Moon is the innermost and largest moon of the Pluto system. Charon was discovered in 1978. Its diameter is 1212 km (753
miles) which is more than half as wide in size as Pluto and the Pluto-Charon
system is like a double planet. Charon orbits Pluto every 6.4 days and has a
synchronous orbit (the pair show the same face to each other all the time). To
an observer on the planet, Charon appears to be stationary in the sky like a
geostationary satellite orbiting the Earth.
Pluto and Charon have been called a double planet because Charon is larger
compared to Pluto.
Two new moons of Pluto were first spotted in May 2005 Hubble Space Telescope
images, then confirmed in archival Hubble pictures taken in June 2002.
The moons were provisionally
designated S/2005 P 1 (Hydra) and S/2005 P 2 (Nix).
June 21, 2006 the International Astronomical Union (IAU) announced
the formal names for Pluto's two discovered small moons: Nix and Hydra. The IAU
chose the name to complement Pluto, who was the Greco-Roman god of the
underworld. Nix represents the Greek goddess of night and Hydra is the
nine-headed monster that guarded Lake Lerna, an entrance to the underworld in
Greek mythology. Nix's off-spring Charon, who ferried souls not the underworld,
lent his name to Pluto's largest moon, which was discovered in 1978.
The correct spelling of Nix is actually Nyx, but as an asteroid had already been
given that name, the IAU accepted the alternative spelling.
Picture: The artist's concept above shows the Pluto
system from the surface of one of the moons. The other members of
the Pluto system are just above the moon's surface. Pluto is the
large disk at center, right. Charon is the smaller disk to the
right of Pluto. The other moon is the bright dot on Pluto's far
left. Credit: NASA, ESA and G. Bacon (STScI)
Hydra is the outer-most natural satellite of Pluto. It was
named after Hydra, the monster who guarded the waters of Pluto / Hades's
underworld in Greco-Roman Mythology. The name Hydra was announced on June 21,
2006, in IAU Circular 8723, along with the formal designation Pluto III. Hydra
is to be visited along with Pluto by the
New Horizons mission in 2015.
At the time of discovery, Hydra was about 25 percent brighter than its sister
moon Nix, which led to the assumption that its diameter was some 10 percent
larger. However, in subsequent observations the two moons were about equal in
brightness. This is likely due to an oblong shape, although brightness variation
over its surface may also be responsible. Hydra appears to be spectrally neutral
like Charon and probably Nix, but unlike Pluto, which is reddish.
Although its size has not been directly measured, calculations based on its
brightness give it a diameter of between 40 km, if its reflectivity is similar
to Charon's 35 percent and about 130 km, if it has a reflectivity of 4 percent
like the darkest
Kuiper belt objects (KBOs).
Kerberos is the fourth moon of Pluto. It was discovered by the
Hubble Space Telescope's Pluto Companion Search Team on 28 June,
2011 using the Wide Field Camera 3. Kerberos is a three-headed dog
in Greek mythology.
is the fifth moon of Pluto is called P5 or S/2012 (134340)
1. It was visible as a speck of light in nine separate Hubble images taken by
Hubble’s Wide Field Camera 3 on 26, 27 and 29 June, and 7 and 9 July 2012.
It is estimated to be irregular in shape and between 10
and 25 km across. It is in a 95 000 km-diameter circular orbit around Pluto that
is assumed to lie in the same plane as Pluto’s other known moons.
Styx is the mythological river separating the living world from the dead.
Kerberos and Styx Naming Contest
Astronomers unveiled a contest to name Pluto's P4 and P5 moons and wanted
the public to help vote the names. The discovery team led by Mark Showalter of the SETI Institute
in Mountain View, California announced on 11 Monday, February 2013 that they
have opened a contest for public voting on the names.
In July 2013, the IAU (International
Astronomical Union) approved 'Kerberos' and 'Styx' as the new
names for two of Pluto’s moons that were previously called P4 and
The IAU selected the names based on the results of the 2013
Pluto Rocks Internet poll sponsored by SETI (the Search for
Extraterrestrial Intelligence), but Vulcan the top vote-getter
ultimately wasn’t chosen as a name for one of the tiny moons. IAU
rules states that Pluto’s moons should be named for mythological
characters of the underworld in Greek and Roman mythology. Dwarf
Planet Pluto is known as the ruler of the underworld in ancient
Did you know?
In 2006 Planet Pluto was controversially reclassified as a Dwarf Planet.
The International Astronomical Union (IAU) is the organization responsible for
naming celestial objects.,
Pluto and Charon : Ice Worlds on the Ragged Edge of the Solar
System by Alan Stern, Jacqueline Mitton
Pluto: The Ninth Planet by Michael D.
Beyond Pluto by John Davies (Author)
Moons of Pluto Links: