Disk-resolved Photometric Properties of Pluto and the Coloring Materials across its Surface

• Published in: The Astronomical Journal
• Main Authors: Protopapa, Silvia, Olkin, Cathy B., Grundy, Will M., Li, Jian-Yang, Verbiscer, Anne, Cruikshank, Dale P., Gautier, Thomas, Quirico, Eric, Cook, Jason C., Reuter, Dennis, Howett, Carly J. A., Stern, Alan, Beyer, Ross A., Porter, Simon, Young, Leslie A., Weaver, Hal A., Ennico, Kim, Dalle Ore, Cristina M., Scipioni, Francesca, Singer, Kelsi
• Other Authors: Southwest Research Institute Boulder (SwRI), Lowell Observatory Flagstaff, Planetary Science Institute Tucson (PSI), University of Virginia, NASA Ames Research Center (ARC), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Pinhead Institute, Smithsonian Institution, NASA Goddard Space Flight Center (GSFC), Search for Extraterrestrial Intelligence Institute (SETI), Johns Hopkins University Applied Physics Laboratory Laurel, MD (APL)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDU]Sciences of the Universe [physics]; North Pole; Sputnik
• Online Access: https://insu.hal.science/insu-02468367; https://doi.org/10.3847/1538-3881/ab5e82

International audience A multiwavelength regionally dependent photometric analysis of Pluto's anti-Charon-facing hemisphere using images collected by New Horizons' Multispectral Visible Imaging Camera (MVIC) reveals large variations in the absolute value and spectral slope of the single-scattering albedo. Four regions of interest are analyzed: the dark equatorial belt, Pluto's north pole, nitrogen-rich regions, and the mid-latitude terrains. Regions dominated by volatile ices such as Lowell Regio and Sputnik Planitia present single-scattering albedos of ~0.98 at 492 nm, almost neutral across MVIC's visible wavelength range (400–910 nm), indicating limited contributions from tholin materials. Pluto's dark equatorial regions, informally named Cthulhu and Krun Maculae, have single-scattering albedos of ~0.16 at 492 nm and are the reddest regions. Applying the Hapke radiative transfer model to combined MVIC and Linear Etalon Imaging Spectral Array (LEISA) spectra (400–2500 nm) of Cthulhu Macula and Lowell Regio successfully reproduces the spectral properties of these two regions of dramatically disparate coloration, composition, and morphology. Since this model uses only a single coloring agent, very similar to the Titan-like tholin of Khare et al., to account for all of Pluto's colors, this result supports the Grundy et al. conclusion that Pluto's coloration is the result of photochemical products mostly produced in the atmosphere. Although cosmic rays and extreme ultraviolet photons reach Pluto's surface where they can drive chemical processing, observations of diverse surface colors do not require different chemical products produced in different environments. We report a correction scaling factor in the LEISA radiometric calibration of 0.74 ± 0.05.