Styx, formal designation (134340) Pluto V, is a small natural satellite of Pluto whose discovery was announced on 11 July 2012. It was discovered by use of 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 ...

, and is the smallest of the five known moons 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 ...

. It was imaged along with Pluto and Pluto's 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, albeit poorly with only a single image of Styx obtained. Styx is the second-closest known satellite to Pluto, and the fifth discovered. It was discovered one year after Kerberos. Styx is approximately across its longest dimension, and its orbital period is 20.1 days.

Discovery and observations

Styx was discovered by a team led by astronomer Mark R. Showalter, using fourteen sets of images taken between 26 June and 9 July 2012 by the Wide Field Camera 3 fitted to the Hubble. The discovery was announced on 11 July 2012. Styx is about half as bright as the dimmest previously known object in the system, Kerberos, and about one hundred thousandth as bright as Pluto. It was designated S/2012 (134340) 1, and informally referred to as P5. The survey work leading to the discovery of Styx was in preparation for the mission of the uncrewed ''

'' spacecraft, which flew by the Pluto system on 14 July 2015. The discovery of another small Plutonian moon heightened concerns that this region of space may harbor more bodies too small to be detected, and that the spacecraft could be damaged by an uncharted body or planetary ring as it traversed the system at a speed of over 13 km/s. Tiny moons, such as Saturn's moon Pallene, tend to be associated with tenuous rings or arcs, because their gravity is unable to hold on to material ejected by

meteoroid A meteoroid ( ) is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than ''asteroids'', ranging in size from grains to objects up to wide. Objects smaller than meteoroids are classifie ...

impacts and such diffuse material represents the chief navigational hazard. However, the ''New Horizons'' spacecraft did not detect any smaller moons or rings and it passed through the Pluto system safely.

Origin

The unexpectedly complex moon system around Pluto may be the result of a collision between Pluto and another sizable

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 in the distant past. Pluto's moons may have coalesced from the debris from such an event, similar to the early giant impact thought to have created the Earth's

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 ...

. The orbital resonances may have acted as "ruts" to gather material from the collision.

Physical characteristics

Styx was originally estimated to have a diameter of between . These figures were inferred from the

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of Styx and by using an estimated

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 ...

of 0.35 and 0.04 for the lower and upper bounds, respectively. Measurements made by ''New Horizons'' found an elongated shape with dimensions measuring approximately . It is thought to have formed from the debris lofted by a collision, which would have led to losses of the more volatile ices, such as those of

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

and

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

, in the composition of the impactors. This process is expected to have created a body consisting mainly of

water ice Water ice may refer to: *Ice formed by water (as opposed to other substances) *In ice climbing, ice made from flowing water (as opposed to ice from precipitation) *The alternate term for various similar frozen fruit-flavoured desserts: ** Italian ic ...

Orbit

Styx orbits the Pluto–Charon

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 ...

at a distance of 42,656 km, putting it between the orbits of Charon and Nix. All of Pluto's moons appear to travel in orbits that are very nearly circular and coplanar, described by Styx's discoverer Mark Showalter as "neatly nested ... a bit like Russian dolls". It is in an 11:6

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 Hydra, and an 11:9 resonance with Nix (the ratios represent numbers of orbits completed per unit time; the period ratios are the inverses). As a result of this "Laplace-like" 3-body resonance, it has conjunctions with Nix and Hydra in a 2:5 ratio. Its orbital period of 20.16155 days is about 5.0% from a 1:3 mean-motion resonance with the Charon–Pluto orbital period of 6.387 days. With the other moons Nix, Kerberos, and Hydra, it forms part of an unusual 1:3:4:5:6 (period ratio) sequence of near resonances. In contrast to the orbit, Stygian rotation is chaotic; like the other small Plutonian moons, Styx is not tidally locked, and its rotation varies over short timescales (at a rate of about 3.239 days at the time of the ''New Horizons'' flyby).

Naming

Before any of Pluto's moons were discovered, author

Edmond Hamilton Edmond Moore Hamilton (October 21, 1904 – February 1, 1977) was an American writer of science fiction during the mid-twentieth century. He is known for writing most of the Captain Future stories. Early life Born in Youngstown, Ohio, he ...

referred to three moons of Pluto in his 1940

science fiction Science fiction (often shortened to sci-fi or abbreviated SF) is a genre of speculative fiction that deals with imaginative and futuristic concepts. These concepts may include information technology and robotics, biological manipulations, space ...

novel ''Calling Captain Future'', naming them , , and . Upon discovery, Styx received the minor planet designation S/2012 (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 2012. It is known informally as "P5", meaning the fifth Plutonian moon to be discovered. The designation S/2012 P 1 has sometimes been used, following the pre-2006 format where Pluto was still considered a planet and given its own single-letter abbreviation. 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 plays 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, but also alluding to the fictional planets of Vulcan and

in the ''Star Trek'' universe. The 'Romulus' suggestion was discounted, as 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 same name in 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 figure and had already been used for a hypothetical planet inside the orbit of Mercury, as well as having given its name to the

vulcanoid The vulcanoids are a hypothetical population of asteroids that orbit the Sun in a dynamically stable zone inside the orbit of the planet Mercury. They are named after the hypothetical planet Vulcan, which was proposed on the basis of irregulari ...

s. On 2 July 2013, the IAU announced that it had formally approved the names ''

'' for P5 and ''Kerberos'' for P4.

References

External links

* Showalter, Mark
Hubble Press Release: Hubble Discovers a Fifth Moon Orbiting Pluto
11 July 2012. * ZME Scienc
New moon discovered around Pluto – the fifth
11 July 2012. {{DEFAULTSORT:S 2012 (134340) 1 20120626 Discoveries by the Hubble Space Telescope Moons of Pluto Moons with a prograde orbit