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What is Sputnik Planitia?
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Pluto
Pluto as observed by the New Horizons spacecraft, July 13, 2015.
Sputnik Planitia is a smooth, craterless plain of nitrogen ice located on the western half of the heart-shaped Tombaugh Regio on Pluto. Its lack of impact craters indicates that it is a geologically young feature, suggesting that the dwarf planet remains geologically active.1
The region is a deep basin that may have been formed by an impact. It is situated on Pluto’s tidal axis, directly opposite the moon Charon. Because of its specific location, scientists believe there must be extra mass beneath the surface of Sputnik Planitia, which may be evidence of a subsurface ocean located between Pluto's rocky core and its outer mantle of water ice.1