Pluto's haze as a surface material

Abstract

Pluto's atmospheric haze settles out rapidly compared with geological timescales. It needs to be accounted for as a surface material, distinct from Pluto's icy bedrock and from the volatile ices that migrate via sublimation and condensation on seasonal timescales. This paper explores how a steady supply of atmospheric haze might affect three distinct provinces on Pluto. We pose the question of why they each look so different from one another if the same haze material is settling out onto all of them. Cthulhu is a more ancient region with comparatively little presentday geological activity, where the haze appears to simply accumulate over time. Sputnik Planitia is a very active region where glacial convection, as well as sublimation and condensation rapidly refresh the surface, hiding recently deposited haze from view. Lowell Regio is a region of intermediate age featuring very distinct coloration from the rest of Pluto. Using a simple model haze particle as a colorant, we are not able to match the colors in both Lowell Regio and Cthulhu. To account for their distinct colors, we propose that after arrival at Pluto's surface, haze particles may be less inert than might be supposed from the low surface temperatures. They must either interact with local materials and environments to produce distinct products in different regions, or else the supply of haze must be non-uniform in time and/or location, such that different products are delivered to different places.

Cryovolcanic flooding in Viking Terra on Pluto

“…Attention was initially drawn to Virgil Fossae by the nearly unique color both in the main trough and in the immediate surroundings, a color having only a few smaller exposures (e.g., Beatrice Fossae) on the hemisphere of Pluto imaged with high resolution by New Horizons (Olkin et al 2017). The varied and widespread coloration of Pluto's ices is attributed to refractory complex organic compounds (tholins) formed by photochemical reactions in the atmosphere and precipitated to the surface (Cheng et al 2017;Grundy et al 2018), and more directly by photolysis and radiolysis of CH 4 and N 2 in the surface ices (e.g., Cruikshank et al 2016). In view of the special colors in Virgil Fossae, Cruikshank et al (2019b) proposed that complex organics present in a subsurface fluid reservoir that supplied the cryolava in the fossa trough and surroundings by cryoclastic eruptions constitute a third source of tholins now seen on the planet's surface.…”

Kuiper Belt object 2014MU69, Pluto and Phoebe as windows on the composition of the early solar nebula

“…Pluto's surface shows solid N 2 , CH 4 , CO, H 2 O, NH 3 ices, plus colored refractory organics from photolysis/radiolysis of surface ices (Materese et al 2014(Materese et al , 2015Baratta et al 2015;Grundy et al 2018). The surface deposits of non-ice components that are varied in color, but primarily red-brown, are interpreted as a refractory polymer-like organic complex (termed tholin) made by the energetic processing of hydrocarbons and other molecules in the surface ices and the atmosphere.…”

Simulated effect of the Galactic Cosmic Rays on the surface of Pluto’s dark-red region

“…On Pluto, the largest object in the Kuiper Belt, the dark surface of Cthulhu seems to indicate the presence of photochemical aerosols, stemming from the interaction between solar ultraviolet radiation and atmospheric methane, nitrogen, carbon monoxide, and further sedimentation [1][2][3][4]. Tholins have been tested and identified as analogues of the said surface.…”