On 28 May 2015, NASA presented surprising information, derived from observations by the Hubble Space Telescope, on the behaviors of Pluto and it’s five known moons: Charon, Hydra, Nix, Kerberos, and Styx. Details of the study were reported in the paper, “Resonant Interactions and Chaotic Rotation of Pluto’s Small Moons,” by Douglas Hamilton and Mark Showalter, in the 3 June 2015 issue of Nature.
An artist’s conception of the relative sizes and shapes of Pluto’s known moons is shown in the following figure:
The largest moon, Charon, and Pluto form a binary system that orbits a point between the two, as shown in the following figure, in which Pluto’s orbit is shown in red and Charon’s orbit is shown in green.
As described in my 14 March 2015 post, this binary system behavior also was observed from the New Horizons spacecraft, which is approaching Pluto for a flyby on 14 July 2015.
The Pluto-Charon binary system creates an irregular, rotating, dumbbell-shaped gravitational field that acts on the other moons orbiting the binary pair, resulting in chaotic (unpredictable in the long-term) orbits of the outer moons. The behaviors of Hydra and Nix are further complicated by their non-spherical shapes and tumbling orbital flight. Nonetheless, it appears that the orbits of Hydra, Nix and Styx are synchronized with each other in a 3-body resonance.
You can read more details on the 28 May NASA briefing at the following link:
The New Horizons spacecraft is scheduled for a flyby of Pluto and its five known moons on July 14, 2015. Launched in January 2006, New Horizons has gone through 18 “hibernation” cycles enroute to Pluto. It came out of its last hibernation cycle on December 6, 2014. New Horizons electrical systems are powered by a radioisotope thermoelectric generator (RTG) that produces electricity from the heat of decaying Plutonium 238. Propulsion is by means of hydrazine thrusters.
New Horizons spacecraft. Source: NASA
You can find details on the design of the New Horizons spacecraft at the following link:
New Horizons trajectory from Earth included a gravity-assist from Jupiter.
Here’s a New Horizons photo of Jupiter during it’s 2007 flyby:
Pluto and moon Charon viewed from New Horizons in January 2015:
You can see an interesting NASA time-lapse “video” sequence of Charon circling Pluto at the following link:
As noted in that article, Charon’s mass is roughly a tenth of Pluto’s, which gives it enough gravitational pull to have a noticeable effect on Pluto’s position.
You can follow details on the New Horizons mission on the following NASA website:
After the Pluto encounter, New Horizons will continue on to visit one or more objects in the Kuiper Belt, which circles our solar system beyond the orbit of Pluto. The Hubble space telescope has been used to search for potential Kuiper Belt Objects (KBOs).