Browsing UA Faculty Publications by Subjects
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OSIRIS‐REx Visible and Near‐Infrared Observations of the MoonThe Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission observed the Moon during the spacecraft's Earth gravity assist in 2017. From the spacecraft view, the lunar phase was 42 degrees, and the in-view hemisphere was dominated by anorthositic highlands terrain. Lunar spectra obtained by the OSIRIS-REx Visible and InfraRed Spectrometer show evidence of several candidate absorption features. We observe the 2.8-mu m hydration band, confirming the spectral results from other missions, but detected in full-disk spectra. We also tentatively identify weak spectral features near 0.9 and 1.3 mu m, consistent with lunar regolith containing a mixture of plagioclase and orthopyroxene minerals, as expected for highlands terrain.
Spectral clustering tools applied to Ceres in preparation for OSIRIS-REx color imaging of asteroid (101955) BennuThe OSIRIS-REx asteroid sample-return mission is investigating primitive near-Earth asteroid (101955) Bennu. Thousands of images will be acquired by the MapCam instrument onboard the spacecraft, an imager with four color filters based on the Eight-Color Asteroid Survey (ECAS): b' (473 nm), v (550 nm), w (698 nm), and x (847 nm). This set of filters will allow identification and characterization of the absorption band centered at 700 nm and associated with hydrated silicates. In this work, we present and validate a spectral clustering methodology for application to the upcoming MapCam images of the surface of Bennu. Our procedure starts with the projection, calibration, and photometric correction of the images. In a second step, we apply a K-means algorithm and we use the Elbow criterion to identify natural clusters. This methodology allows us to find distinct areas with spectral similarities, which are characterized by parameters such as the spectral slope S' and the center and depth of the 700-nm absorption band, if present. We validate this methodology using images of (1) Ceres from NASA's Dawn mission. In particular, we analyze the Occator crater and Ahuna Mons. We identify one spectral cluster located in the outer parts of the Occator crater interior showing the 700-nm hydration band centered at 698 +/- 7 nm and with a depth of 3.4 +/- 1.0%. We interpret this finding in the context of the crater's near-surface geology.
Thermal alteration of labile elements in carbonaceous chondritesCarbonaceous chondrite meteorites are some of the oldest Solar System planetary materials available for study. The CI group has bulk abundances of elements similar to those of the solar photosphere. Of particular interest in carbonaceous chondrite compositions are labile elements, which vaporize and mobilize efficiently during post-accretionary parent-body heating events. Thus, they can record low-temperature alteration events throughout asteroid evolution. However, the precise nature of labile-element mobilization in planetary materials is unknown. Here we characterize the thermally induced movements of the labile elements S, As, Se, Te, Cd, Sb, and Hg in carbonaceous chondrites by conducting experimental simulations of volatile-element mobilization during thermal metamorphism. This process results in appreciable loss of some elements at temperatures as low as 500 K. This work builds on previous laboratory heating experiments on primitive meteorites and shows the sensitivity of chondrite compositions to excursions in temperature. Elements such as S and Hg have the most active response to temperature across different meteorite groups. Labile element mobilization in primitive meteorites is essential for quantifying elemental fractionation that occurred on asteroids early in Solar System history. This work is relevant to maintaining a pristine sample from asteroid (101955) Bennu from the OSIRIS-REx mission and constraining the past orbital history of Bennu. Additionally, we discuss thermal effects on surface processes of near-Earth asteroids, including the thermal history of “rock comets” such as (3200) Phaethon. This work is also critical for constraining the concentrations of contaminants in vaporized water extracted from asteroid regolith as part of future in situ resource utilization for sustained robotic and human space exploration.