New Horizons disk-integrated approach photometry of Pluto and Charon

Approach and cruise observations of Pluto and Charon by NASA's New Horizons LOng Range Reconnaissance Imager ("LORRI") allow monitoring of Pluto not only at phase angles beyond Earth's 2 degree limit, but present a near constant sub-observer latitude of 43 degrees. However, the creation of light curves and solar phase curves of the pair prove to be an interesting challenge. Early images of the pair from July 2013 are barely resolved and have low signal, while later images show the pair clearly resolved and at sufficient resolution. Just at the Pluto approaches the signal level and image quality of prior HST images, surface features become resolved, rendering disk integrated photometry increasingly difficult and inaccurate, with the largest discrepancies found at longitudes which show the intersection of features informally named Tombaugh Regio ("the heart") and Cthulhu Macula ("the whale"). Now, post flyby, accurate knowledge of the radius and the shapes of surface features and their patterns of dark and light, allow for the creation of custom PSFs created from flyby maps. Using these maps, we present disk-integrated approach photometry, a solar phase curve and estimate Hapke parameters, taking into account the sub-observer position.This work was supported by the NASA New Horizons Project.