Distribution and Energy Balance of Pluto’s Nitrogen Ice, as seen by New Horizons in 2015. (arXiv:1912.02333v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lewis_B/0/1/0/all/0/1">Briley Lewis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stansberry_J/0/1/0/all/0/1">John Stansberry</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Holler_B/0/1/0/all/0/1">Bryan Holler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Grundy_W/0/1/0/all/0/1">William Grundy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schmitt_B/0/1/0/all/0/1">Bernard Schmitt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Protopapa_S/0/1/0/all/0/1">Silvia Protopapa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lisse_C/0/1/0/all/0/1">Carey Lisse</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stern_S/0/1/0/all/0/1">S. Alan Stern</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Young_L/0/1/0/all/0/1">Leslie Young</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Weaver_H/0/1/0/all/0/1">Harold Weaver</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Olkin_C/0/1/0/all/0/1">Catherine Olkin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ennico_K/0/1/0/all/0/1">Kimberly Ennico</a>, the <a href="http://arxiv.org/find/astro-ph/1/au:+Team_New_Horizons_Science/0/1/0/all/0/1">New Horizons Science Team</a>

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.

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.

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