Kerberos, formal designation (134340) Pluto IV, is a small natural satellite of Pluto, about in its longest dimension. Kerberos is also the second-smallest moon of

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

, after Styx. It was the fourth moon of Pluto to be discovered and its existence was announced on 20 July 2011. It was imaged, along with

and its four other moons, by the ''

New Horizons ''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institut ...

'' spacecraft in July 2015. The first image of Kerberos from the flyby was released to the public on 22 October 2015.

Discovery

Kerberos was discovered by researchers of the Pluto Companion Search Team using the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

on 28 June 2011, using the Wide Field Camera 3, during an attempt to find any rings that Pluto might possess. The search for rings was motivated in part by a desire to avoid damage to ''

'' when it passed through the Pluto system in July 2015. Further observations were made on 3 and 18 July 2011 and Kerberos was verified as a new moon on 20 July 2011. It was later precovered or identified in earlier archival Hubble images from 15 February 2006 and 25 June 2010, though Kerberos was obscured by diffraction spikes in those images. Kerberos's brightness is only about 10% of that of Nix, and it was only found because the discovery team took eight-minute exposures; earlier observations had used shorter exposures. It was officially designated S/2011 (134340) 1, and was informally referred to as P4.

Origin

Like Pluto's other moons, it is suspected that Kerberos coalesced from the debris of a massive collision between Pluto and another

Kuiper belt The Kuiper belt ( ) is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...

object, similar to the giant impact thought to have created the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

Physical characteristics

Kerberos has a double-lobed shape and is approximately across its longest dimension and across its shortest dimension. It is the second-smallest of Pluto's moons, after Styx. The larger lobe of Kerberos is approximately 8 km (5 mi) across while the smaller lobe is measured to be approximately across. The double-lobed shape of Kerberos is likely formed by two smaller objects merged, suggesting that Kerberos along with Pluto's other moons may have been formed by the coalescence of debris around Pluto. Kerberos has a high

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

or reflectivity similar to Pluto's other small moons, likely due to the presence of water ice on its surface. Before the ''New Horizons'' flyby, Kerberos was initially thought to have a larger size and a darker surface.

Rotation

Like the other small moons of Pluto, Kerberos is not tidally locked and its rotation is chaotic, varying quickly over geological timescales. The varying gravitational influences of Pluto and

Charon In Greek mythology, Charon or Kharon ( ; ) is a psychopomp, the ferryman of the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the worlds of the living and ...

as they orbit their

barycenter In astronomy, the barycenter (or barycentre; ) is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. A barycenter is a dynamical point, not a physical object. It is an important con ...

causes the chaotic tumbling of Pluto's small moons, including Kerberos. At the time of the ''New Horizons'' flyby, the rotational period of Kerberos was about 5.33 days and its rotational axis was tilted about 96 degrees to its orbit. The high axial tilt of Kerberos meant that it was rotating sideways relative to its orbit around the Pluto-Charon barycenter.

Orbit

Observations indicate a circular, equatorial orbit around the Pluto-Charon barycenter at a distance of . All of Pluto's moons including Kerberos have very circular orbits with very low

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

s to Pluto's equator. Kerberos orbits between Nix and Hydra and makes a complete orbit around Pluto roughly every 32.167 days. Its orbital period is close to a 1:5

orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...

with

, with the timing discrepancy being about 0.7%. As with the near resonances between Nix or Hydra and Charon (1:4 and 1:6, respectively), determining how close this relationship is to a true resonance will require more-accurate knowledge of Kerberos's orbit, in particular its rate of

precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In o ...

Exploration

The ''

'' spacecraft took images of Kerberos during its flyby of the Pluto system on 14 July 2015. Three months later, on 22 October, the first image of the moon was published. It is the last moon of Pluto to have its image released, revealing that Kerberos was small and had a bright surface contrary to the initial idea that the moon was covered in dark material.

Naming

Upon discovery, Kerberos received the minor planet designation S/2011 (134340) 1 because it was the first satellite (S) discovered orbiting the

minor planet According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...

134340 Pluto in 2011. It was initially called "P4", indicating that it was the fourth Plutonian moon to be discovered. The convention for naming Plutonian moons is to use names associated with the god

classical mythology Classical mythology, also known as Greco-Roman mythology or Greek and Roman mythology, is the collective body and study of myths from the ancient Greeks and ancient Romans. Mythology, along with philosophy and political thought, is one of the m ...

. To decide on names for P4 and P5, Mark Showalter and the

SETI Institute The SETI Institute is a not-for-profit research organization incorporated in 1984 whose mission is to explore, understand, and explain the origin and nature of life in the universe, and to use this knowledge to inspire and guide present and futu ...

, on behalf of the discovery team, conducted a non-binding Internet poll in 2013, in which the general public was invited to vote for their favorite names. The public could choose from a selection of Greek mythological names related to the god Pluto, or could propose their own names. After the initial announcement,

William Shatner William Shatner (born March 22, 1931) is a Canadian actor. In a career spanning seven decades, he is best known for his portrayal of James T. Kirk in the ''Star Trek'' franchise, from his 1966 debut as the captain of the starship USS Enterpri ...

, the actor who played Captain James T. Kirk in the ''

Star Trek ''Star Trek'' is an American science fiction media franchise created by Gene Roddenberry, which began with the Star Trek: The Original Series, series of the same name and became a worldwide Popular culture, pop-culture Cultural influence of ...

'' franchise, proposed the names Vulcan and Romulus, ostensibly referring to the fire god Vulcan (a nephew of Pluto), and to

Romulus Romulus (, ) was the legendary founder and first king of Rome. Various traditions attribute the establishment of many of Rome's oldest legal, political, religious, and social institutions to Romulus and his contemporaries. Although many of th ...

the founder of

Rome Rome (Italian language, Italian and , ) is the capital city and most populated (municipality) of Italy. It is also the administrative centre of the Lazio Regions of Italy, region and of the Metropolitan City of Rome. A special named with 2, ...

, but also alluding to the fictional planets of Vulcan and

in the ''Star Trek'' universe. The "Romulus" suggestion was discounted, because there is already an asteroid moon of that name, but Vulcan won the poll after Shatner tweeted about it, with

Cerberus In Greek mythology, Cerberus ( or ; ''Kérberos'' ), often referred to as the hound of Hades, is a polycephaly, multi-headed dog that guards the gates of the Greek underworld, underworld to prevent the dead from leaving. He was the offspring o ...

(the dog that guards Pluto's underworld) coming second and

Styx In Greek mythology, Styx (; ; lit. "Shuddering"), also called the River Styx, is a goddess and one of the rivers of the Greek Underworld. Her parents were the Titans Oceanus and Tethys, and she was the wife of the Titan Pallas and the moth ...

(the goddess of the river of the underworld) coming third. The winning names were submitted to the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

. However, "Vulcan" was unacceptable to the IAU because it was not the name of an underworld deity and had already been used for a hypothetical planet inside the orbit of Mercury, as well as having given its name to the hypothetical vulcanoids. "Cerberus" is already the name of an asteroid, 1865 Cerberus, but the Greek form of the name, "Kerberos", was acceptable to the IAU. On 2 July 2013, the IAU announced that it formally approved the names Kerberos for P4 and Styx for P5. The names of features on the bodies in the Pluto system are related to mythology and the literature and history of exploration. In particular, the names of features on Kerberos must be related to dogs from literature, mythology, and history. The provisional designation of the satellite varies based on the source used. The

announced it as S/2011 (134340) 1, whereas the ''

'' mission website announced it as S/2011 P 1.''New Horizons'' news, Johns Hopkins University Applied Physics Laboratory
"Fourth Moon Adds to Pluto's Appeal"
, 20 July 2011

Notes

References

External links

* Showalter, Mark
NASA's Hubble Discovers Another Moon Around Pluto
20 July 2011.
Kerberos In Depth
Updated 5 December 2017. {{DEFAULTSORT:S 2011 (134340) 1 Moons of Pluto 20110720 Cerberus