Geophysical Evolution of Sputnik Basin on Pluto

Abstract

The past and present subsurface structure of icy outer Solar System worlds, such as Pluto, provides insight into their formation and interior evolution. Placing constraints on the structure of planetary interiors has been one of the primary challenges in the field of Solar System science. NASA’s New Horizons mission flyby of Pluto in 2015 revealed its surface in high resolution for the first time but did not gather any spatially resolved gravitational data. Consequently, Pluto’s interior is still mostly unknown. Sputnik basin, an ~2000 × 1000 km elongated impact basin in Pluto’s equatorial region observed on the encounter hemisphere, has played an integral role in shedding light on Pluto’s interior. In this thesis, I present new interpretations of Sputnik basin’s structure and support, proposing an evolutionary pathway for the basin with implications for Pluto’s past and present interior structure.This dissertation analyzes Sputnik basin through a set of multi-faceted techniques, including structural characterization of the basin, geoid and thermal modeling, to present a seamless story of the basin’s evolution. My investigations in Chapter 2 revealed that Sputnik basin is consistent with peak-/multiring basins in the inner Solar System, implying a decrease in any subsurface uplift by ~ 40%. A proposed peak-ring structure redefines the impactor diameter, impact angle, and subsequent impact basin evolution. In Chapter 3, I use a novel approach assuming the low-viscosity deposit within the basin conforms to Pluto’s geoid and calculate the gravity field over the basin considering both giant impact and peak-ring structures. Sputnik basin is most likely uncompensated and a mass deficit today. Here, I first propose that Sputnik basin may have transitioned from a past mass excess or overcompensated state to a present-day mass deficit through refreezing of the uplifted subsurface ocean beneath the basin. In Chapter 4, I utilize thermal modeling to show that this process can result in transitioning the basin’s mass anomaly to a current mass deficit. Inclusion of insulating layers and properties does not affect our results despite their influence on the refreezing timescale of the Pluto’s ice shell. These findings contribute to our understanding of Sputnik basin’s geophysical evolution, demonstrating the importance of large impact basin studies on data-limited icy outer Solar System worlds like Pluto.