Surface Spectroscopy Center of Excellence

The New Horizons Mission plans to flyby a Kuiper Belt Object (KBO) after the flyby of Pluto. The analyses of the surface composition of a KBO requires modeling of spectral information derived from scattered light measurements. Models for KBO surfaces in scattered light can be improved by the RRT approach in the regime where the particle size on the surface is similar to the wavelength. A future mission to a trojan asteroid is prioritized by the National Academy of Science New Worlds New Horizons 2011 decadal report. Robotic missions to asteroids also are in the NASA Global Exploration Roadmap. Interpreting spectroscopy of Trojan Asteroids, Centaurs, and Kuiper Belt Objects, for example, sets the stage for analyzing the surfaces of outer bodies that probe the formation and evolution scenarios for these primitive bodies. Outer bodies often appear to have surfaces with dark red materials or with crystalline silicates, and these components of their surface compositions may be a product of surface evolution or of the collection of debris from collisions of other bodies. Standard models can be tuned to fit spectra of Trojan asteroid surfaces by embedding crystalline silicates in a optically transparent matrix (Emery et al. 2006, Icarus 182, 496) or by assuming that top mm-thickness of the surface is so highly porous that the grains in this layer are assumed to be emitting at a single temperature (Vernazza et al. 2012, Icarus 221, 1162). The RRT models allow for an improved sophistication over assuming a transparent medium or a single temperature in the near-surface layers. Drawing a more intricate picture with RRT of how the structure and composition of the surface allows for the wavelength-dependent penetration and reflection of sunlight, as well as emission of thermal radiation, will deepen our understanding of the origins and evolution of these solar system bodies. Further advances in RRT require revision of radiative transfer models so that these models can propagate the amplitude and phase dependence of light passing through thin layers as the thin layers compromise the regolith/surface. The publicly available DISORT model is found inadequate to the task; a model with Ames' heritage by J. Pollack is the next avenue for approach. Regolith Radiative Transfer may be fundable through SMD Planetary Division under the Solar System Workings or Emerging Worlds (Cuzzi as PI, Wooden, Vahidinia as Co-Is), and to NSF (Vahidinia as PI). The National Science Foundation has a Astronomy and Astrophysics Research Grants (AAG) program that supports studies of the detailed characterization, structure and composition of the surfaces and the nature of small bodies (asteroids, comets, and Kuiper-belt objects).