This photo of Neptune's satellite (moon) Triton was taken in 1989 by the only spacecraft ever to pass Triton: Voyager 2. V2 found fascinating terrain, a thin atmosphere and even evidence of ice volcanoes.
Title: Why Does Neptune's Moon, Triton, Orbit Backwards? Published on Mar 1 2016 YouTube Code: https://youtu.be/aP7IpFVts9I Duration: 4:42
This composite image shows a sliver of Pluto's large moon, Charon, and all four of Pluto's small moons, as resolved by the Long Range Reconnaissance Imager (LORRI) on the New Horizons spacecraft. Image Credit: NASA/JHUAPL/SwRI
It is intriguing that such a small planet can have such a complex collection of satellites. The discovery provides additional clues for unraveling how the Pluto system formed and evolved.
Pluto's entire moon system is believed to have formed by a collision between two the dwarf planet and another Kuiper Belt Object early in the history of the solar system. The smashup flung material that coalesced into the family of satellites observed around Pluto.
"The moons form a series of neatly nested orbits, a bit like Russian dolls," said Mark Showalter of the SETI Institute.
The known moons of Pluto are: Charon: Discovered in 1978, this small moon is almost half the size of Pluto. It is so big Pluto and Charon are sometimes referred to as a double planet system.
Nix and Hydra: These small moons were found in 2005 by a Hubble Space Telescope team studying the Pluto system.
Kerberos: Discovered in 2011, this tiny moon is located between the orbits of Nix and Hydra.
Styx: Discovered in 2012, this little moon was found by a team of scientists searching for potential hazards to the New Horizons spacecraft Pluto flyby in July 2015.
How Pluto Moons Get Their Names All of Pluto's moons are named for mythological figures associated with the underworld, a naming conventions started by 11-year-old Venetia Burney in 1930.Christy proposed the name Charon after the mythological ferryman who carried souls across the river Acheron, one of the five mythical rivers that surrounded Pluto's underworld. Apart from the mythological connection for this name, Christy chose it because the first four letters also matched the name of his wife, Charlene.
01. Charon Moon Data Mass (kg) 1.90e+21 Radius (km) 586 Density (gm/cm3) 1.83 Distance from Pluto (km) 19,640 Period of rotation (days) 6.38725 Period of orbit (days) 6.38725 Orbital velocity (km/sec) 0.23 Eccentricity of orbit 0.00 Inclination of orbit (°) 98.80 Escape velocity (km/sec) 0.610 Visual albedo 0.5 Visual magnitude 16.8 Discovered: 1978 J.Cristy
The largest of Pluto's five moons, Charon, was discovered 40 years ago in June 1978 by James Christy and Robert Harrington at the U.S. Naval Observatory in Flagstaff, Arizona―only about six miles from where Pluto itself was discovered at Lowell Observatory. They weren't even looking for moons. They were trying to refine Pluto's orbit around the Sun.
Discovery Charon was discovered in 1978 when sharp-eyed astronomer James Christy noticed images of Pluto were strangely elongated. The blob seemed to move around Pluto. The direction of elongation cycled back and forth over 6.39 days―Pluto's rotation period. Searching through their archives of Pluto images taken years before, Christy found more cases where Pluto appeared elongated. Additional images confirmed he had discovered the first known moon of Pluto.
Overview At half the size of Pluto, Charon is the largest of Pluto's moons and the largest known satellite relative to its parent body. Pluto-Charon is our solar system's only known double planetary system. The same surfaces of Charon and Pluto always face each other, a phenomenon called mutual tidal locking. Charon orbits Pluto every 6.4 Earth days.
In Depth Charon is almost half the size of Pluto. The little moon is so big that Pluto and Charon are sometimes referred to as a double dwarf planet system. The distance between them is 19,640 km (12,200 miles).
The Hubble Space Telescope photographed Pluto and Charon in 1994 when Pluto was about 30 AU from Earth. These photos showed that Charon is more neutral grey than Pluto (which has a red tinge), indicating that they have different surface compositions and structure.
Charon's orbit around Pluto takes 6.4 Earth days, and one Pluto rotation (a Pluto day) takes 6.4 Earth days. Charon neither rises nor sets, but hovers over the same spot on Pluto's surface, and the same side of Charon always faces Pluto―this is called tidal locking. Compared with most of the planets and moons, the Pluto-Charon system is tipped on its side, like Uranus. Pluto's rotation is retrograde: it rotates backwards, from east to west (Uranus and Venus also have retrograde rotations).
