Distribution and Energy Balance of Pluto’s Nitrogen Ice, as seen by New Horizons in 2015
Briley Lewis, John Stansberry, Bryan Holler, William Grundy, Bernard Schmitt, Silvia Protopapa, Carey Lisse, S. Alan Stern, Leslie Young, Harold Weaver, Catherine Olkin, Kimberly Ennico, the New Horizons Science Team
(Submitted on 5 Dec 2019)
Pluto’s surface is geologically complex because of volatile ices that are mobile on seasonal and longer time scales. Here we analyzed New Horizons LEISA spectral data to globally map the nitrogen ice, including nitrogen with methane diluted in it. Our goal was to learn about the seasonal processes influencing ice redistribution, to calculate the globally averaged energy balance, and to place a lower limit on Pluto’s N2 inventory. We present the average latitudinal distribution of nitrogen and investigate the relationship between its distribution and topography on Pluto by using maps that include the shifted bands of methane in solid solution with nitrogen to more completely map the distribution of the nitrogen ice. We find that the global average bolometric albedo is 0.83 +\- 0.11, similar to that inferred for Triton, and that a significant fraction of Pluto’s N2 is stored in Sputnik Planitia. Under the assumption that Pluto’s nitrogen-dominated 11.5 microbar atmosphere is in vapor pressure equilibrium with the nitrogen ice, the ice temperature is 36.93 +/- 0.10 K, as measured by New Horizons. Combined with our global energy balance calculation, this implies that the average bolometric emissivity of Pluto’s nitrogen ice is probably in the range 0.47 – 0.72. This is consistent with the low emissivities estimated for Triton based on Voyager, and may have implications for Pluto’s atmospheric seasonal variations, as discussed below. The global pattern of volatile transport at the time of the encounter was from north to south, and the transition between condensation and sublimation within Sputnik Planitia is correlated with changes in the grain size and CH4 concentration derived from the spectral maps. The low emissivity of Pluto’s N2 ice suggests that Pluto’s atmosphere may undergo an extended period of constant pressure even as Pluto recedes from the Sun in its orbit.
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1912.02333 [astro-ph.EP] (or arXiv:1912.02333v1 [astro-ph.EP] for this version)
Submission history
From: Briley Lewis
[v1] Thu, 5 Dec 2019 01:25:55 UTC (17,811 KB)
