The vast, deep, volatile-ice-filled basin informally named Sputnik Planum is central to Pluto's geological activity 1,2 . Composed of molecular nitrogen, methane, and carbon monoxide ices 3 , but dominated by N2-ice, this ice layer is organized into cells or polygons, typically ~10-40 km across, that resemble the surface manifestation of solid state convection 1,2 . Here we report, based on available rheological measurements 4 , that solid layers of N2 ice ≳1 km thick should convect for estimated present-day heat flow conditions on Pluto. More importantly, we show numerically