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Title: CIRCUMBINARY CHAOS: USING PLUTO'S NEWEST MOON TO CONSTRAIN THE MASSES OF NIX AND HYDRA

Abstract

The Pluto system provides a unique local laboratory for the study of binaries with multiple low-mass companions. In this paper, we study the orbital stability of P4, the most recently discovered moon in the Pluto system. This newfound companion orbits near the plane of the Pluto-Charon (PC) binary, roughly halfway between the two minor moons Nix and Hydra. We use a suite of few body integrations to constrain the masses of Nix and Hydra, and the orbital parameters of P4. For the system to remain stable over the age of the solar system, the masses of Nix and Hydra likely do not exceed 5 Multiplication-Sign 10{sup 16} kg and 9 Multiplication-Sign 10{sup 16} kg, respectively. These upper limits assume a fixed mass ratio between Nix and Hydra at the value implied by their median optical brightness. Our study finds that stability is more sensitive to their total mass and that a downward revision of Charon's eccentricity (from our adopted value of 0.0035) is unlikely to significantly affect our conclusions. Our upper limits are an order of magnitude below existing astrometric limits on the masses of Nix and Hydra. For a density at least that of ice, the albedos of Nixmore » and Hydra would exceed 0.3. This constraint implies they are icy, as predicted by giant impact models. Even with these low masses, P4 only remains stable if its eccentricity e {approx}< 0.02. The 5:1 commensurability with Charon is particularly unstable, combining stability constraints with the observed mean motion places the preferred orbit for P4 just exterior to the 5:1 resonance. These predictions will be tested when the New Horizons satellite visits Pluto. Based on the results for the PC system, we expect that circumbinary, multi-planet systems will be more widely spaced than their singleton counterparts. Further, circumbinary exoplanets close to the three-body stability boundary, such as those found by Kepler, are less likely to have other companions nearby.« less

Authors:
; ;  [1]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
22039169
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 755; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALBEDO; ASTRONOMY; ASTROPHYSICS; BRIGHTNESS; CHAOS THEORY; DENSITY; ICE; MASS; MOON; ORBITS; PLUTO PLANET; RESONANCE; SOLAR SYSTEM; SOLAR SYSTEM EVOLUTION; STABILITY; THREE-BODY PROBLEM

Citation Formats

Youdin, Andrew N., Kratter, Kaitlin M., and Kenyon, Scott J.. CIRCUMBINARY CHAOS: USING PLUTO'S NEWEST MOON TO CONSTRAIN THE MASSES OF NIX AND HYDRA. United States: N. p., 2012. Web. doi:10.1088/0004-637X/755/1/17.
Youdin, Andrew N., Kratter, Kaitlin M., & Kenyon, Scott J.. CIRCUMBINARY CHAOS: USING PLUTO'S NEWEST MOON TO CONSTRAIN THE MASSES OF NIX AND HYDRA. United States. doi:10.1088/0004-637X/755/1/17.
Youdin, Andrew N., Kratter, Kaitlin M., and Kenyon, Scott J.. Fri . "CIRCUMBINARY CHAOS: USING PLUTO'S NEWEST MOON TO CONSTRAIN THE MASSES OF NIX AND HYDRA". United States. doi:10.1088/0004-637X/755/1/17.
@article{osti_22039169,
title = {CIRCUMBINARY CHAOS: USING PLUTO'S NEWEST MOON TO CONSTRAIN THE MASSES OF NIX AND HYDRA},
author = {Youdin, Andrew N. and Kratter, Kaitlin M. and Kenyon, Scott J.},
abstractNote = {The Pluto system provides a unique local laboratory for the study of binaries with multiple low-mass companions. In this paper, we study the orbital stability of P4, the most recently discovered moon in the Pluto system. This newfound companion orbits near the plane of the Pluto-Charon (PC) binary, roughly halfway between the two minor moons Nix and Hydra. We use a suite of few body integrations to constrain the masses of Nix and Hydra, and the orbital parameters of P4. For the system to remain stable over the age of the solar system, the masses of Nix and Hydra likely do not exceed 5 Multiplication-Sign 10{sup 16} kg and 9 Multiplication-Sign 10{sup 16} kg, respectively. These upper limits assume a fixed mass ratio between Nix and Hydra at the value implied by their median optical brightness. Our study finds that stability is more sensitive to their total mass and that a downward revision of Charon's eccentricity (from our adopted value of 0.0035) is unlikely to significantly affect our conclusions. Our upper limits are an order of magnitude below existing astrometric limits on the masses of Nix and Hydra. For a density at least that of ice, the albedos of Nix and Hydra would exceed 0.3. This constraint implies they are icy, as predicted by giant impact models. Even with these low masses, P4 only remains stable if its eccentricity e {approx}< 0.02. The 5:1 commensurability with Charon is particularly unstable, combining stability constraints with the observed mean motion places the preferred orbit for P4 just exterior to the 5:1 resonance. These predictions will be tested when the New Horizons satellite visits Pluto. Based on the results for the PC system, we expect that circumbinary, multi-planet systems will be more widely spaced than their singleton counterparts. Further, circumbinary exoplanets close to the three-body stability boundary, such as those found by Kepler, are less likely to have other companions nearby.},
doi = {10.1088/0004-637X/755/1/17},
journal = {Astrophysical Journal},
number = 1,
volume = 755,
place = {United States},
year = {Fri Aug 10 00:00:00 EDT 2012},
month = {Fri Aug 10 00:00:00 EDT 2012}
}
  • It is generally believed that Charon was formed as a result of a large, grazing collision with Pluto that supplied the Pluto-Charon system with its high angular momentum. It has also been proposed that Pluto's small outer moons, Nix and Hydra, formed from debris from the Charon-forming impact, although the viability of this scenario remains unclear. Here I use smooth particle hydrodynamics impact simulations to show that it is possible to simultaneously form an intact Charon and an accompanying debris disk from a single impact. The successful cases involve colliding objects that are partially differentiated prior to impact, having thinmore » outer ice mantles overlying a uniform composition rock-ice core. The composition of the resulting debris disks varies from a mixture of rock and ice (similar to the bulk composition of Pluto and Charon) to a pure ice disk. If Nix and Hydra were formed from such an impact-generated disk, their densities should be less than or similar to that of Charon and Pluto, and the small moons could be composed entirely of ice. If they were instead formed from captured material, a mixed rock-ice composition and densities similar to that of Charon and Pluto would be expected. Improved constraints on the properties of Nix and Hydra through occultations and/or the New Horizons encounter may thus help to distinguish between these two modes of origin, particularly if the small moons are found to have ice-like densities.« less
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