388 research outputs found
Composition of Near-Earth Asteroid 2008 EV5: Potential target for Robotic and Human Exploration
We observed potentially hazardous asteroid (PHA) 2008 EV5 in the visible
(0.30-0.92 microns) and near-IR (0.75-2.5 microns) wavelengths to determine its
surface composition. This asteroid is especially interesting because it is a
potential target for two sample return mission proposals (Marco Polo-R and
Hayabusa-2) and human exploration due to its low delta-v for rendezvous. The
spectrum of 2008 EV5 is essentially featureless with exception of a weak
0.48-microns spin-forbidden Fe3+ absorption band. The spectrum also has an
overall blue slope. The albedo of 2008 EV5 remains uncertain with a lower limit
at 0.05 and a higher end at 0.20 based on thermal modeling. The Busch et al.
(2011) albedo estimate of 0.12 is consistent with our thermal modeling results.
The albedo and composition of 2008 EV5 are also consistent with a C-type
taxonomic classification (Somers et al. 2008). The best spectral match is with
CI carbonaceous chondrites similar to Orgueil, which also have a weak
0.48-microns feature and an overall blue slope. This 0.48-microns feature is
also seen in the spectrum of magnetite. The albedo of CI chondrites is at the
lower limit of our estimated range for the albedo of 2008 EV5.Comment: Pages: 19 Figures: 6 Tables:
Spectral reflectance of carbonate minerals and rocks in the visible and near infrared (0.35 - 2.55 microns) and its applications in carbonate petrology
Reflection spectroscopy in the visible and near infrared (0.35 to 2.55 micron) offers a rapid, inexpensive, nondestructive tool for determining the mineralogy and investigating the minor element chemistry of the hard-to-discriminate carbonate minerals, and can, in one step, provide information previously obtainable only by the combined application of two or more analytical techniques. When light interacts with a mineral certain wavelengths are preferentially absorbed. The number, positions, widths and relative intensities of these absorptions are diagnostic of the mineralogy and chemical composition of the sample. At least seven bands due to vibrations of the carbonate radical occur between 1.60 and 2.55 micron. Positions of these bands vary from one carbonae mineral to another and can be used for mineral identification. Cation mass is the primary factor controlling band position; cation radius plays a secondary role
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Sexual well-being and diurnal cortisol after prostate cancer treatment.
Sexual dysfunction and psychological distress are common after prostate cancer. Research has not examined the role of neuroendocrine markers of stress (e.g. cortisol). This study examines whether sexual functioning or sexual bother is associated with diurnal cortisol. Men treated for prostate cancer completed the University of California-Los Angeles Prostate Cancer Index and provided saliva samples four times daily for cortisol assessment. Higher sexual bother, but not sexual functioning, was associated with steeper cortisol slope. Better sexual functioning, and not sexual bother, was significantly associated with the cortisol awakening response. Assessment of stress and stress-reducing interventions might be warranted in sexual rehabilitation after prostate cancer
An initial perspective of S-asteroid subtypes within asteroid families
Many main belt asteroids cluster around certain values of semi-major axis (a), inclination (i), and eccentricity (e). Hirayama was the first to notice these concentrations which he interpreted as evidence of disruptions of larger parent bodies. He called these clusters 'asteroid families'. The term 'families' is increasingly reserved for genetic associations to distinguish them from clusters of unknown or purely dynamical origin (e.g. the Phocaea cluster). Members of a genetic asteroid family represent fragments derived from various depths within the original parent planetesimal. Thus, family members offer the potential for direct examination of the interiors of parent bodies which have undergone metamorphism and differentiation similar to that occurring in the inaccessible interiors of terrestrial planets. The differentiation similar to that occurring in the inaccessible interiors of terrestrial planets. The condition that genetic family members represent the fragments of a parent object provides a critical test of whether an association (cluster in proper element space) is a genetic family. Compositions (types and relative abundances of materials) of family members must permit the reconstruction of a compositionally plausible parent body. The compositions of proposed family members can be utilized to test the genetic reality of the family and to determine the type and degree of internal differentiation within the parent planetesimal. The interpretation of the S-class mineralogy provides a preliminary evaluation of family memberships. Detailed mineralogical and petrological analysis was done based on the reflectance spectra of 39 S-type asteroids. The result is a division of the S-asteroid class into seven subtypes based on compositional differences. These subtypes, designated S(I) to S(VII), correspond to surface silicate assemblages ranging from monomineralic olivine (dunites) through olivine-pyroxene mixtures to pure pyroxene or pyroxene-feldspar mixtures (basalts). The most general conclusion is that the S-asteroids cannot be treated as a single group of objects without greatly oversimplifying their properties. Each S-subtype needs to be treated as an independent group with a distinct evolutionary history
Iron oxide bands in the visible and near-infrared reflectance spectra of primitive asteroids
High resolution reflectance spectra of primitive asteroids (C, P, and D class and associated subclasses) have commonly revealed an absorption feature centered at 0.7 microns attributed to an Fe(2+)-Fe(3+) charge transfer transition in iron oxides and/or oxidized iron in phyllosilicates. A smaller feature identified at 0.43 microns has been attributed to an Fe(3+) spin-forbidden transition in iron oxides. In the spectra of the two main-belt primitive asteroids 368 Haidea (D) and 877 Walkure (F), weak absorption features which were centered near the location of 0.60-0.65 microns and 0.80-0.90 microns prompted a search for features at these wavelengths and an attempt to identify their origin(s). The CCD reflectance spectra obtained between 1982-1992 were reviewed for similar absorption features located near these wavelengths. The spectra of asteroids in which these absorption features have been identified are shown. These spectra are plotted in order of increasing heliocentric distance. No division of the asteroids by class has been attempted here (although the absence of these features in the anhydrous S-class asteroids, many of which have presumably undergone full heating and differentiation should be noted). For this study, each spectrum was treated as a continuum with discrete absorption features superimposed on it. For each object, a linear least squares fit to the data points defined a simple linear continuum. The linear continuum was then divided into each spectrum, thus removing the sloped continuum and permitting the intercomparison of residual spectral features
NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results
The NEOWISE dataset offers the opportunity to study the variations in albedo
for asteroid classification schemes based on visible and near-infrared
observations for a large sample of minor planets. We have determined the
albedos for nearly 1900 asteroids classified by the Tholen, Bus and Bus-DeMeo
taxonomic classification schemes. We find that the S-complex spans a broad
range of bright albedos, partially overlapping the low albedo C-complex at
small sizes. As expected, the X-complex covers a wide range of albedos. The
multi-wavelength infrared coverage provided by NEOWISE allows determination of
the reflectivity at 3.4 and 4.6 m relative to the visible albedo. The
direct computation of the reflectivity at 3.4 and 4.6 m enables a new
means of comparing the various taxonomic classes. Although C, B, D and T
asteroids all have similarly low visible albedos, the D and T types can be
distinguished from the C and B types by examining their relative reflectance at
3.4 and 4.6 m. All of the albedo distributions are strongly affected by
selection biases against small, low albedo objects, as all objects selected for
taxonomic classification were chosen according to their visible light
brightness. Due to these strong selection biases, we are unable to determine
whether or not there are correlations between size, albedo and space
weathering. We argue that the current set of classified asteroids makes any
such correlations difficult to verify. A sample of taxonomically classified
asteroids drawn without significant albedo bias is needed in order to perform
such an analysis.Comment: Accepted to Ap
Composition of the L5 Mars Trojans: Neighbors, not Siblings
Mars is the only terrestrial planet known to have Tro jan (co-orbiting)
asteroids, with a confirmed population of at least 4 objects. The origin of
these objects is not known; while several have orbits that are stable on
solar-system timescales, work by Rivkin et al. (2003) showed they have
compositions that suggest separate origins from one another. We have obtained
infrared (0.8-2.5 micron) spectroscopy of the two largest L5 Mars Tro jans, and
confirm and extend the results of Rivkin et al. (2003). We suggest that the
differentiated angrite meteorites are good spectral analogs for 5261 Eureka,
the largest Mars Trojan. Meteorite analogs for 101429 1998 VF31 are more varied
and include primitive achondrites and mesosiderites.Comment: 14 manuscript pages, 1 table, 6 figures. To be published in Icarus.
See companion paper 0709.1921 by Trilling et a
Spectroscopic Survey of X-type Asteroids
We present reflected light spectral observations from 0.4 to 2.5 micron of 24
asteroids chosen from the population of asteroids initially classified as
Tholen X-type objects (Tholen, 1984). The X complex in the Tholen taxonomy
comprises the E, M and P classes which have very different inferred
mineralogies but which are spectrally similar to each other, with featureless
spectra in visible wavelengths. The data were obtained during several observing
runs in the 2004-2007 years at the NTT, TNG and IRTF telescopes. We find a
large variety of near-infrared spectral behaviors within the X class, and we
identify weak absorption bands in spectra of 11 asteroids. Our spectra,
together with albedos published by Tedesco et al. (2002), can be used to
suggest new Tholen classifications for these objects. In order to constrain the
possible composition of these asteroids, we perform a least-squares search
through the RELAB spectral database. Many of the best fits are consistent with
meteorite analogue materials suggested in the published literature. In fact, we
find that 7 of the new M-types can be fit with metallic iron (or pallasite)
materials, and that the low albedo C/P-type asteroids are best fitted with CM
meteorites, some of which have been subjected to heating episodes or laser
irradiation. Finally, we consider and analyse the sample of the X-type
asteroids we have when we combine the present observations with previously
published observations for a total of 72 bodies.Comment: Accepted for publication in Icaru
First albedo determination of 2867 Steins, target of the Rosetta mission
We present the first albedo determination of 2867 Steins, the asteroid target
o f the Rosetta space mission together with 21 Lutetia. The data were obtained
in polarimetric mode at the ESO-VLT telescope with the FORS1 instrument in the
V and R filters. Observations were carried out from Jun e to August 2005
covering the phase angle range from 10.3 deg. to 28.3 deg., allowing the
determination of the asteroid albedo by the well known experimenta l
relationship between the albedo and the slope of the polarimetric curve at th e
inversion angle. The measured polarization values of Steins are small,
confirming an E-type cla ssification for this asteroid, as already suggested
from its spectral propertie s. The inversion angle of the polarization curve in
the V and R filters is resp ectively of 17.3 +/-1.5deg. and 18.4+/-1.0 deg.,
and the corresponding sl ope parameter is of 0.037+/-0.003 %/deg and
0.032+/-0.003 %/deg. On the basis of its polarimetric slope value, we have
derived an albedo of 0.45 +/-0.1, that gives an estimated diameter of 4.6 km,
assuming an absolute V ma gnitude of 13.18 mag.Comment: 4 pages, 4 figures, letter accepted for pubblication on A&
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