Using rotation and polarization to probe the composition and surface properties of Main Belt asteroids

2009 • 2009PhDT........35M

Authors • Masiero, Joseph R.

Abstract • Ground-based observations of small Solar System bodies provide a wealth of data on their physical properties. Using imaging observations from the Canada- France-Hawaii Telescope and both imaging and polarimetry from the University of Hawaii's 2.2 m telescope I have analyzed light curve and polarimetry measurements for Main Belt asteroids to characterize their physical properties. The debiased spin rate distribution of asteroids shows evidence for non- collisional evolution for objects with diameters of 500 m < D < 10 km, attributable to YORP alteration of spin rates. The debiased light curve amplitude distribution shows evidence for two populations with independent shape distributions, indicative of two different pathways of formation history. High precision asteroid polarization studies required new instrumentation to be developed for the UH 2.2 m telescope. I designed, constructed and calibrated a new imaging polarimeter able to reach 0.1% polarization accuracy for point sources of V < 17 mag. Using observations of the Main Belt asteroid (387) Aquitania I confirm the correlation between spinel features in an asteroid's IR spectrum and the unique polarization-phase curve observed for large inversion angle objects. Asteroid polarization is a strong function of the surface particle spacing and measurements of the polarization-phase curve can give us a unique window into the mineralogical composition of the surface. I have developed theoretical models that show the size of the dust on an asteroid's surface has no effect on its polarization, which is instead dependent solely on mineralogy. Finally, I have found albedo variations across the surface of a small ( D = 2.3 km) near-Earth asteroid resulting from a dark area covering ~2% of the asteroid's surface, likely due to an impact crater from a low albedo impactor. Through both rotation and polarization studies I have extended our understanding of the physical properties of asteroids.

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