Sputnik Planitia

Sputnik Planitia was first resolved in July 2015 during the New Horizons flyby, which revealed Pluto's surface in unprecedented detail. The informal name, approved by the International Astronomical Union in 2017, honors Sputnik 1, the first artificial satellite, reflecting the Soviet Union's pioneering role in space exploration. The feature lies within Tombaugh Regio, named after Pluto's discoverer Clyde Tombaugh. Its name was chosen through the Our Pluto campaign, a public engagement initiative that allowed people to suggest names for surface features.

Sputnik Planitia is composed primarily of nitrogen ice, with smaller amounts of methane and carbon monoxide ices. The plain is remarkably smooth and crater-free, indicating a surface age of less than 10 million years, a blink in geologic time. It is divided into polygonal cells, typically 10–40 km across, that are thought to result from solid-state convection within the nitrogen ice, driven by heat from Pluto's interior. The ice is several kilometers thick, and the basin is about 3.5 km deep relative to the surrounding terrain, suggesting a large impact origin or a downwelling caused by the weight of the ice.

The plain exhibits active glacial processes, including the flow of nitrogen ice from the eastern highlands into the basin, forming valley glaciers and lobate flow features. At its margins, Sputnik Planitia interacts with water-ice mountains, such as the Wright Mons and Piccard Mons, which may be cryovolcanoes. The surface temperature is about 38 K (−235 °C), near the freezing point of nitrogen, so the ice is in a state of sublimation and condensation that drives a nitrogen cycle. This cycle, analogous to Earth's water cycle, produces seasonal frosts and may drive winds that create dark streaks on the plain.

One of the most intriguing aspects of Sputnik Planitia is its possible relationship with a subsurface ocean. The plain's location near Pluto's anti-Charon point and its positive gravity anomaly suggest that the basin may have formed as a result of an impact that created a mascon, and that a subsurface ocean may exist beneath the ice shell, causing the basin to reorient over time. Additionally, the polygonal cells are thought to be sites of upwelling and downwelling, with the surface showing evidence of recent resurfacing. The plain also hosts 'pits' that may be formed by sublimation, and its nitrogen ice is so soft that it behaves like a fluid on geologic timescales, creating a dynamic landscape that is unique in the Solar System.

Tombaugh Regio

The large, bright heart-shaped region on Pluto, of which Sputnik Planitia forms the western lobe.

New Horizons

NASA spacecraft that performed the first flyby of Pluto in 2015.

Nitrogen ice

Solid nitrogen, the primary constituent of Sputnik Planitia's surface.

Solid-state convection

Slow convective motion in a solid that behaves plastically over long timescales.

Mascon

A region of high gravitational acceleration caused by a concentration of dense material.