Drs. Shepard and Clark will conduct a multi-wavelength observational campaign of about 25 X/M/E class asteroids using the Arecibo planetary radar and NASA Infrared Telescope Facilities. The research objectives are to (1) physically characterize the M and E asteroids, (2) search for the metallic cores of disrupted parent bodies, and (3) look for relationships between the asteroids radar properties, size, and spectral properties. The goals are to resolve the compositional ambiguities of these important asteroid classes and answer outstanding questions about solar system formation. Undergraduate students will be involved in all phases of this work.
This research team has maximized their observing opportunities for the next three years. They will make the following near-simultaneous observations of each target: (1) 12.6cm radar imaging (Arecibo), (2) Near Infrared observations. The observations are designed to address the following questions: (1) What fraction of the M-class asteroids are metal-rich? Radar is especially sensitive to metallic compositions, making it a unique tool for differentiating between metal-rich and metal-poor asteroids. (2) Is there a size difference in the metal-rich versus metal-poor M-class population? Observations suggest M-class asteroids >75 km in size are more likely to show evidence of hydration, while those <75 km show no evidence of hydration. Other studies suggest that metal cores of disrupted asteroids are likely <60 km in size. Roughly half of this teams targets are larger than 75 km, allowing this question to be addressed statistically. (3) Are there correlations between the radar and spectral properties of M-class asteroids? The goal is to find spectral features that may correlate with radar evidence of a metal-rich or metalpoor composition. (4) How common are large variations in radar albedo among M-class asteroids and what are the causes? Previous work has detected this behavior in 129 Antigone and 785 Zwetana. What is the cause of this variability? How many M-asteroids display this behavior? (5) What are the physical properties of the E-class asteroids? The survey includes three E-class asteroids including the 44 Nysa and 434 Hungaria. Only one E-type has ever been observed by radar, 3103 Eger.
The broader impacts of this work can be summarized as follows. A survey and physical characterization of the X/M/E main-belt asteroid population provides society with information that will be of use to: (1) Estimate the statistical population of metallic asteroids, arguably the most serious impact threat to the Earth, and (2) Evaluate the potential metal and water resources available in the MBA population. These researchers will involve undergraduates in all phases of this work and hope to attract strong students into the astronomical sciences. ***
