BOLOMETRIC HEMISPHERICAL ALBEDO MAP OF PLUTO

The New Horizons spacecraft flyby of Pluto in 2015 revealed an extremely variable surface with expansive dark, bright, and intermediate terrains, abundant volatile and refractory ices, and complex geology from endogenous and exogenous processes (e.g., Stern et al., 2015). Pluto is an active world with ongoing convective and glacial resurfacing, seasonal volatile transport, and radiation processing (e.g., Gladstone et al., 2016; Grundy et al., 2016; Moore et al., 2016). Bolometric hemispherical albedo is the flux-weighted, wavelength-integrated ratio of total power scattered by a surface to incident power, where total refers to integration over all scattering angles; it is the energy balance albedo, equal to one minus absorption. We present and geologically interpret a bolometric hemispherical albedo map of Pluto from New Horizons observations. Pluto exhibits extraordinarily large and sharp albedo variations with location, among the largest in the solar system (e.g., Buratti et al., 2017). Pluto’s ~1000 km diameter, mid-latitude, nitrogen-ice sheet is among its highest albedo terrains. To its immediate southwest, an ~3000 by 500 km region that stretches over ~150 degrees in longitude, is among the darkest terrains. Evidently, processes operating on Pluto can effectively sort dark and bright material. Pluto’s exceptionally bright terrains are also very young, as evidenced by few-to-no impact craters. This suggests that deposition of dark material is inhibited on Pluto’s brightest terrains or it is rapidly sequestered. We also find that albedos on Pluto are generally dominated by three regimes. Strong correlations between topography and albedo are discussed, along with some intriguing exceptions. Pluto’s albedos and corresponding geologic units, both dark and bright, are compared to that of other distant small bodies (e.g., Hofgartner et al., 2019; 2021). Albedo is a useful measurement that constrains volatile transport by quantifying the absorbed solar energy as well as providing insight into interior-surface-atmosphere processes.