The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of ~40 kilometers for Nix and Hydra and ~10 kilometers for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of ~2. All four moons have high albedos (~50 to 90%) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages of at least 4 billion years. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary.
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Resonant Interactions and Chaotic Rotation of Pluto's Small MoonsMR Showalter et al. Nature 522 (7554), 45-9. PMID 26040889.Four small moons--Styx, Nix, Kerberos and Hydra--follow near-circular, near-equatorial orbits around the central 'binary planet' comprising Pluto and its large moon, Char …
The Pluto System: Initial Results From Its Exploration by New HorizonsSA Stern et al. Science 350 (6258), aad1815. PMID 26472913.The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain age …
Forced Resonant Migration of Pluto's Outer Satellites by CharonWR Ward et al. Science 313 (5790), 1107-9. PMID 16825533.Two small moons of Pluto have been discovered in low-eccentricity orbits exterior to Pluto's large satellite, Charon. All three satellite orbits are nearly coplanar, impl …
A Giant Impact Origin for Pluto's Small Moons and Satellite Multiplicity in the Kuiper BeltSA Stern et al. Nature 439 (7079), 946-8. PMID 16495992.The two newly discovered satellites of Pluto (P1 and P2) have masses that are small compared to both Pluto and Charon-that is, between 5 x 10(-4) and 1 x 10(-5) of Pluto' …
Discovery of Two New Satellites of PlutoHA Weaver et al. Nature 439 (7079), 943-5. PMID 16495991.Pluto's first known satellite, Charon, was discovered in 1978. It has a diameter (approximately 1,200 km) about half that of Pluto, which makes it larger, relative to its …
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The Formation of Charon's Red Poles From Seasonally Cold-Trapped VolatilesWM Grundy et al. Nature 539 (7627), 65-68. PMID 27626378.A unique feature of Pluto's large satellite Charon is its dark red northern polar cap. Similar colours on Pluto's surface have been attributed to tholin-like organic macr …