Charon Moon Facts

Charon is the largest and innermost moon of Pluto. It was discovered in 1978 by astronomer James Christy and is nearly 1/8 the mass of Pluto. It orbits a common centre of gravity with Pluto, and the two worlds are tidally locked together as they orbit.

Moon Profile

Diameter: 1,208 km
Mass: 1.52 x 10^21 kg (2.54 x 10^-4 Earths)
Orbits: a common barycentre with Pluto
Average Distance from Pluto: 19,570 km
Length of Orbit: 6.387 days
Surface Temperature: -230 °C

Pluto’s Moons (Size & Orbits)

Facts about Charon

Charon was named for the Greek mythological figure Charon, the ferryman to Styx: It has two different pronunciations: “SHARE-on”, in honour of the discoverer’s wife’s name (used) NASA and the members of the New Horizons mission), and “CARE-on”, for those who prefer the Greek pronunciation.

If it were not orbiting Pluto, Charon would be a dwarf planet in its own right: It may yet be determined a dwarf planet, particularly because it doesn’t orbit Pluto – instead, the two worlds orbit a common centre of gravity. As they move, they keep the same face toward each other because they are tidally locked.

Charon has a frigid surface, covered with methane and nitrogen ice, and possibly some water ice: Although Charon is mostly ice by mass, it may contain a small rocky core.

Charon MAY have ‘ice volcanoes’: Observations made by ground-based observers at the Gemini Observatory in Hawaii determined that Charon MAY have ice-particle geysers, a form of cryovolcanism.

Pluto and Charon have never been visited by a spacecraft: Although both have been observed by Hubble Space Telescope as well as ground-based observatories. The New Horizons mission was sent to fly past Pluto and Charon and gather information and images about these worlds.

Charon’s origin is still not completely understood: One theory suggests that Charon was created when a neighbouring Kuiper Belt object collided with Pluto. That destroyed the impactor, sending chunks of debris into orbit around Pluto. Eventually the chunks reassembled themselves to create Charon. Another idea suggests that infant Pluto and Charon collided, but did not break apart. Instead they went into orbit around each other.

Charon has a canyon that is 7 to 9 km deep:
For comparison Mount Everest is 8.8 km high. Other extensive cliffs and troughs stretching around 1,000 km have also been observed on Charon’s surface.

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Triton Moon Facts

Triton is Neptune’s largest moon and is the only large moon in the solar system to orbit in the opposite direction to its planet’s rotation, this is known as a retrograde orbit.

Moon Profile

Diameter: 2706.8 km
Mass: 2.14 x 10 ^ 22 lg
Orbits: Neptune
Average Distance from Neptune: 354,759 km
Length of Orbit: -5.8 days (retrograde)
Surface Temperature: 38 K (-135.15 C)

Facts about Triton

• Triton is a frozen wonderland, exhibiting a strange array of terrain types. Its icy surface has craters, geysers, and rugged landscape called “cantaloupe terrain”. These all indicate some sort of activity going on inside, and cryovolcanism spouting material to the surface.
• The geysers of Triton spewing nitrogen gas out from beneath the surface into long plumes that rise as high as 8 kilometres. As a result, Triton has a very thin nitrogen atmosphere.
• The southern polar cap of Triton is covered with frozen nitrogen and methane. There may be a north polar cap as well.
• Triton could be divided into layers of ice around a rocky core. The crust is largely water ice. There could be subsurface ocean of slushy or liquid water.
• Triton orbits Neptune in retrograde — that is, opposite to the direction of Neptune’s rotation on its axis. This may imply that Triton was captured by Neptune’s gravity into its inclined orbit.
• Triton rotates once on its axis as it orbits the planet. It keeps the same face toward Neptune at all times.
• Triton will wander too close to Neptune in its orbit in about 3.5 billion years, and the gravitational pull of the planet will break Triton up. The result will be a ring system.
• Voyager 2 was the only spacecraft to visit and map Triton. It flew by in 1989. There are no other missions planned to Neptune or Triton for the foreseeable future.

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Miranda Moon Facts

Miranda is the smallest of the rounded satellites of Uranus. It also orbits the closest of the five larger moons. It is named after one of the characters in Shakespeares play, “The Tempest”. It was also featured in Arthur C. Clark’s novel “2001: A Space Odyssey”.

Moon Profile

Diameter: 470 km
Mass: 6.6 x 10 ^19 kg
Orbits: Uranus
Average Distance from Uranus: 129,390 km
Length of Orbit: 1.4 days
Surface Temperature: 60 K (-213.5)

Facts about Miranda

• Miranda was discovered in 1948 by astronomer Gerard Kuiper. The Kuiper Belt of the outer solar system is named for him.
• Miranda is made largely of ice with some rocky material closer to its centre.
• No two surface areas on Miranda are alike. Its topography ranges from cliffs to craters, and tectonic features.
• Verona Rupes is the largest cliff in the solar system. It rises up some 20 kilometres above the surrounding landscape. It may have formed when the surface faulted and cracked, causing part of it to drop.
• Miranda’s surface has several tectonic regions that look like raceways called coronae. One of them has a “checkmark” shaped feature in the centre.
• Miranda is one of the smallest bodies in the solar system to be self-rounded under its own gravity.
• Miranda has experienced geological activity that was likely caused by tidal heating when this little moon was in orbital resonance with its neighbour Umbriel.
• The Voyager 2 spacecraft is the only mission to fly close enough to image Miranda. There are no other missions to Miranda planned at this time.

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Iapetus Moon Facts

Iapetus is an oddly-colored and shaped moon of Saturn. It is the third-largest moon in the system, and was discovered in 1671 by the astronomer Giovanni Domenico Cassini.

Moon Profile

Diameter: 1,469 km
Mass: 1.8 x 10 ^ 21 kg
Orbits: Saturn
Average Distance from Saturn: 3,560,820 km
Length of Orbit: 79.3 days
Surface Temperature: 90 to 130 K (-183.15 to -143.15 C)

Facts about Iapetus

• Iapetus comes from the name of a Greek Titan, following along in the tradition of calling Saturn’s moons after the Titans.
• Iapetus has a bright and a dark hemisphere, with a ridge running along its equator. The dark region is called Cassini Regio and is the principal feature of the leading hemisphere.
• The surface of Iapetus is heavily cratered, with large impact basins up to 580 kilometres across.
• Surface darkening on Iapetus comes from organic materials left behind as ice in the warmer Cassini Region region sublimates. The dark patches seem to be made of organic materials similar to those found in early meteorites or comets. There is also a suggestion that some material may have come from outside Iapetus.
• Iapetus’s equatorial ridge runs along 1,300 kilometres through the central region of the moon. It is about 20 kilometres wide and towers up 13 kilometres over the surrounding surface. No one is quite sure why or how it formed.
• The Voyager and Cassini missions have led in the exploration of Iapetus. Cassini has been able to study it over longer periods of time.
• Iapetus’s orbit is inclined to the plane of Saturn and is also quite far away. This makes it the only large moon from which an observer could see the rings.
• There currently no missions planned to explore Iapetus in the near future.

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Enceladus Moon Facts

Enceladus is the sixth-largest moon of Saturn and, after Titan, one of the most-studied worlds in the system. It was discovered in 1789 by William Herschel and named after the Greek mythological giant Enceladus.

Moon Profile

Dimensions: 504 km
Mass: 1.08 x 10 ^20 kg
Orbits: Saturn
Average Distance from Saturn: 237,948 km
Length of Orbit: 1.37 days
Surface Temperature: 75K (-198 C)

Facts about Encladus

• Enceladus was first studied in detail by the Voyager spacecraft. The Cassini mission did close flybys of this moon, to map its surface in high resolution.
• Enceladus is a largely icy world with some percentage of its mass being silicates. It appears to have a rocky core mixed with with water ice, and a frozen mantle.
• Cryovolcanic activity in Enceladus is sending geysers of water ice particles out from underneath the surface. The Cassini spacecraft has imaged these geysers spouting from so-called “tiger stripes” vent areas on this moon.
• The icy particles from Enceladus spread out to space and feed the nearby E-ring with material.
• The volcanic action on Enceladus led scientists to suggest that a liquid water ocean lies under the surface of this moon, and is feeding the geysers seen by Cassini.
• Enceladus is thought to be heated from within by either radioactive heating (the decay of radioactive elements in the core) or tidal flexing as Saturn’s immense gravity pulls on the moon.
• Future missions have been proposed to explore Enceladus and perhaps bring back samples of its icy plume material. These would also study the other moons of Saturn, plus the ring system.
• As with Europa at Jupiter, scientists suspect that Enceladus could be a habitable world to some forms of life. There is no proof of life there, but future missions could test for life signs.
• Enceladus is now known to have a subsurface ocean made of liquid water. Images from the Cassini spacecraft helped mission scientists deduce and prove the existence of that ocean.

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