  Observations of Pluto's surface made by the New Horizons spacecraft indicates
present-day nitrogen ice glaciation in and around the basin known as Sputnik
Planum. Motivated by these observations, we have developed an evolutionary
glacial flow model of solid nitrogen ice taking into account its published
thermophysical and rheologies properties. This model assumes that glacial ice
layers flow laminarly and have low aspect ratios which permits a vertically
integrated mathematical formulation. We assess the conditions for the validity
of laminar nitrogen ice motion by revisiting the problem of the onset of
solid-state buoyant convection of nitrogen ice for a variety of bottom thermal
boundary conditions. Subject to uncertainties in nitrogen ice rheology,
nitrogen ice layers are estimated to flow laminarly for thicknesses less than
400-1000 meters. The resulting mass-flux formulation for when the nitrogen ice
flows as a laminar dry glacier is characterized by an Arrhenius-Glen functional
form. The flow model developed is used here to qualitatively answer some
questions motivated by observed glacial flow features found on Sputnik Planum.
We find that the wavy transverse dark features found along the northern
shoreline of Sputnik Planum may be a transitory imprint of shallow topography
just beneath the ice surface suggesting the possibility that a major shoreward
flow event happened relatively recently within the last few hundred years.
Model results also support the interpretation that the prominent darkened
features resembling flow lobes observed along the eastern shoreline of the
Sputnik Planum basin may be a result of wet nitrogen glacial ice flowing into
the basin from the pitted highlands of eastern Tombaugh Regio.
