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Pluto and its Moons

This app shows a real-time display of Pluto and its moons. It also shows the flight path of the New Horizons spacecraft as a red line running through the system.

The data for the above display was derived from the NASA's JPL website and covers the period 1900 to 2100 AD. Because of the difficulties in observing the plutonian system, the accuracy of the orbits will likely be refined in the future. Also, outside of the time frame mentioned above, the positions of the moons shown is an approximation.

With the app at the default settings the image (orbits and planets) are all to scale.

Plutonian System

The plutonian system, shown above, initially looks like all the moons are in squashed elliptical orbits. This is only because the view shown is perpendicular to the plane of the ecliptic and Pluto’s moons don't move in the plane of the ecliptic.

By turning on the 3D view you can see that the orbits are actually pretty circular but at an angle to the ecliptic. e.g. it's like we're looking at a plate from a side on angle.

New Horizons

On July 14th 2015, Pluto was visited by the New Horizons spacecraft. This spacecraft sent back an enormous amount of data and the first clear images of the Plutonian system.

The Plutonian System

The plutonian system moves about the sun in a plane that is at an angle of 17 degrees to the plane of the ecliptic. Pluto and its moons also orbit about each other in a plane which is at an angle of 120 degrees to its orbit about the sun. The result is that the dwarf planet and its moons rotate at a steep angle of around 60 degrees to the plane of the ecliptic and are rotating oppositely to most other planets.

The orbits of all the moons about the system barycentre appear to be very close to circular.

The orbits of the moons appear to be stabilised by being in resonance with each other. Styx, Nix, Kerberos and Hydra are fairly close to 3:1, 4:1, 5:1 and 6:1 mean-motion orbital resonances with that of Charon.



NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. The image combines blue, red and infrared images taken by the Ralph/Multispectral Visual Imaging Camera (MVIC). Pluto’s surface sports a remarkable range of subtle colors, enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have their own distinct colors, telling a complex geological and climatological story that scientists have only just begun to decode. The image resolves details and colors on scales as small as 0.8 miles (1.3 kilometers). The viewer is encouraged to zoom in on the full resolution image on a larger screen to fully appreciate the complexity of Pluto’s surface features. Credit: NASA/JHUAPL/SwRI



NASA's New Horizons spacecraft captured this high-resolution, enhanced color view of Pluto’s largest moon, Charon, just before closest approach on July 14, 2015. The image combines blue, red and infrared images taken by the spacecraft's Ralph/Multispectral Visual Imaging Camera (MVIC); the colors are processed to best highlight the variation of surface properties across Charon. Scientists have learned that reddish material in the north (top) polar region – informally named Mordor Macula – is chemically processed methane that escaped from Pluto’s atmosphere onto Charon. Charon is 754 miles (1,214 kilometers) across; this image resolves details as small as 1.8 miles (2.9 kilometers). Credits: NASA/JHUAPL/SwRI

Charon was discovered by James Christy in 1978 by examining some magnified photographic plates imaged using the 1.55 meter telescope based at the United States Naval Observatory Flagstaff Station. Originally named Charon after Christy's wife, Charlene, it was eventually officially named "Charon" after the mythical Greek ferryman of the dead who coincidentally was linked to the Greek god Hades - the equivalent of Romes god Pluto.

Charon is thought to be mostly made of water ice and rock with some traces of ammonia hydrates.

Pluto and its largest moon, Charon, form a binary system rather than a typical planet-moon relationship.

Charon at 1205km diameter (as confirmed by New Horizons 13/7/2015) weighs 12% of Pluto (at 2370km - as measured by New Horizons 13/7/2015) and both bodies rotate about a point (known as the barycentre) which lies 2000km from Pluto's centre and 17,500km from Charon. Both bodies are gravitationally locked to each other so that they both orbit and rotate with the same periodicity. This means they always show the same face to each other.


Styx image from New Horizons

Styx was the latest of the moons to be discovered and was detected by the Hubble space telescope in 2012 whilst the New Horizons probe was in flight.

It is thought to have a diameter between 10 and 25km which has been guessed at by knowing its brightness and guessing appropriate surface albedo (surface colour/darkness).

It was named after the Roman river goddess Styx who is named after the mythical river of the same name.


Nix with enhanced Colour

Pluto's moon Nix, shown here in enhanced color as imaged by the New Horizons Ralph instrument, has a reddish spot that has attracted the interest of mission scientists. The data were obtained on the morning of July 14, 2015, and received on the ground on July 18. At the time the observations were taken New Horizons was about 102,000 miles (165,000 km) from Nix. The image shows features as small as approximately 2 miles (3 kilometers) across on Nix, which is estimated to be 26 miles (42 kilometers) long and 22 miles (36 kilometers) wide. Click for full story. Image Credit: By NASA/JHU-APL/SwRI/Roman Tkachenko - Roman Tkachenko, Public Domain,

Both Nix and Hydra were discovered using the Hubble Space Telescope imagery in June 2005. It was thought to have a diameter of between 46km and 137km which has been derived from knowledgeable guesswork.

New Horizons images show an elongated body about 42km (26 miles) long and 36km (22miles) wide.

Although the overall surface color of Nix is neutral grey, the image above (colour enhanced) shows a region that has a distinct red tint. Hints of a bull's-eye pattern lead scientists to speculate that the reddish region is a crater.

Nix was named after Nyx, the 'reek goddess of darkness and night and mother of Charon. The spelling was changed to prevent a clash with an already named "Nyx" asteroid.


Kerberos from New Horizons

Kerberos imaged by New Horizons on 14 July from a distance of 396,100 km

Discovered in 2011 using Hubble space telescope images, this moon estimates in at between 13km to 34km and orbits the system once every 32 days.

Kerberos was named after Cerberus, (the dog that guards Pluto's underworld), but due to Cerberus already being used for an Asteroid, the Greek spelling "Kerberos" was accepted.


Pluto's Moon Hydra

Pluto's small, irregularly shaped moon Hydra is revealed in this black and white image taken from New Horizons' LORRI instrument on July 14, 2015 from a distance of about 143,000 miles (231,000 kilometers). Features as small as 0.7 miles (1.2 kilometers) are visible on Hydra, which measures 34 miles (55 kilometers) in length. Click for full Story. Image Credit: NASA-JHUAPL-SWRI.

Discovered at the same time as Nix (2005), Hydra was estimated at between 61km and 167km. The New Horizons image above shows the tiny potato-shaped moon to be 55 km (34 miles) in length.

The furthest moon from Pluto, it orbits the system at a distance of 65,000km with a period of once every 38 days.

It's named after the Greek Hydra - a nine headed monster - which is a reference to Pluto's tenure as the ninth planet of the solar system.