code we used two additional programs to measure the band parameters, the Spectral Analysis Routine for Asteroids (SARA), developed by Lindsay et al. (2015), which is an IDL-based band parameter analysis routine, and the Modeling for Asteroid Spectra (M4AST) package developed by Popescu et al. (2012). This is an online tool 3 used for modeling visible and NIR spectra of asteroids, and it is the same tool used by Nedelcu et al. (2014). ...
Potentially hazardous asteroids (PHAs) represent a unique opportunity for physical characterization during their close approaches to Earth. The proximity of these asteroids makes them accessible for sample-return and manned missions, but could also represent a risk for life on Earth in the event of collision. Therefore, a detailed mineralogical analysis is a key component in planning future exploration missions and developing appropriate mitigation strategies. In this study we present near-infrared spectra (∼0.7–2.55 μm) of PHA (214869) 2007 PA8 obtained with the NASA Infrared Telescope Facility during its close approach to Earth on 2012 November. The mineralogical analysis of this asteroid revealed a surface composition consistent with H ordinary chondrites. In particular, we found that the olivine and pyroxene chemistries of 2007 PA8 are Fa 18 (Fo 82) and Fs 16 , respectively. The olivine–pyroxene abundance ratio was estimated to be 47%. This low olivine abundance and the measured band parameters, close to the H4 and H5 chondrites, suggest that the parent body of 2007 PA8 experienced thermal metamorphism before being catastrophically disrupted. Based on the compositional affinity, proximity to the J5:2 resonance, and estimated flux of resonant objects we determined that the Koronis family is the most likely source region for 2007 PA8.
... Some overlapping is expected between the two fields, however, as they are defined by a similar mineralogy (Gaffey et al., 1993). These variations caused by geometry effects might add to the variations due to different BAR calculation methods (i.e., choice of different wavelengths for the tie points) as demonstrated in Lindsay et al. (2015). Thus, caution should be paid when comparing BAR values calculated with different methods and from different observations. ...
... For spectra with visibly apparent CO2 bands, we fit their band centers using Gaussian curves in order to estimate deviations between the position of the detected CO2 bands and pure CO2 ice (e.g., Gerakines et al., 2005). Band parameter analyses were conducted using a modified version of the Spectral Analysis Routine for Asteroids program (SARA, Lindsay et al., 2015), which we repurposed for the analysis of CO2 and H2O ice bands. Each of these steps is described in greater detailed in sub-sections 4.1.1 ...
The surfaces of the large uranian satellites are characterized by a mixture of H2O ice and a dark, potentially carbon-rich, constituent, along with CO2 ice. At the mean heliocentric distance of the uranian system, native CO2 ice should be removed on timescales shorter than the age of the Solar System. Consequently, the detected CO2 ice might be actively produced. Analogous to irradiation of icy moons in the Jupiter and Saturn systems, we hypothesize that charged particles caught in Uranus’ magnetic field bombard the surfaces of the uranian satellites, driving a radiolytic CO2 production cycle. To test this hypothesis, we investigated the distribution of CO2 ice by analyzing near-infrared (NIR) spectra of these moons, gathered using the SpeX spectrograph at NASA’s Infrared Telescope Facility (IRTF) (2000–2013). Additionally, we made spectrophotometric measurements using images gathered by the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (2003–2005). We find that the detected CO2 ice is primarily on the trailing hemispheres of the satellites closest to Uranus, consistent with other observations of these moons. Our band parameter analysis indicates that the detected CO2 ice is pure and segregated from other constituents. Our spectrophotometric analysis indicates that IRAC is not sensitive to the CO2 ice detected by SpeX, potentially because CO2 is retained beneath a thin surface layer dominated by H2O ice that is opaque to photons over IRAC wavelengths. Thus, our combined SpeX and IRAC analyses suggest that the near-surfaces (i.e., top few 100 μm) of the uranian satellites are compositionally stratified. We briefly compare the spectral characteristics of the CO2 ice detected on the uranian moons to icy satellites elsewhere, and we also consider the most likely drivers of the observed distribution of CO2 ice.
... A second series of spectral band measurements was calculated using the 'Spectral Analysis Routine for Asteroids', or SARA, which is a collection of IDL routines that automatically calculate absorption band centers, band areas, BARs, band slope, and band depths from an input text file of an average normalized asteroid reflectance spectrum (Lindsay et al., 2013(Lindsay et al., , 2014. As compared to the MATLAB routines where the spectral band parameters are obtained semi-automatically one set at a time, SARA inputs a spectrum and calculates all of the spectral band parameters simultaneously. ...
This work reports high quality NIR spectra, and their respective
interpretations, for eight Vp type asteroids, as defined by Carvano et al.
(2010), 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 micron
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 et al., 2012; Lindsay et al.,
2013,2014; Gaffey et al., 2002; Burbine et al., 2009). (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 exposure to irradiation from high‐energy particles alters the reflectance properties of asteroid surfaces and is referred to as space weathering . This process leads to an increase in spectral slope in visible and near‐infrared wavelengths. However, changes in the regolith particle size, which can vary dramatically among the asteroid population, are known to influence the spectral properties of meteorites and asteroids. In this context, we investigate the changes in spectral slope and absorption band depths of fresh and irradiated ordinary chondrite meteorites to quantitatively compare the effects of space weathering and grain size variations. To do so, we develop and employ the Spectral Analysis for Asteroid Reflectance Investigation routine that calculates the band parameters of reflectance spectra. We then formulate a parameter called the Space Weathering Index ( SWI ) that is designed to encapsulate spectral changes due to space weathering. We find that the SWI is strongly dependent on the spectral slope which complicates the interpretation of asteroid spectra in the context of grain size variations and space weathering. We also show that a second parameter, the Band Depth Index, is indicative of petrologic type. Finally, we use a linear discriminant analysis to classify asteroid reflectance spectra into H, L, LL, and unequilibrated ordinary chondrites.
Context . Recently, a primordial family of moderate-albedo asteroid fragments was discovered in the inner main belt. Its age was estimated to be 4.4 ± 1.7 Gyr. However, there is a lack of compositional characterization, which is important to the study of the earliest collisions in the main belt.
Aims . In addition to the previously identified members and the parameters that define the family’s borders (V shape), we expanded the list of family members to include asteroids located within the central region of the V shape. These additional potential members were selected based on their diameter (larger than 7 km) and their geometric visible albedo (greater than or equal to 12%). Subsequently, we conducted a spectroscopic survey to determine the dominant taxonomy and composition of this family. This allowed us to further refine the list of family members by removing interlopers.
Methods . From an initial list of 263 asteroids that are considered to be potential members of the aforementioned primordial family, we retrieved their spectra in the visible and near-infrared range from the literature and from the Gala DR3 spectral catalog of Solar System objects. For asteroids with no or poor signal-to-noise ratio spectra in the literature, we carried out new ground-based observations. We obtained new spectra for 33 members of the family using the 1.82 m Asiago Telescope for the visible spectroscopy, while for near-infrared spectroscopy, we used the 3.58 m Telescopio Nazionale Galileo (TNG) and the 4.30 m Lowell Discovery Telescope (LDT).
Results . In total, we collected spectra for 261 potential members of the primordial S-type family out of 263. We determined their spectral taxonomy and properties, such as spectral slopes and absorption band parameters, when existing. Using the taxonomical characterization and the orbital space parameters, we identified and removed 71 interlopers from the potential members list. The final list of the primordial S-type family members includes 190 asteroids. The family is dominated by S-complex (~71%) asteroids with a mineralogy similar to ordinary chondrites and pyroxene-rich minerals. The family also contains members classified as L-types and V-types. (~15% and ~9%, respectively).
Conclusions . The mean albedo of the family is ~23%, and its largest probable remnant is the asteroid (30) Urania. The estimated size of the family parent body ranges between 110 and 210 km. This size range is compatible with the progenitor of H and L chondrites.
Low-albedo asteroids preserve a record of the primordial solar system planetesimals and the conditions in which the solar nebula was active. However, the origin and evolution of these asteroids are not well-constrained. Here we measured visible and near-infrared (0.5 - 4.0 microns) spectra of low-albedo asteroids in the mid-outer main belt. We show that numerous large (d > 100 km) and dark (geometric albedo < 0.09) asteroids exterior to the dwarf planet Ceres' orbit share the same spectral features, and presumably compositions, as Ceres. We also developed a thermal evolution model that demonstrates that these Ceres-like asteroids have highly-porous interiors, accreted relatively late at 1.5 - 3.5 Myr after the formation of calcium-aluminum-rich inclusions, and experienced maximum interior temperatures of < 900 K. Ceres-like asteroids are localized in a confined heliocentric region between 3.0 - 3.4 au but were likely implanted from more distant regions of the solar system during the giant planet's dynamical instability.
Context. Andesitic meteorites are among the oldest achondrites known to date. They record volcanic events and crust formation episodes in primordial planetesimals that took place about 4.565 Myr ago. However, no analogue for these meteorites has been found in the asteroid population to date.
Aims. We searched for spectroscopic analogues of the andesitic meteorite Erg Chech 002 in the asteroid population using the Gaia DR3 spectral dataset.
Methods. In order to identify which asteroids have the most similar spectrum to Erg Chech 002, we first determined the spectral parameters of Gaia DR3 asteroids (spectral slope and Band I depth) and compared them to the spectral parameters of different samples of the meteorite. In addition, we performed a spectral curve matching between Erg Chech 002 and Gaia DR3 asteroid data, and we compared the results of both methods.
Results. We found that 51 main-belt asteroids have a visible spectrum similar to the one of Erg Chech 002, and 91 have a spectrum similar to the space-weathered spectra of the meteorite, corresponding to 0.08% and 0.15% of the whole Gaia DR3 dataset of asteroids with spectra, respectively. The asteroids that best match the laboratory samples of the meteorite are mostly located in the inner main belt, while the objects matching the space-weathered meteorite models show slightly more scattering across the belt.
Conclusions. Despite the fact that we find asteroids that potentially match Erg Chech 002, these asteroids are extremely rare. Moreover, a visible spectrum alone is not completely diagnostic of an Erg Chech 002-like composition. Near-infrared spectra will be important to confirm (or rule out) the spectral matches between Erg Chech 002 and the candidate asteroid population.
The visible and near-infrared spectra (0.5–2.5 μm) of ordinary chondrite (OC) meteorites are characterized by absorptions at 1 and 2 μm, typically denoted as Band I and Band II, respectively. Previous works have connected parameterization of Band I and Band II, a so-called band parameter analysis (BPA) of mineralogical abundances and chemistry of OC meteorites. In particular, parameters for these determinations include the center of the Band I feature (BIC) and band area ratio (BAR), the ratio of Band II's area to that of Band I. Through treating BIC as a function of BAR, OCs plot within a region called the “OC-boot,” first shown in Gaffey et al. (1993). The boundaries for the OC-Boot have remained unchanged since their foundational work, and numerous investigations using various different methods have employed the same boundaries for the OC-Boot's original zoning. By applying the Spectral Analysis Routine for Asteroids (SARA) to >150 spectra of OCs from Brown University's NASA/Keck Reflectance Experiment Laboratory (RELAB) database, we highlight the issue of the OC-Boot's dependency on BPAs. Namely, we vary how Band I and Band II are defined to highlight the BPA-dependency by producing band edge-specific OC-Boots that encompass the mineralogical diversity of OCs (H, L, and LL subtypes) with corresponding spectral ranges. We conclude that there is no single canonical OC-boot and suggest that researchers create their own OC-Boot using their specific BPA or select an OC-boot in the literature that most closely matches their methods of determining band parameters.
The ordinary chondrite boot (OC-Boot) is a diagnostic region generated from spectral analyses of the features caused by electron absorptions in the olivine and orthopyroxene of OCs. In our companion article to this one, McClure & Lindsay (2022a) demonstrated that the boundaries of the OC-Boot are band parameter analysis (BPA) dependent. Here, we highlight how using OC-Boot boundaries that are not derived from a self-consistent BPA analysis can lead to potential misidentification of ordinary chondrite-like asteroid analogs. We compare S-type asteroid spectral band parameters to the OC-Boot defined in McClure & Lindsay (2022a) and the OC-Boot defined in Gaffey et al. (1993). We choose the Gaffey et al. (1993) OC-Boot for this comparison since its use is frequently seen in the literature without updated boundaries. By applying the Spectral Analysis Routine for Asteroids (SARA) to spectra from the MIT-Hawaii Near-Earth Object Spectroscopic (MITHNEOS) Survey, we demonstrate an overlap between the contemporary view of the OC-Boot and OC analogs, showing that a self-consistent OC-Boot framework captures the variation of the Near-Earth asteroids (NEAs) more than the original OC-Boot. In particular, we show the OC-Boots from McClure & Lindsay (2022a) encompass relatively more NEAs. We also apply a set of calibration equations derived using SARA to determine the mineral abundances and compositions for the S-type asteroids. We find that 59.57% of NEAs exhibit LL-like mineralogies and that H-like and L-like mineralogies are exhibited 19.15% and 6.38% of cases, respectively. There are a couple of cases wherein the mineralogies could be in between subtypes and five cases where no subtype designation could be determined. The high-frequency of LL-like mineralogies is in agreement with previous studies on S-type NEAs.
Olivine and pyroxene are important mineral end-members for studying the surface material compositions of mafic bodies. The profiles of visible and near-infrared spectra of olivine-orthopyroxene mixtures systematically varied with their composition ratios. In our experiments, we combine the RELAB spectral database with a new spectral data obtained from some assembled olivine-orthopyroxene mixtures. We found that the commonly-used band area ratio (BAR, Cloutis et al. 1986) does not work well on our newly obtained spectral data. To investigate this issue, an empirical procedure based on fitted results by modified Gaussian model is proposed to analyze the spectral curves. Following the new empirical procedure, the end-member abundances can be estimated with a 15% accuracy with some prior mineral absorption features. In addition, the mixture samples configured in our experiments are also irradiated by pulsed lasers to simulate and investigate the space weathering effects. Spectral deconvolution results confirm that low-content olivine on celestial bodies are difficult to measure and estimate. Therefore, the olivine abundance of space weathered materials may be underestimated from remote sensing data. This study may be used to quantify the spectral relationship of olivine orthopyroxene mixtures and further reveal their correlation between the spectra of ordinary chondrites and silicate asteroids.
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.
Binary asteroids represent a natural laboratory to gather crucial information on small bodiesof the Solar System, providing an overview of the formation and evolution mechanisms of these objects. Their physical characterization can constrain the processes that took part in the formation and evolution of planetessimals in the Solar System. The characteristics assessed in this work are: mass, size, shape, spin, density, surface composition, and taxonomy.One of the most important characteristics that can be obtained of binaries -if the system can be resolved- is their mass through their mutual gravitational interaction. From the mass and the size of the asteroid we determine its density, which provides insight on its internal structure.For this purpose, data mining has been done for high-angular resolution images from HST and ground-based telescopes equipped with adaptive optics (VLT/NACO, VLT/SPHERE, Gemini/NIRI, Keck/NIRC2) in the visible and near infrared. Having reduced the images and determined the satellite positions for over many epochs, the genetic algorithm Genoid algorithm is used to determine the orbit of the companion, and mass of the primary. This improves the ephemerides of binary companions, which in turn allows to stellar occultations by asteroids for future occultation campaigns.The occultation technique is the most fruitfulfor observing small diameter Solar System objects. As for the size and shape determination, KOALA multidata inversion algorithm is used.Concerning photometry, light curves and SDSS colors have been obtained for binary asteroids from T1M at Pic du Midi & 1.20m telescope at Haute Provence Observatory, aiming at determining and refining their properties. I remotely acquired spectra of binary asteroids using Spex/IRTF system based on 3m at Mauna Kea (Hawaii), to determine their taxonomic class for the first time. Additionally, I collected spectra of small binaries from the SMASS collaborationdatabase, modelled it, and found their taxonomy. I compare the now larger sample of classified binaries to the population of NEAs and Mars Crossers, and found a predominance of Q/S types. This is in agreement with a formation by YORP spin-up and rotational disruption.Finally, I developed a taxonomic classification for asteroids in general, based on infrared large band photometry, and applied it to 30,000 asteroids from VHS survey at the ESO’s telescope VISTA.
Impacting an asteroid with a spacecraft traveling at high speed delivers an impulsive change in velocity to the body. In certain circumstances, this strategy could be used to deflect a hazardous asteroid, moving its orbital path off of an Earth-impacting course. However, the efficacy of momentum delivery to asteroids by hypervelocity impact is sensitive to both the impact conditions (particularly velocity) and specific characteristics of the target asteroid. Here we numerically model asteroid response to kinetic impactors under a wide range of initial conditions, using an Adaptive Smoothed Particle Hydrodynamics code. Impact velocities spanning 1 to 30 km/s were investigated, yielding, for a particular set of assumptions about the modeled target material, a power-law dependence consistent with a velocity-scaling exponent of μ = 0.44. Target characteristics including equation of state, strength model, porosity, rotational state, and shape were varied, and corresponding changes in asteroid response were documented. The kinetic-impact momentum-multiplication factor, β, decreases with increasing asteroid cohesion and increasing porosity. Although increased porosity lowers β, larger porosities result in greater deflection velocities, as a consequence of reduced target masses for asteroids of fixed size. Porosity also lowers disruption risk for kinetic impacts near the threshold of disruption. Including fast (P = 2.5 hr) and very fast (P = 100 s) rotation did not significantly alter β but did affect the risk of disruption by the impact event. Asteroid shape is found to influence the efficiency of momentum delivery, as local slope conditions can change the orientation of the crater ejecta momentum vector. These results emphasize the need for asteroid characterization studies to bracket the range of target conditions expected at near-Earth asteroids while also highlighting some of the principal uncertainties associated with the kinetic-impact deflection strategy.
Improving 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 greater than 2.5 AU)
that are likely unrelated to (4) Vesta.
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 August
and September 2014 utilizing the SpeX spectrograph at the NASA Infrared
Telescope Facility (IRTF), Mauna Kea, Hawaii. Spectral band parameter (band
centers, Band Area Ratios) and mineralogical analysis (pyroxene chemistry) for
each average asteroid NIR reflectance spectrum suggests a
howardite-eucrite-diogenite (HED) 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
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.
The intense activity on Enceladus suggests a differentiated interior consisting of a rocky core, an internal ocean and an icy mantle. However, topography and gravity data suggests large heterogeneity in the interior, possibly including significant core topography. In the present study, we investigated the consequences of collisions with large impactors on the core shape.
We performed impact simulations using the code iSALE2D considering large differentiated impactors with radius ranging between 25 and 100 km and impact velocities ranging between 0.24 to 2.4 km/s. Our simulations showed that the main controlling parameters for the post-impact shape of Enceladus' rock core are the impactor radius and velocity and to a lesser extent the presence of an internal water ocean and the porosity and strength of the rock core. For low energy impacts, the impactors do not pass completely through the icy mantle. Subsequent sinking and spreading of the impactor rock core lead to a positive core topographic anomaly. For moderately energetic impacts, the impactors completely penetrate through the icy mantle, inducing a negative core topography surrounded by a positive anomaly of smaller amplitude. The depth and lateral extent of the excavated area is mostly determined by the impactor radius and velocity. For highly energetic impacts, the rocky core is strongly deformed, and the full body is likely to be disrupted. Explaining the long-wavelength irregular shape of Enceladus' core by impacts would imply multiple low velocity (< 2.4 km/s) collisions with deca-kilometric differentiated impactors, which is possible only after the LHB period.
Two principal meteorite groups are spectrally analogous with Hungaria background asteroids: unmelted L chondrites, and partially-melted primitive achondrites.
The past decade has seen a significant expansion both in the
interpretive methodologies used to extract mineralogical information
from asteroid spectra and other remote-sensing data and in the number of
asteroids for which mineralogical characterizations exist. Robust
mineralogical characterizations now exist for more than 40 asteroids, an
order of magnitude increase since Asteroids II was published. Such
characterizations have allowed significant progress to be made in the
identification of meteorite parent bodies. Although considerable
progress has been made, most asteroid spectra have still only been
analyzed by relatively ambiguous curvematching techniques. Where
appropriate and feasible, such data should be subjected to a
quantitative analysis based on diagnostic mineralogical spectral
features. The present paper reviews the recent advances in interpretive
methodologies and outlines procedures for their application.
We propose and analyze a new mechanism for the formation of the wide
asynchronous binary population. These binary asteroids have wide semi-major
axes relative to most near-Earth and Main Belt asteroid systems. Confirmed
members have rapidly rotating primaries and satellites that are not tidally
locked. Previously suggested formation mechanisms from impact ejecta, planetary
flybys and directly from rotational fission events cannot satisfy all of the
observations. The newly hypothesized mechanism works as follows: (i) these
systems are formed from rotational fission, (ii) their satellites are tidally
locked, (iii) their orbits are expanded by the BYORP effect, (iv) their
satellites de-synchronize due to the adiabatic invariance between the libration
of the secondary and the mutual orbit, and (v) the secondary avoids
resynchronization due to the the YORP effect. This seemingly complex chain of
events is a natural pathway for binaries with satellites that have particular
shapes, which define the BYORP effect torque that acts on the system. After
detailing the theory, we analyze each of the wide asynchronous binary members
and candidates to assess their most likely formation mechanism. Finally, we
suggest possible future observations to check and constrain our hypothesis.
We developed an orbital model of the satellites of (93) Minerva based on
Keck II AO observations recorded in 2009 and a mutual event between one
moon and the primary detected in March 2010. Using new lightcurves we
found an approximated ellipsoid shape model for the primary. With a
reanalysis of the IRAS data, we derived a preliminary bulk density of
1.5±0.2 g/cc. We will present a detailed analysis of the system,
including a 3D shape model of the 93 Minerva primary derived by
combining our AO observations, lightcurve, and stellar occultations.
Dactyl was discovered in solid state imaging (SSI) data on February 17, 1994, during the long playback of approach images from the Galileo spacecraft's encounter with the asteroid 243 Ida. Forty-seven images of the Ida–Dactyl pair were obtained. A detailed search for other satellites was made. No confirmed detections were made, all other candidate features being consistent with radiation hits. We deduce a manifold of osculating two-body orbits that approximate Dactyl's motion over the observed orbital arc depending on the assumed mass of Ida. At the time of Galileo's encounter, Dactyl was found to be 85 km from the center of Ida, moving at ∼6 m·sec−1in the same rection as Ida's retrograde spin. The inclination of its orbit is ∼172° in Ida's equatorial system (IAU definition). It was not possible to obtain a definitive orbit or measure of Ida's mass from the observed motion even though supplemental techniques (search for Dactyl's shadow on Ida, changes in angular diameter and brightness, and attempts to determine the spin of Dactyl) were explored. The influence of Ida's irregular gravitational field and solar perturbations on two-body motion are evaluated and found to be undetectable in the observed orbital arc. These effects may, however, strongly influence the motion over orbital time scales. Limits to the value of Ida's gravitation parameter,GM, are derived. A robust lower limit,GM> 0.0023 km3·sec−2, is obtained by requiring Dactyl's orbit to be bound. Hubble Space Telescope observations, which show no evidence of Dactyl on a hyperbolic orbit, excludes values ofGMin the range 0.00216 <GM< 0.0023 km3·sec−2. An upper limit,GM< 0.0031 km3·sec−2, deduced by requiring that the orbital motion has a long lifetime in a realistic approximation to Ida's gravitational field, is illustrated with numerical calculations. Ida's mass is therefore constrained to the range 4.2 ± 0.6 × 1019g, which, together with a volume of 16,100 ± 1900 km3(Thomas P. C., M. J. S. Belton, B. Carcich, C. R. Chapman, M. E. Davies, R. Sullivan, and J. Veverka 1996.Icarus120, 20–32.) yields a bulk density of 2.6 ± 0.5 g·cm−3(Belton, M. J. S., C. R. Chapman, P. C. Thomas, M. E. Davies, R. Greenberg, K. Klaasen, D. Byrnes, L. D'Amario, S. Synnott, T. V. Johnson, A. McEwen, W. Merline, D. R. Davis, J-M. Petit, A. Storrs, J. Veverka, and B. Zellner 1995.Nature374, 785–788.).
A systematic spectral analysis has been Carried out on a large subset (39 of 144) of the S-type asteroid population. The S-asteroid class includes a number of distinct compositional subtypes [designated S(I)-S(VII)] which exhibit surface silicate assemblages ranging from pure olivine (dunites) through olivine-pyroxene mixtures to pure pyroxene or pyroxene-feldspar mixtures (basalts). S-asteroid absorption bands are weaker than expected for pure mafic silicate assemblages, indicating the presence of an additional phase, most probably FeNi metal, although the abundance of metallic or feldspar components is not well constrained, The diversity within the S-class probably arises from several sources, including the coexistence of undifferentiated, partially differentiated, and fully differentiated bodies within the general S-asteroid population and the exposure of compositionally distinct units from within metamorphosed and partially and fully differentiated parent bodies. Partial differentiation within planetesimals appears to be an important source of this diversity. The surface assemblages of these subtypes include both analogues to known meteorite classes (e.g., pallasites, mesosiderites, ureilites, lodranites, brachinites, winonaites) and materials not sampled in our present meteorite collections. No specific ordinary chondrite parent bodies have been identified within the S-class, but silicate mineralogy provides a strong test for possible ordinary chondritic affinities. This test is failed by 75% of the S-asteroids. Only the S(IV)-subtype objects have silicates consistent with ordinary chondrites (OC). This subtype provides the only viable OC parent body candidates among the large main-belt S-asteroid population, although the individual objects remain to be evaluated. The S(IV) objects are concentrated near the 3:1 Kirkwood gap at 2.5 AU, and their ejecta can be readily injected into the associated chaotic region and rapidly converted into Earth-crossing orbits which may contribute to the high abundance of OC meteorites. S-asteroid absorption band depth correlates with asteroid diameter. It is relatively constant for objects larger than 100 km and increases steeply toward smaller sizes. This suggests that some equilibrium has been attained in the optical surfaces of S-asteroids larger than 100 km but not on smaller bodies.
Over time, exposure of airless bodies to the space environment results in optical changes to their surfaces. These optical changes are functions of the porosity, grain size distribution, and composition of the surface, and they depend on the relative rates of surface modification processes. Collectively, surface modification processes (such as impacts, solar wind ion implantation, sputtering, and micrometeorite bombardment) and their resulting optical effects have come to be known as "space weathering." Studies of lunar rocks and soils are the most important foundation we have on which to build an understanding of space weathering on asteroids. We cannot directly measure asteroid surfaces in a laboratory environment; therefore, we describe the lunar case, and compare it with the evidence for asteroids. In this chapter we review the evidence for space weathering on asteroids, including spectroscopy of optical effects, microscopy of physical effects, simulations of processes, lunar soils, meteorite breccias, spacecraft observations, and theoretical modeling. An understanding of space weathering is important to all remote-sensing studies of asteroid surfaces.
RELAB is a multiuser facility that provides high quality spectroscopy data (0.3 to 50 µm) without charge to scientists and students in NASA planetary exploration programs.
New data from observations of asteroid mutual perturbation events, observations of asteroid satellites, and spacecraft encounters have revolutionized our understanding of asteroid bulk density. Most asteroids appear to have bulk densities that are well below the grain density of their likely meteorite analogs. This indicates that many asteroids have significant porosity. High porosity attenuates shock propagation, strongly affecting the nature of cratering and greatly lengthening the collisional lifetimes of porous asteroids. Analysis of density trends suggests that asteroids are divided into three general groups: (1) asteroids that are essentially solid objects, (2) asteroids with macroporosities ~20% that are probably heavily fractured, and (3) asteroids with macroporosities >30% that are loosely consolidated "rubble pile" structures.
The distribution of asteroids across the Main Belt has been studied for
decades to understand the compositional distribution and what that tells us
about the formation and evolution of our solar system. All-sky surveys now
provide orders of magnitude more data than targeted surveys. We present a
method to bias-correct the asteroid population observed in the Sloan Digital
Sky Survey (SDSS) according to size, distance, and albedo. We taxonomically
classify this dataset consistent with the Bus and Bus-DeMeo systems and present
the resulting taxonomic distribution. The dataset includes asteroids as small
as 5 km, a factor of three in diameter smaller than in previous works. Because
of the wide range of sizes in our sample, we present the distribution by
number, surface area, volume, and mass whereas previous work was exclusively by
number. While the distribution by number is a useful quantity and has been used
for decades, these additional quantities provide new insights into the
distribution of total material. We find evidence for D-types in the inner main
belt where they are unexpected according to dynamical models of implantation of
bodies from the outer solar system into the inner solar system during planetary
migration (Levison et al. 2009). We find no evidence of S-types or other
unexpected classes among Trojans and Hildas, albeit a bias favoring such a
detection. Finally, we estimate for the first time the total amount of material
of each class in the inner solar system. The main belt's most massive classes
are C, B, P, V and S in decreasing order. Excluding the four most massive
asteroids, Ceres, Pallas, Vesta and Hygiea that heavily skew the values,
primitive material (C-, P-types) account for more than half main-belt and
Trojan asteroids by mass, most of the remaining mass being in the S-types. All
the other classes are minor contributors to the material between Mars and
Jupiter.
The Yarkovsky effect is a thermal radiation force that causes objects to undergo semimajor axis drift and spinup/spindown as a function of their spin, orbit, and material properties. This mechanism can be used to (1) deliver asteroids (and meteoroids) with diameter D < 20 km from their parent bodies in the main belt to chaotic resonance zones capable of transporting this material to Earth-crossing orbits, (2) disperse asteroid families, with drifting bodies jumping or becoming trapped in mean-motion and secular resonances within the main belt, and (3) modify the rotation rates of asteroids a few kilometers in diameter or smaller enough to possibly explain the excessive number of very fast and very slow rotators among the small asteroids. Accordingly, we suggest that nongravitational forces, which produce small but meaningful effects on aster- oid orbits and rotation rates over long timescales, should now be considered as important as collisions and gravitational perturbations to our overall understanding of asteroid evolution.
A set of 4000 numbered asteroids from the main belt are examined in
terms of size distribution with attention given to subsets of the
objects that relate to family membership and semimajor axis range. The
IRAS database is employed to estimate albedo and diameter, and non-IRAS
procedures are used check the albedo estimates. Nonfamily asteroids tend
toward distributions with a marked change in slope at diameters of about
150 km and with a differential power-law distribution exponent with
values of about 3 for large objects down to about 1 for small objects.
The findings are contradicted only by the Flora region in which the
sample is complete to sizes as small as 18 km and with a steep slope at
small sizes. The findings suggest that collisional evolution did not
play a significant role in the asteroidal evolution and that the
asteroids are fragments from catastrophic collisions.
We present images of two asteroid companions from adaptive optics (AO)
observations. These detections bring to four the number of binary
systems ever imaged, the previous discoveries being 243 Ida/Dactyl by
Galileo in 1993 (Belton et al./ 1995, Nature 374, 785) and 45
Eugenia/Petit-Prince in 1998 (Merline et al./ 1999, Nature 401, 565). A
satellite of 762 Pulcova was discovered on 2000 Feb 22 UT at the
Canada-France-Hawaii Telescope (CFHT) and was later confirmed by
additional observations at CFHT and Keck II. The satellite is about 4
mag fainter than the primary and our fit to the orbit indicates that it
was inclined approximately 60 deg to the line-of-sight, with a
semi-major axis of 800 km (0.6\arcsec) and a period of 4.0 days. We
derive a density for this FC-type primary of 1.8 g cm-3,
higher than our nominal value of 1.2 g cm-3 for F-type
Eugenia. On 2000 Aug 10 UT, Keck AO observations revealed that the
C-type 90 Antiope is a double asteroid, with similar-sized components,
separated by only 170 km (0.12\arcsec), with a brightness difference of
less than 0.1 mag. The co-orbiting pair was observed on 6 consecutive
nights and was found to have an orbital period of about 16.5 hours,
consistent with the established photometric ``rotation" period. While we
cannot rule out a very thin bridge of material connecting the two, we
show that it is not similar to the dumbbell-shaped 216 Kleopatra
reported by Ostro et al. 2000 (Science 288, 836). The two components are
clearly separated in the raw images, with a contrast consistent with the
PSF. We acquired similar images of Kleopatra before, during, and after
the radar observations of Ostro et al. Our Kleopatra images show a
bridge connecting the two components, but such a bridge is absent in our
Antiope images. This program is funded by NSF and NASA and uses CFHT
(French time), Keck Observatory (NASA time), and Mt. Wilson Observatory.
Spectra of asteroid 4 Vesta and 21 small (estimated diameters less than 10 km) asteroids with Vesta-like spectral properties (Vestoids) were measured at visible and near-infrared wavelengths (similar to0.44 to similar to1.65 mum). All of the measured small asteroids (except for 2579 Spartacus) have reflectance spectra consistent with surface compositions similar to eucrites and howardites and consistent with all being derived from Vesta. None of the observed asteroids have spectra similar to diogenites. We find no spectral distinction between the 15 objects tabulated as members of the Vesta dynamical family and 6 of the 7 sampled "non-family" members that reside just outside the semi-major axis (a), eccentricity (e), and inclination (i) region of the family. The spectral consistency and close orbital (a-e-i) match of these "non-family" objects to Vesta and the Vesta family imply that the true bounds of the family extend beyond the subjective cut-off for membership. Asteroid 2579 Spartacus has a spectrum consistent with a mixture of eucritic material and olivine. Spartacus could contain olivine-rich material from Vesta's mantle or may be unrelated to Vesta altogether. Laboratory measurements of the spectra of eucrites show that samples having nearly identical compositions can display a wide range of spectral slopes. Finer particle sizes lead to an increase in the slope, which is usually referred to as reddening. This range of spectral variation for the best-known meteoritic analogs to the Vestoids, regardless of whether they are actually related to each other, suggests that the extremely red spectral slopes for some Vestoids can be explained by very fine-grained eucritic material on their surfaces.
We provide an overview of the execution, data, and results of the solid state imaging (SSI) experiment at the encounter of the Galileo spacecraft with the asteroid 243 Ida. Ninety-six images of the asteroid, representing 18 time samples during a rotation period (4.633 h), were transmitted to Earth as a result of the UT 1993 August 28.70284 encounter. This provided coverage of ∼95% of the surface and achieved ground resolutions as high as 25 m/pixel. Coverage of most of Ida's surface is available in four colors, with limited regions in five colors, at resolutions up to 105 m/pixel. A natural satellite of Ida, called Dactyl, was discovered in a prograde (with respect to Ida's spin), near-equatorial, orbit moving slowly (∼ 6 m/sec) with a separation of 85 km from Ida.s
Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic
spectral features to specific surface mineralogies. The combination of
spectroscopy with albedos and diameters derived from thermal infrared
observations can increase the scientific return beyond that of the individual
datasets. To that end, we have completed a spectroscopic observing campaign to
complement the ExploreNEOs Warm Spitzer program that obtained albedos and
diameters of nearly 600 NEOs (Trilling et al. 2010). Here we present the
results of observations using the low-resolution prism mode (~0.7-2.5 microns)
of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also
include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF
Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared
spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our
survey and 213 observations of 154 objects from the MIT survey). We identify a
taxonomic class for each spectrum and use band parameter analysis to
investigate the mineralogies for the S-, Q-, and V-complex objects. Our
analysis suggests that for spectra that contain near-infrared data but lack the
visible wavelength region, the Bus-DeMeo system misidentifies some S-types as
Q-types. We find no correlation between spectral band parameters and
ExploreNEOs albedos and diameters. We find slightly negative Band Area Ratio
(BAR) correlations with phase angle for Eros and Ivar, but a positive BAR
correlation with phase angle for Ganymed. We find evidence for spectral phase
reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary
chondrite type analog for a subset of our sample. Our resulting proportions of
H, L, and LL ordinary chondrites differ from those calculated for meteorite
falls and in previous studies of ordinary chondrite-like NEOs.
Near-Earth Asteroids (NEAs) offer insight into a size range of objects that are not easily observed in the main asteroid belt. Previous studies on the diversity of the NEA population have relied primarily on modeling and statistical analysis to determine asteroid compositions. Olivine and pyroxene, the dominant minerals in most asteroids, have characteristic absorption features in the visible and near-infrared (VISNIR) wavelengths that can be used to determine their compositions and abundances. However, formulas previously used for deriving compositions do not work very well for ordinary chondrite assemblages. Because two-thirds of NEAs have ordinary chondrite-like spectral parameters, it is essential to determine accurate mineralogies. Here we determine the band area ratios and Band I centers of 72 NEAs with visible and near-infrared spectra and use new calibrations to derive the mineralogies 47 of these NEAs with ordinary chondrite-like spectral parameters. Our results indicate that the majority of NEAs have LL-chondrite mineralogies. This is consistent with results from previous studies but continues to be in conflict with the population of recovered ordinary chondrites, of which H chondrites are the most abundant. To look for potential correlations between asteroid size, composition, and source region, we use a dynamical model to determine the most probable source region of each NEA. Model results indicate that NEAs with LL chondrite mineralogies appear to be preferentially derived from the ν6 secular resonance. This supports the hypothesis that the Flora family, which lies near the ν6 resonance, is the source of the LL chondrites. With the exception of basaltic achondrites, NEAs with non-chondrite spectral parameters are slightly less likely to be derived from the ν6 resonance than NEAs with chondrite-like mineralogies. The population of NEAs with H, L, and LL chondrite mineralogies does not appear to be influenced by size, which would suggest that ordinary chondrites are not preferentially sourced from meter-sized objects due to Yarkovsky effect.
The Sloan Digital Sky Survey (SDSS) Moving Object Catalog contains spectrophotometric information for thousands of asteroids, presenting the opportunity to probe objects much fainter than are typically reached in spectroscopic surveys. Using two different approaches, it is estimated that 30 ± 5% of the C-complex asteroids in the SDSS have a 0.7-μm band, implying that roughly two-thirds will have a 3-μm absorption band and hydrated minerals based on correlations between those two absorptions found by Howell et al. (Howell, E.S. et al. [2011]. EPSC-DPS Joint Meeting, p. 637). In an effort to avoid confusion with formal taxonomies, I call these objects Ch∼ in this work, with the C∼ group defined as those without evidence of a 0.7-μm band. This fraction appears fairly stable with solar distance, although there is evidence it is higher in the middle asteroid belt (2.50–2.82 AU) than outside those bounds. In the size range covered by the SDSS dataset, the Ch∼ fraction is most consistent with a flat distribution. Inclusion of the SMASS and S3OS2 datasets suggests an overall minimum in Ch∼ fraction from H ∼ 12–14, though this distribution may be biased by the solar distance variation mentioned above.
We collected mid-IR spectra from 5.2 to 38 μm using the Spitzer Space Telescope Infrared Spectrograph of 28 asteroids representative of all established types of binary groups. Photometric lightcurves were also obtained for 14 of them during the Spitzer observations to provide the context of the observations and reliable estimates of their absolute magnitudes. The extracted mid-IR spectra were analyzed using a modified standard thermal model (STM) and a thermophysical model (TPM) that takes into account the shape and geometry of the large primary at the time of the Spitzer observation. We derived a reliable estimate of the size, albedo, and beaming factor for each of these asteroids, representing three main taxonomic groups: C, S, and X. For large (volume-equivalent system diameter Deq > 130 km) binary asteroids, the TPM analysis indicates a low thermal inertia (Γ ⩽ ∼100 J s−1/2 K−1 m−2) and their emissivity spectra display strong mineral features, implying that they are covered with a thick layer of thermally insulating regolith. The smaller (surface-equivalent system diameter Deff < 17 km) asteroids also show some emission lines of minerals, but they are significantly weaker, consistent with regoliths with coarser grains, than those of the large binary asteroids. The average bulk densities of these multiple asteroids vary from 0.7–1.7 g/cm3 (P-, C-type) to ∼2 g/cm3 (S-type). The highest density is estimated for the M-type (22) Kalliope (3.2 ± 0.9 g/cm3). The spectral energy distributions (SEDs) and emissivity spectra, made available as a supplement document, could help to constrain the surface compositions of these asteroids.
The equations to derive pyroxene compositions from absorption band positions in asteroid spectra (Gaffey et al. 2002) fail when applied to ordinary chondrite spectra. A method and a set of correction factors are defined to remedy this shortcoming.
This dataset contains the visible spectra of 820 asteroids obtained between November 1996 and May 2001 at the 1.52m telescope at ESO (La Silla). The useful spectral range is between about 4900 and 9200 Angstroms. The global spatial distribution of the objects covers the region between 2.2 and 3.3 AU. Some concentrations are apparent, since part of the survey was focused on particuarly interesting groups or families of asteroids. The observed asteroids have been classified according to the Tholen and the Bus taxonomies, with a good agreement between both in most of the cases. These data are presented and discussed in Lazarro et al. (2004).
We present a model of near-Earth asteroid (NEA) rotational fission and ensuing dynamics that describes the creation of synchronous binaries and all other observed NEA systems including: doubly synchronous binaries, high-e binaries, ternary systems, and contact binaries. Our model only presupposes the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, “rubble pile” asteroid geophysics, and gravitational interactions. The YORP effect torques a “rubble pile” asteroid until the asteroid reaches its fission spin limit and the components enter orbit about each other (Scheeres, D.J. [2007]. Icarus 189, 370–385). Non-spherical gravitational potentials couple the spin states to the orbit state and chaotically drive the system towards the observed asteroid classes along two evolutionary tracks primarily distinguished by mass ratio. Related to this is a new binary process termed secondary fission – the secondary asteroid of the binary system is rotationally accelerated via gravitational torques until it fissions, thus creating a chaotic ternary system. The initially chaotic binary can be stabilized to create a synchronous binary by components of the fissioned secondary asteroid impacting the primary asteroid, solar gravitational perturbations, and mutual body tides. These results emphasize the importance of the initial component size distribution and configuration within the parent asteroid. NEAs may go through multiple binary cycles and many YORP-induced rotational fissions during their approximately 10Myr lifetime in the inner Solar System. Rotational fission and the ensuing dynamics are responsible for all NEA systems including the most commonly observed synchronous binaries.
Non-destructive, non-contaminating, and relatively simple procedures can be used to measure the bulk density, grain density, and porosity of meteorites. Most stony meteorites show a relatively narrow range of densities, but differences within this range can be useful indicators of the abundance and oxidation state of iron and the presence or absence of volatiles. Typically, ordinary chondrites have a porosity of just under 10%, while most carbonaceous chondrites (with notable exceptions) are more than 20% porous. Such measurements provide important clues to the nature of the physical processes that formed and evolved both the meteorites themselves and their parent bodies. When compared with the densities of small solar system bodies, one can deduce the nature of asteroid and comet interiors, which in turn reflect the accretional and collisional environment of the early solar system.
Spin-allowed Fe z+ absorption bands occur in the visible and near-infrared diffuse reflectance spectra of most pyroxenes. The wavelengths of the bands centered near 1 #m and 2 #m vary as functions of pyroxene composition, making possible mineralogical and chemical deductions based on spectral reflectance curves. Typically, pyroxene bands are well developed in relation to absorption features in the spectra of other rock-forming minerals and glass; thus pyroxene often dominates the spectral curves of pyroxenebearing rocks. Telescopic spectra of the moon and some other solar system objects contain absorption features that can be interpreted in terms of pyroxenes mixed with other minerals and/or glass.
We present new near-infrared spectra of 20 Trojan asteroids. The spectra were recorded at the NASA Infrared Telescope Facility (IRTF) using the recently commissioned medium-resolution spectrograph SpeX and at the Multiple Mirror Telescope (MMT) using the instrument FSPEC. Spectra of all of these objects were measured in K-band (1.95–2.5 μm), 8 of these in L-band (2.8–4.0 μm), and 14 in the range 0.8–2.5 μm. These observations nearly double the number of published 0.8–2.5 μm spectra of Trojan asteroids and provide the first systematic study of the L-band region for these distant asteroids. The data show that the red spectral slope measured in the near-IR extends through the L-band, though it is not as steep here as at shorter wavelengths. A significant diversity is apparent in the near-IR spectral slopes of this sampling of objects. Most of the spectra do not contain any definitive absorption features characteristic of surface composition (e.g., H2O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. A few objects may display spectral activity, and the reliability of these possible features is discussed. While these spectra are generally compatible with silicate surfaces to explain the spectral slope mixed with some fraction of low albedo material, there is no absolute indication of silicates. The spectral slope could also be explained by the presence of hydrocarbons, but the lack of absorption features, especially in L-band where very strong fundamental absorptions from these molecules appear, constrains the character and abundance of these materials at the surface.
Extensive collection efforts in Antarctica and the Sahara in the past 10 years have greatly increased the number of known meteorites. Groupings of meteorites according to petrologic, mineralogical, bulk- chemical, and isotopic properties suggest the existence of 100-150 distinct parent bodies. Dynamical studies imply that most meteorites have their source bodies in the main belt and not among the near-Earth asteroids. Spectral observations of asteroids are currently the primary way of determining asteroid mineralogies. Linkages between ordinary chondrites and S asteroids, CM chondrites and C-type asteroids, the HEDs and 4 Vesta, and iron meteorites, enstatite chondrites, and M asteroids are discussed. However, it is difficult to conclusively link most asteroids with particular meteorite groups due to the number of asteroids with similar spectral properties and the uncertainties in the optical, chemical, and physical properties of the asteroid regolith.
Existing reflectance spectra of CI chondrites (18 spectra of 3 CIs) have been augmented with new (18 spectra of 2 CIs) reflectance spectra to ascertain the spectral variability of this meteorite class and provide insights into their spectral properties as a function of grain size, composition, particle packing, and viewing geometry. Particle packing and viewing geometry effects have not previously been examined for CI chondrites. The current analysis is focused on the 0.3-2.5 mum interval, as this region is available for the largest number of CI spectra. Reflectance spectra of powdered CI1 chondrites are uniformly dark (
The Goodman Spectrograph is an imaging, multi-object spectrograph for the SOuthern Astrophysical Research telescope (SOAR). It is one of the first designed to take advantage of Volume Phase Holographic (VPH) gratings by employing an articulated camera. This aspect of the mechanical design has had complicating effects on a number of usually simple systems, and has led to some unorthodox solutions. The spectrograph is also highly optimized for efficiency from 320 to 850 nm, and designed for rapid configuration changes, so that its throughput makes it competitive with instruments on larger telescopes. We present the high level requirements that have driven the mechanical and electronic systems, and show their implementation in the completed instrument. It is too early to assess the overall system performance, but tests of the modular subsystems show promising results. We discuss the expected overall performance and discuss mitigation strategies should that performance fall short of our goals.
In-situ investigation of asteroids is the next logical step in understanding their exact surface mineralogy, petrology, elemental abundances, particle size distribution, internal structure, and collisional evolution. Near-Earth asteroids (NEAs) provide us with ample opportunities for in-situ scientific exploration with lower Δv requirements and subsequently lower costs than their main belt counterparts. The ASTEX mission concept aims at surface characterization of two compositionally diverse NEAs, one with primitive and the other with a strong thermally evolved surface mineralogy. Here we present the first results of our ground-based characterization of potential ASTEX mission targets using the SpeX instrument on the NASA IRTF. Of the four potential targets we characterized, two (1991 JW and 1998 PA) have compositions similar to ordinary chondrite mineralogy. The other two targets (1994 CC and 1999 TA10) are thermally evolved objects with igneous formation histories. While 1994 CC is a triplet system and thus very challenging to orbit the V-type NEA, 1999 TA10 is the most interesting scientific ASTEX target identified so far.
We present visible-wavelength (0.435–0.925 μm) spectroscopic measurements for 1341 main-belt asteroids observed during the second phase of the Small Main-belt Asteroid Spectroscopic Survey (SMASSII). The purpose of this survey is to provide a new basis for studying the compositional structure of the asteroid belt. Through the large sample size and the relatively high spectral resolution (R∼100) of the SMASSII data, we find that values of the spectral parameters describing these data form more of a continuum than previously realized. Objects with intermediate spectral characteristics are bridging gaps that once separated distinct spectral classes. In some cases, newly revealed small-scale spectral features may be indicative of previously unrecognized mineral constituents. Here we present the data and principal component analyses that describe the SMASSII spectra. A companion paper utilizes these principal component scores, along with other measures of the spectral features, to develop a new taxonomy that takes advantage of the information contained within charge-coupled device spectra.
Visible wavelength spectra have been obtained for 1189 main-belt
asteroids during the second phase of the Small Main-belt Asteroid
Spectroscopic Survey. These telescopic measurements were made using
charge-coupled device (CCD) detectors, allowing for the targeting of
smaller asteroids. A majority of the asteroids sampled have estimated
diameters of 30 km or less. The SMASSII survey provides the largest
internally-consistent sample of asteroid spectra ever obtained, and
reveals a greater range of spectral diversity among asteroids than has
been previously shown. The larger sample size, greater spectral
resolution, and greater photometric precision of the SMASSII survey,
compared with the most extensive previous survey, provide a basis for
developing a new ``feature-based'' taxonomic classification system for
asteroids. This new taxonomy builds on the robust, large-scale structure
of existing taxonomies, and relies on the presence or absence of
specific spectral features to define new class boundaries. The SMASSII
measurements reveal that many of the previous taxonomic classes that
appeared to be distinctly separate, are instead spanned by a nearly
continuous transition of spectral properties. This continuum may be
evidence of sampling a more complete range of mineralogies. A subset of
465 SMASSII asteroids were specifically targeted to test the genetic
reality of small dynamical ``families.'' These families likely result
from the collisional disruption of larger parent asteroids, and are
identified as clusters of objects having similar orbital parameters. The
targeted region, encompassing the heliocentric distance range of 2.690
to 2.815 AU, contains 14 families that had been previously identified,
based on numerous analyses of orbital distributions in this region of
the main belt. A newly developed multivariate technique that analyzes
the combination of spectral characteristics and orbital parameters
reveals that all 14 of these previously proposed families are distinct
from the ``background'' population of asteroids. This result implies
that each of these families is likely to have been truly formed by a
collisional event, providing strong evidence for an extensive
collisional history within the asteroid belt. C- and S-type asteroids
appear equally capable of forming families. Each family is found to be
relatively homogeneous in its spectral characteristics, allowing the
boundaries of the families, and potential interlopers, to be more
precisely identified than was possible in previous dynamical analyses.
The relative spectral homogeneity within each of these families provides
little evidence for any to have been formed from a differentiated parent
body. (Copies available exclusively from MIT Libraries, Rm. 14-0551,
Cambridge, MA 02139- 4307. Ph. 617-253-5668; Fax 617-253-1690.)
(Abstract shortened by UMI.)
We use high-resolution HED spectra and detailed compositional analyses
to derive formulas for determining their average pyroxene mineralogies.
DURING its reconnaissance of the asteroid 243 Ida, the Galileo spacecraft returned images of a second object, 1993(243)1 Dactyl1— the first confirmed satellite of an asteroid. Sufficient data were obtained on the motion of Dactyl to determine its orbit as a function of Ida's mass. Here we apply statistical and dynamical arguments to constrain the range of possible orbits, and hence the mass of Ida. Combined with the volume of Ida2, this yields a bulk density of 2.6 ± 0.5 g cm−3. Allowing for the uncertainty in the porosity of Ida, this density range is consistent with a bulk chon-dritic composition, and argues against some (but not all) classes of meteoritic igneous rock types that have been suggested as compositionally representative of S-type asteroids like Ida.
The majority of Near Earth Objects (NEOs) originated in collisions between bodies in the main asteroid belt and have found their way into near Earth space via complex and little understood dynamical interactions. This transport of material from the main belt into the inner Solar System has shaped the histories of the terrestrial planets. However, despite their scientific importance, key characteristics of the NEO population remain largely unexplored; some 99% of all presently known NEOs are essentially uncharacterized. We have an accepted Warm Spitzer Exploration Science Program (PI: Trilling) that allocates 500 hours of Spitzer time to observe ~700 NEOs. We will measure (1) the size distribution of this population; (2) the fraction of NEOs likely to be dead comets; (3) the albedo distribution of NEOs. We propose to gather spectroscopic data from a variety of telescopic facilities in order to physically characterize a significant subset of this Warm Spitzer NEO sample. By combining the size and albedo information from Spitzer with the compositional information from telescope spectroscopy we hope to shed light on several questions about the evolution and origin of the near-Earth asteroid population.
Abstract– We evaluate the chemical and physical conditions of metamorphism in ordinary chondrite parent bodies using X-ray diffraction (XRD)-measured modal mineral abundances and geochemical analyses of 48 type 4–6 ordinary chondrites. Several observations indicate that oxidation may have occurred during progressive metamorphism of equilibrated chondrites, including systematic changes with petrologic type in XRD-derived olivine and low-Ca pyroxene abundances, increasing ratios of MgO/(MgO+FeO) in olivine and pyroxene, mean Ni/Fe and Co/Fe ratios in bulk metal with increasing metamorphic grade, and linear Fe addition trends in molar Fe/Mn and Fe/Mg plots. An aqueous fluid, likely incorporated as hydrous silicates and distributed homogeneously throughout the parent body, was responsible for oxidation. Based on mass balance calculations, a minimum of 0.3–0.4 wt% H2O reacted with metal to produce oxidized Fe. Prior to oxidation the parent body underwent a period of reduction, as evidenced by the unequilibrated chondrites. Unlike olivine and pyroxene, average plagioclase abundances do not show any systematic changes with increasing petrologic type. Based on this observation and a comparison of modal and normative plagioclase abundances, we suggest that plagioclase completely crystallized from glass by type 4 temperature conditions in the H and L chondrites and by type 5 in the LL chondrites. Because the validity of using the plagioclase thermometer to determine peak temperatures rests on the assumption that plagioclase continued to crystallize through type 6 conditions, we suggest that temperatures calculated using pyroxene goethermometry provide more accurate estimates of the peak temperatures reached in ordinary chondrite parent bodies.
Abstract– Powder X-ray diffraction (XRD) is used to quantify the modal abundances (in wt%) of 18 H, 17 L, and 13 LL unbrecciated ordinary chondrite falls, which represents the complete petrologic range of equilibrated ordinary chondrites (types 4–6). The XRD technique presents an effective alternative to traditional methods for determining modal abundances, such as optical point counting and electron microprobe phase (EMP) mapping. The majority of chondrite powders in this study were previously prepared for chemical characterization from 8 to 20 g of material, which is consistent with the suggested mass (10 g) necessary to provide representative sampling of ordinary chondrites. Olivine and low-Ca pyroxene are the most abundant phases present, comprising one-half to three-fourths of total abundances, while plagioclase, high-Ca pyroxene, troilite, and metal comprise the remaining XRD-measured mineralogy. Pigeonite may also be present in some samples, but it is fitted using a high-Ca pyroxene standard, so exact abundances cannot be measured directly using XRD. Comparison of XRD-measured abundances with calculated Cross, Iddings, Pirsson, Washington (CIPW) normative abundances indicates that systematic discrepancies exist between these two data sets, particularly in olivine and high-Ca pyroxene. This discrepancy is attributed to the absence of pigeonite as a possible phase in the CIPW normative mineralogy. Oxides associated with pigeonite are improperly allocated, resulting in overestimated normative olivine abundances and underestimated normative high-Ca pyroxene abundances. This suggests that the CIPW norm is poorly suited for determining mineralogical modal abundances of ordinary chondrites.
Abstract— We have calculated pyroxene mineralogies of seven near-Earth asteroids (NEAs) with reflectance spectra similar to HEDs (howardites, eucrites, and diogenites). Two different sets of formulas (Gaffey et al. 2002; Burbine et al. 2007) are used to calculate the pyroxene mineralogies of the NEAs from their Band I and II centers. The band centers have been adjusted to compensate for the low temperatures on the asteroid surfaces. All of the derived mineralogies from the Gaffey et al. (2002) formulas and the Burbine et al. (2007) formulas overlap. The derived wollastonite (Wo) contents are very similar with differences being only approximately 1 mol%. The derived ferrosilite (Fs) contents differ by only 3 to 8 mol%. The determined pyroxene mineralogies for all seven near-Earth vestoids are consistent with eucrites or howardites. None of the objects have pyroxene mineralogies consistent with diogenites. The absence of near-Earth vestoids with pyroxene mineralogies similar to diogenites may indicate that it is difficult to produce sizeable (km-sized or larger) bodies that are predominantly composed of diogenitic material, suggesting these objects are rubble piles of mixed ejecta.