Pluto's Sputnik basin as a peak-ring or multiring basin: A comparative study

Pluto's Sputnik basin is the only large impact basin in the outer Solar System that resembles basins in the inner Solar System in morphology and scale, with dimensions of -1800 x 1000 km and a depth of -2.5 km. Sputnik basin has been compared to giant impact basins without prominent topographic rings, such as the Hellas basin on Mars and South Pole-Aitken basin on the Moon. However, a north-south trending arcuate chain of water-ice mountain blocks within the western half of the basin resembles a peak-ring structure as found in impact basins on terrestrial bodies, suggesting that Sputnik basin may be more analogous to a peak-ring or multiring basin. Here, we perform a comparative analysis between Sputnik basin and 23 impact basins in the inner Solar System. We reconstruct Sputnik basin's topography prior to being partially filled with an N2-rich ice deposit. In our analyses, we measure key characteristics such as average radial topography, ring spacing and crustal/shell thinning beneath the basins. We find that Sputnik basin is morphologically, topographically, and structurally consistent with the peak-/multiring basins, having most similarities to Apollo and Humboldtianum basins on the Moon, rather than giant impact basins without prominent topographic rings. Sputnik's consistency with a peak-/multiring structure has implications for aspects of its formation, evolution, and structure. In particular, this new interpretation of the basin structure decreases the size of both the impactor and the possible mass anomaly contained within the basin by half relative to previous interpretations.