Pluto’s smooth surface is probably a sea of slow-flowing nitrogen ice

http://www.extremetech.com/wp-content/uploads/2016/06/pluto-surface-768x424.jpg 768w, http://www.extremetech.com/wp-content/uploads/2016/06/pluto-surface-640x353.jpg 640w, http://www.extremetech.com/wp-content/uploads/2016/06/pluto-surface-672x371.jpg 672w, http://www.extremetech.com/wp-content/uploads/2016/06/pluto-surface.jpg 1344w" sizes="(max-width: 300px) 100vw, 300px" />Pluto’s Sputnik Planum region can remake itself to erase impact craters thanks to nitrogen ice and radioactive elements.