On the Origin of the Pluto System

Abstract

The goal of this chapter is to review hypotheses for the origin of the Pluto system in light of observational constraints that have been considerably refined over the 85-year interval between the discovery of Pluto and its exploration by spacecraft. We focus on the giant impact hypothesis currently understood as the likeliest origin for the Pluto-Charon binary, and devote particular attention to new models of planet formation and migration in the outer solar system. We discuss the origins conundrum posed by the system's four small moons. We also elaborate on implications of these scenarios for the dynamical environment of the early transneptunian disk, the likelihood of finding a Pluto collisional family, and the origin of other binary systems in the Kuiper belt. Finally, we highlight outstanding open issues regarding the origin of the Pluto system and suggest areas of future progress.

Large-scale cryovolcanic resurfacing on Pluto

“…Based on this rock abundance, Pluto is expected to have maintained relatively low levels of radiogenic heating (≲5 mW m −2 ) throughout much of its history 7,8 . Pluto's largest moon Charon (R = 606.0 ±1.0 km) likely formed through a large, grazing impact with Pluto 9,10 . Models predict the tidal evolution of Pluto and Charon progressed rapidly after the impact, and any tidal heating should have ended very early in their history (<100 Myrs after the impact) 11 .…”

Orbits and Masses of the Small Satellites of Pluto

“…However, even erosive impacts that did not deposit their dark material onto the small moons would lead to a darkening of their surfaces over time if material at depth within the moons exposed by the impacts was dark and rocky. Thus, the simplest explanation for how the tiny moons have maintained bright surfaces for billions of years is that their interiors are ice-rich like their surfaces (e.g., Weaver et al 2016;McKinnon et al 2017;Canup et al 2021).…”

“…Formation of an extended debris disk during a Charon-forming giant impact appears most likely when the colliding progenitor bodies are partially differentiated, with outer ice shells that overlay mixed icerock or hydrated rock interiors (Canup 2011). The partially differentiated structure implies outer ice melting during the end stages of progenitor accretion (Canup et al 2021) and that ice originating from the progenitor shells would have near-solid densities and not be highly porous. Ejection of intact fragments of such material into an extended debris disk might then lead to ice-rich but relatively low porosity small moons, in contrast to highly porous, ice-rich small KBOs envisioned to result from, e.g., gentle accretion via the streaming instability (Nesvorný et al 2019(Nesvorný et al , 2021, as seems required for formation of the fragile neck of Arrokoth (McKinnon et al 2020).…”

1I/‘Oumuamua as an N2 Ice Fragment of an Exo‐Pluto Surface II: Generation of N2 Ice Fragments and the Origin of ‘Oumuamua

“…Other models (Clement, Kaib, Raymond, & Walsh, 2018) suggest Neptune migrated perhaps closer to 10 Myr after the birth of the Solar System. Models overwhelmingly show that extensive oceans can form on Charon/Gonggong-sized bodies and Pluto-sized bodies on timescales < 100 Myr (Desch, Cook, Doggett, & Porter, 2009;Robuchon & Nimmo, 2011;Kimura & Kamata, 2020) (Canup, Kratter, & Neveu, 2020). According to the "hot early start" model for Pluto, it must have begun its geophysical evolution with a significant subsurface ocean (in < 10 5 years), or else the initial melting of ice to form the ocean would have manifested itself as compressional tectonic features on Pluto's surface (Bierson, et al, 2020).…”

“…Other models (Clement et al, 2018) suggest Neptune migrated perhaps closer to 10 Myr after the birth of the Solar System. Models overwhelmingly show that extensive oceans can form on Charon/Gonggong-sized bodies and Pluto-sized bodies on timescales <100 Myr (Desch et al, 2009;Kimura & Kamata, 2020;Robuchon & Nimmo, 2011) (Canup et al, 2020).…”