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Project Progress

Trans-Neptunian Objects (TNOs) contain some of the most pristine material in the solar system and therefore offer a unique opportunity to study chemical and physical properties of the early solar system. Approximately 10 of TNOs show unusually blue/neutral spectral slopes, a trait which is likely attributable to resurfacing from either collision events or cometary-like outgassing. A collisional group of objects in the Kuiper belt, the Haumea family show blue colors and water-ice absorption features in their spectra. Searching for rotational variation in color of these TNOs is a powerful diagnostic for three reasons: (1) presence or lack of color variation helps discern between these two resurfacing theories; (2) knowledge of the rotation period will help us constrain the density and structure of these objects; and (3) if color variation due to a collision event is detected, we can infer an outer solar system collision history that constrains solar system dynamical formation models. Determining shapes of TNO solar phase curves offers another powerful technique for probing TNO surfaces which, when combined with Hapke solar scattering models, constrain texture, grain size, albedo, porosity, and complex refractive index of the optically active surfaces. Knowledge of these key properties has already significantly influenced dynamical models of solar system formation and ongoing evolution. Despite the potential of this type of observation to constrain models and reveal otherwise elusive physical properties, only 7 blue/neutral TNO phase curves are known. Furthermore, although previous studies suggest a color-phase curve and a dynamical class-phase curve correlation, existing phase curve data cover a poor range of dynamical classes, phase angles, and colors (particularly in the blue/neutral end).

The search for color variation and phase curves in a sample of blue/neutral TNOs has begun and this forms the PhD thesis for one of our team’s graduate students (S. Sonnett). Phase one of this campaign involved identifying survey members with detectable brightness variation, and this phase was completed in December 2009. Phase two is follow-up observations of those TNOs flagged as variant. Over the past year, we have completed phase one, finding detectable variation in 73% of our targets, and begun phase two. Phase two is currently 45% complete, with completion anticipated during Spring 2011.