About 1,400 by 1,200 km (870 by 750 mi) in size,[3] Sputnik Planitia is partially submerged in large, bright glaciers of nitrogen ice.

Much of it has a surface of irregular polygons separated by troughs, interpreted as convection cells in the relatively soft nitrogen ice.

[10] Near the northwest margin is a field of transverse dunes (perpendicular to the windstreaks), spaced about 0.4 to 1 km apart, that are thought to be composed of 200-300 μm diameter particles of methane ice derived from the nearby Al-Idrisi Montes.

[1] Alternatively, it has been suggested that the accumulation of ices in this location depressed the surface there, leading to the formation of a basin via a positive feedback process without an impact.

[16] The positive temperature gradient of Pluto's atmosphere contributes to making a topographic depression a cold trap.

A high seasonal thermal inertia of Pluto's surface is an important driver of deposition of nitrogen ice at low latitudes.

Simulations suggest that over a period of about a million years, the runaway process would collect much of the ice into a single cap even in the absence of a preexisting basin.

[22] The accumulation of dense nitrogen ice would have contributed to making Sputnik Planitia a positive gravity anomaly, but by itself would not have been sufficient to overcome the topographic depression associated with the basin.

[23] Gradual freezing of such an ocean, in combination with polar wander and the loading of Sputnik Planitia with ice, would also explain the extensional tectonic features seen across Pluto.

A similar mechanism may contribute to the formation of subsurface oceans on other outer Solar System satellites and trans-Neptunian objects.

[26][27] Modeling of nitrogen ice convection cells suggests a depth of about one tenth their width, or 3–4 km for most of the planitia, and a maximum flow rate of about 7 cm per year.

[32] Some groups of hills in the basin are named after spacecraft; for example, “Coleta de Dados”, in honor of the first Brazilian satellite launched into space.

[33] Immediately to the southwest of the Tenzing Montes (context) is a large, circular mountain with a central depression, Wright Mons.