Calibration Of Calcic Pyroxenes For Interpreting Meteorite And Asteroid Spectra

Calcic pyroxenes are a group of silicate minerals that are found in meteorite and asteroid spectra. I investigated the relationship of high-calcium clinopyroxenes in comparison with orthopyroxenes, pigeonites, mixtures, and the meteorite group of angrites to try to find any trends for spectral calibrations. I used spectra from HOSERLab, RELAB, and the USGS Spectral Library. The main band minima of pyroxenes in spectra are around 0.9 or 1 µm for band I and 1.15 or 2 µm for band II, with the former minima for type A clinopyroxenes and the latter for type B. Using sample minima found from both lowest reflectances and polynomial fittings, I graphed the different pyroxene features to view possible trends from band positions and calcium, iron, and magnesium abundances. The type B clinopyroxenes continued on previous trends found in the literature, having a stronger band position relationship for the iron and calcium contents than the type A clinopyroxene samples. However, their band position relationships with iron and calcium were much less linear than the orthopyroxenes, which has also been seen previously in the literature. The two main band minima found from the different methods were similar in band position for band I, while due to noise and slope, the band II features were more diverse. I also examined how calcic clinopyroxenes interacted in comparison to other minerals in mixtures. There did not appear to be a trend for the type A clinopyroxenes, although it was also complicated by the larger error in band positions from reddened slopes and faintness. When in mixtures with orthopyroxene and/or olivine there needed to be a large amount, usually around ≥ 70 % calcic pyroxene, before the minima could be found. Angrite spectra were also looked at because they typically have a large amount of calcic clinopyroxene, including type A, although usually with larger amounts of titanium and aluminum. There were limited samples so I was unable to find any trends from them, but I investigated a set of mixtures from Cloutis et al. (2006a) and a set made for this study from HOSERLab that were made to resemble possible angrite and angrite parent-body spectra. From these, more data were available to show how a combined 1 µm feature from type A high-calcium pyroxene and olivine changes with differing amounts of both

Basalt or Not? Near-infrared Spectra, Surface Mineralogical Estimates, and Meteorite Analogs for 33 V-p-type Asteroids

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 mu m) reflectance spectra, surface mineralogical characterizations, analysis of spectral band parameters, and meteorite analogs for 33 V-p 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 similar to 0.9 and similar to 1.9 mu m. Combined with the results from Hardersen et al., we identify basaltic asteroids for similar to 95% (39/41) of our inner-belt Vp sample, but only similar to 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 V-p 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.NASA Planetary Astronomy Program Grant [NNX14AJ37G]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]