A Pluto–Charon Sonata: The Dynamical Architecture of the Circumbinary Satellite System

Abstract

Using a large suite of n-body simulations, we explore the discovery space for new satellites in the Pluto-Charon system. For the adopted masses and orbits of the known satellites, there are few stable prograde or polar orbits with semimajor axes a 1.1 a H , where a H is the semimajor axis of the outermost moon Hydra. Small moons with radii r 2 km and a 1.1 a H are ejected on time scales ranging from several yr to more than 10 Myr. Orbits with a 1.1 a H are stable on time scales exceeding 100 Myr. Near-IR and mid-IR imaging with JWST and ground-based occultation campaigns with 2-3-m class telescopes can detect 1-2 km satellites outside the orbit of Hydra. Searches for these moons enable new constraints on the masses of the known satellites and on theories for circumbinary satellite formation.Subject headings: planets and satellites: dynamical evolution and stabilityplanets and satellites: individual (Pluto)

On the Origin of the Pluto System

“…If Charon's eccentricity reaches the values expected in current tidal models (Cheng et al, 2014b), some or all of the satellites except Hydra become dynamically unstable on their present-day orbits (Smullen and Kratter, 2017). As mentioned above, this model also predicts the growth and survival of small satellites exterior to Hydra (e.g., Kenyon and Bromley, 2019); such satellites have not been seen to date (section 2.3). Walsh and Levison (2015) considered the evolution of debris from one or more disrupted outer satellites that formed as a result of a Charon-forming impact.…”

“…High small moon albedos were first predicted from the dynamical models of Youdin et al (2012), who found that lower albedos, which required larger moon masses for consistency with HST data, would lead to dynamical instability. Subsequent orbital analyses have confi rmed that stability requires high albedos and low moon masses, and in the case of Hydra, have pushed its estimated mass to even lower values (Brozović et al, 2015;Kenyon and Bromley, 2019;Jacobson et al, 2019).…”

“…Smaller regular moons -if they existcould be dynamically stable out to 5 × 10 5 km ~ 400 R P , i.e, ~0.1 Pluto-Charon Hill radii (Michaely et al, 2017). Bodies down to 1-2 km in size (~10 9 kg) will be detectable with the upcoming James Webb Space Telescope, and if they exist, could help constrain the masses of the known small moons (Kenyon and Bromley, 2019). New Horizons also conducted an extensive search for rings comparable to those surrounding other solar system bodies, but no such structures at Pluto were seen (Lauer et al, 2018).…”

“…From Arakawa et al (2019). requires high albedos and low moon masses, and in the case of Hydra, have pushed its estimated mass to even lower values (Brozović et al, 2015;Kenyon and Bromley, 2019;Jacobson et al, 2019).…”

A Pluto–Charon Sonata IV. Improved Constraints on the Dynamical Behavior and Masses of the Small Satellites

“…Albedos are ∼55% for Kerberos and Nix, 65% for Styx, and 85% for Hydra (Weaver et al 2016). Although smaller satellites could exist slightly inside the orbit of Styx and outside the orbit of Hydra (Kenyon & Bromley 2019b), there are no 2 km satellites and a negligible amount of dust between the orbits of Styx and Hydra (Weaver et al 2016;Lauer et al 2018).…”