Sputnik Planitia likely originated as an impact basin that subsequently collected volatile ices. The size of the hypothetical impactor has been estimated as 150–300 km. 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. The accumulation of several kilometers of nitrogen ice in the basin was in part a consequence of its higher surface pressure, which leads to a higher N2 condensation temperature. The positive temperature gradient of Pluto's atmosphere contributes to making a topographic depression a cold trap.
