The wide-binary origin of the Pluto–Charon system

Abstract

The Pluto-Charon binary system is the best-studied representative of the binary Kuiper-belt population. Its origins are vital to understanding the formation of other Kupier-belt objects (KBO) and binaries, and the evolution of the outer solar-system. The Pluto-Charon system is believed to form following a giant impact between two massive KBOs at relatively low velocities. However, the likelihood of a random direct collision between two of the most massive KBOs is low, and is further constrained by the requirement of a low-velocity collision, making this a potentially fine-tuned scenario. Here we expand our previous studies and suggest that the proto-Pluto-Charon system was formed as a highly inclined wide-binary, which was then driven through secular/quasi-secular evolution into a direct impact. Since wide-binaries are ubiquitous in the Kuiper-belt with many expected to be highly inclined, our scenario is expected to be robust. We use analytic tools and few-body simulations of the triple Sun-(proto-)Pluto-Charon system to show that a large parameter-space of initial conditions leads to such collisions. The velocity of such an impact is the escape velocity of a bound system, which naturally explains the low-velocity impact. The dynamical evolution and the origins of the Pluto-Charon system could therefore be traced to similar secular origins as those of other binaries and contact-binaries (e.g. Arrokoth), and suggest they play a key role in the evolution of KBOs.

A Pluto--Charon Concerto II. Formation of a Circumbinary Disk of Debris After the Giant Impact

“…The lower mass secondary loses momentum and is captured by the more massive primary; debris from the collision orbits the newly-formed, compact binary. In a more recent option, the planets first form a very wide binary (Rozner et al 2020). Over time, the orbit decays, which facilitates a collision with a geometry similar to that in a giant impact.…”

Chaotic dynamics of wide triples induced by galactic tides: a novel channel for producing compact binaries, mergers, and collisions

“…while Grishin et al (2018b) obtained analytical modified expressions for 𝑒 max and the critical inclination for ZLK resonance. The astrophysical implications of the correction for double-averaging are also relevant for evection resonances and stability of irregular satellites (Grishin et al 2017), formation of contact binaries in the Kuiper belt (Grishin et al 2020;Rozner et al 2020), Hot Jupiters and gravitational wave mergers of binary black holes Antonini & Perets (2012); Liu & Lai (2018); Grishin et al (2018b); Fragione et al (2019) and type Ia supernovae (Katz & Dong 2012;Haim & Katz 2018;Toonen et al 2018).…”

Binaries are softer than they seem: Effects of an external potential on the scattering dynamics of binaries

“…Since one is mainly interested in chaotic encounters, the analysis here pertains chiefly to binary planetesimals in the early solar system (see also Perets 2011), or to binary-single encounters of asteroids or trans-Neptunian objects. For example, take a system with equal masses, each equal to half that of the Pluto-Charon system (see, e.g., Rozner et al 2020;Grishin et al 2020 and references therein), which has m b ≈ 7.3 × 10 −9 M and a0 = 19571 km (Naoz et al 2010), and is situated at r = 39 AU; this system has RH = 401a0. However, in the early solar system, such a binary could have easily existed as close to the Sun as 1 AU, or even much less.…”