The mineralogy of Vesta, based on data obtained by the Dawn spacecraft's visible and infrared spectrometer, is consistent with howardite-eucrite-diogenite meteorites. There are considerable regional and local variations across the asteroid: Spectrally distinct regions include the south-polar Rheasilvia basin, which displays a higher diogenitic component, and equatorial regions, which show a higher eucritic component. The lithologic distribution indicates a deeper diogenitic crust, exposed after excavation by the impact that formed Rheasilvia, and an upper eucritic crust. Evidence for mineralogical stratigraphic layering is observed on crater walls and in ejecta. This is broadly consistent with magma-ocean models, but spectral variability highlights local variations, which suggests that the crust can be a complex assemblage of eucritic basalts and pyroxene cumulates. Overall, Vesta mineralogy indicates a complex magmatic evolution that led to a differentiated crust and mantle.
"Products of high-temperature episodes in the solar system materials other than the terrestrial planets are represented by the differentiated achondrites. The mineralogy of Vesta, based on data obtained by the Dawn Mission (De Sanctis et al. 2012), is consistent with HED achondrites and confirmed the presence of the proposed layered crust model (Takeda 1979). It is important to recognize that high-temperature events took place in a region of the LL chondrite parent body, from where Itokawa and parent asteroids of the Antarctic meteorites were ejected. "
[Show abstract][Hide abstract] ABSTRACT: Mineralogy of three LL chondrites including Y-981971, Y-793214, and Y-790782 indicates that granulitic materials may have been formed in some depth of their parent body by an impact event. This process of high-temperature episodes is different from the records in the differentiated achondrites (howardite-eucrite-diogenite (HED)) possibly from the Vesta-like asteroid.
"Radiometrically dated samples from known locations on planetary surfaces have only been obtained for Earth and the Moon. Meteorites from asteroids, the Moon, and Mars have been dated by radiometric techniques, but except for the howardite–eucrite–diogenite (HED) meteorites which are now known to have been blasted off asteroid 4 Vesta during formation of the 505- km-diameter Rheasilivia impact basin ~10 9 years ago (DeSanctis et al., 2012; Schenk et al., 2012) (Fig. 18), the locations from which these meteorites originated are unknown and, thus, cannot be used to age-date a specific geologic unit. Impact craters, however, have been forming on solid-surfaced bodies since shortly after our solar system began to take shape. "
[Show abstract][Hide abstract] ABSTRACT: Impact cratering is the one geologic process which is common to all solar system objects. Impact craters form by the resulting explosion between a solar system body and hypervelocity objects. Comparison with craters formed by chemical and nuclear explosions reveals that crater diameter is related to other morphometric characteristics of the crater, such as depth and rim height. These relationships allow scientists to use impact craters to probe the subsurface structure within the upper few kilometer of a planetary surface and to estimate the amounts and types of degradational processes which have affected the planet since crater formation. Crater size-frequency distribution analysis provides the primary mechanism for determining ages of planetary terrains and constraining the timing of resurfacing episodes. Thus, impact craters provide many important insights into the evolution of planetary surfaces.
"Much of the surface shows a howardite-like spectrum intermixed with smaller-scale regions resembling eucrites and diogenites. The south polar region (Rheasilvia), a large impact basin, is consistent with more Mg-rich pyroxene characteristic of diogenites (De Sanctis et al. 2012). These spectral variations are indicative of a differentiated crust where the deeper diogenitic materials have been exposed through impact. "
[Show abstract][Hide abstract] ABSTRACT: We have determined the mid-IR optical constants of one alkali feldspar and four pyroxene compositions in the range of 250–4000
cm−1. Measured reflectance spectra of oriented single crystals were iteratively fit to modeled spectra derived from classical
dispersion analysis. We present the real and imaginary indices of refraction (n and k) along with the oscillator parameters with which they were modeled. While materials of orthorhombic symmetry and higher are
well covered by the current literature, optical constants have been derived for only a handful of geologically relevant monoclinic
materials, including gypsum and orthoclase. Two input parameters that go into radiative transfer models, the scattering phase
function and the single scattering albedo, are functions of a material’s optical constants. Pyroxene is a common rock-forming
mineral group in terrestrial bodies as well as meteorites and is also detected in cosmic dust. Hence, having a set of pyroxene
optical constants will provide additional details about the composition of Solar System bodies and circumstellar materials.
We follow the method of Mayerhöfer et al. (2010), which is based on the Berreman 4 × 4 matrix formulation. This approach provides a consistent way to calculate the reflectance
coefficients in low-symmetry cases. Additionally, while many models assume normal incidence to simplify the dispersion relations,
this more general model applies to reflectance spectra collected at non-normal incidence.
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