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Hyperion (moon)
Encyclopedia
Hyperion also known as Saturn VII, is a moon
of Saturn
discovered by William Cranch Bond
, George Phillips Bond
and William Lassell
in 1848. It is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance. It was the first non-round
moon to be discovered.
, the Titan
god of watchfulness and observation - the elder brother of Cronus
, the Greek equivalent of Saturn - in Greek Mythology
. It is also designated Saturn VII. The adjectival form of the name is Hyperionian.
Hyperion's discovery came shortly after John Herschel
had suggested names for the seven previously-known satellites of Saturn in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope. William Lassell
, who saw Hyperion two days after William Bond
, had already endorsed Herschel's naming scheme and suggested the name Hyperion in accordance with it. He also beat Bond to publication.
) in the solar system
. The only larger moon known to be irregular in shape is Neptune's moon Proteus
. Hyperion has about 15% of the mass of Mimas
, the least massive ellipsoidal body. The largest crater
on Hyperion is approximately in diameter and deep. A possible explanation for the irregular shape is that Hyperion is a fragment of a larger body that was broken by a large impact in the distant past. A proto-Hyperion could have been from 350 to 1000 km in diameter. Over about 1,000 years, ejecta from a presumed Hyperion breakup would have impacted Titan
at low speeds building up volatiles
in the atmosphere of Titan
.
, Hyperion's low density
indicates that it is composed largely of water ice with only a small amount of rock. It is thought that Hyperion may be similar to a loosely accreted pile of rubble in its physical composition. However, unlike most of Saturn's moons, Hyperion has a low albedo
(0.2–0.3), indicating that it is covered by at least a thin layer of dark material. This may be material from Phoebe
(which is much darker) that got past Iapetus
. Hyperion is red
der than Phoebe and closely matches the color of the dark material on Iapetus.
Hyperion has a porosity
of about 0.46.
passed through the Saturn system but photographed Hyperion only from a distance. It discerned individual craters and an enormous ridge but was not able to make out the texture of the moon's surface. Early images from the Cassini
orbiter suggested an unusual appearance, but it was not until Cassinis sole targeted flyby of Hyperion on 25 September 2005 that the moon's oddness was revealed in full.
Hyperion's surface is covered with deep, sharp-edged crater
s that give it the appearance of a giant sponge. Dark material fills the bottom of each crater. The reddish substance contains long chains of carbon
and hydrogen
and appears very similar to material found on other Saturnian satellites, most notably Iapetus
.
The latest analyses of data obtained by NASA
's Cassini spacecraft during its flybys of Hyperion in 2005 and 2006 show that about 40 percent of the moon is empty space. It was suggested in July 2007 that this porosity
allows craters to remain nearly unchanged over the eons. The new analyses also confirmed that Hyperion is composed mostly of water ice with very little rock. "We find that water ice is the main constituent of the surface, but it's dirty water ice," said Dale Cruikshank, a researcher at the NASA Ames Research Center.
The Voyager 2
images and subsequent ground based photometry
indicate that Hyperion's rotation is chaotic
, that is, its axis of rotation wobbles so much that its orientation in space is unpredictable. Hyperion is the only moon in the Solar System known to rotate chaotically. It is also the only regular natural satellite
in the Solar System not to be tidally locked
.
Hyperion is unique among the large moons in that it is very irregularly shaped, has a fairly eccentric orbit, and is near a much larger moon, Titan
. These factors combine to restrict the set of conditions under which a stable rotation is possible. The 3:4 orbital resonance
between Titan and Hyperion may also make a chaotic rotation more likely. The fact that its rotation is not locked probably accounts for the relative uniformity of Hyperion's surface, in contrast to many of Saturn's other moons
which have contrasting trailing and leading hemispheres.
was a United States Navy
Crater class cargo ship
named after the moon.
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
discovered by William Cranch Bond
William Cranch Bond
William Cranch Bond was an American astronomer, and the first director of Harvard College Observatory.- Upbringing :William Cranch Bond was born in Falmouth, Maine on September 9, 1789...
, George Phillips Bond
George Phillips Bond
George Phillips Bond was an American astronomer. He was the son of William Cranch Bond. Some sources give his year of birth as 1826....
and William Lassell
William Lassell
William Lassell FRS was an English merchant and astronomer.Born in Bolton and educated in Rochdale after the death of his father, he was apprenticed from 1814 to 1821 to a merchant in Liverpool. He then made his fortune as a beer brewer, which enabled him to indulge his interest in astronomy...
in 1848. It is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance. It was the first non-round
Hydrostatic equilibrium
Hydrostatic equilibrium or hydrostatic balance is the condition in fluid mechanics where a volume of a fluid is at rest or at constant velocity. This occurs when compression due to gravity is balanced by a pressure gradient force...
moon to be discovered.
Name
The moon is named after HyperionHyperion (mythology)
Hyperion was one of the twelve Titans of Ancient Greece, the sons and daughters of Gaia and Ouranos , which were later supplanted by the Olympians. He was the brother of Cronus. He was also the lord of light, and the Titan of the east...
, the Titan
Titan (mythology)
In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age....
god of watchfulness and observation - the elder brother of Cronus
Cronus
In Greek mythology, Cronus or Kronos was the leader and the youngest of the first generation of Titans, divine descendants of Gaia, the earth, and Uranus, the sky...
, the Greek equivalent of Saturn - in Greek Mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
. It is also designated Saturn VII. The adjectival form of the name is Hyperionian.
Hyperion's discovery came shortly after John Herschel
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
had suggested names for the seven previously-known satellites of Saturn in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope. William Lassell
William Lassell
William Lassell FRS was an English merchant and astronomer.Born in Bolton and educated in Rochdale after the death of his father, he was apprenticed from 1814 to 1821 to a merchant in Liverpool. He then made his fortune as a beer brewer, which enabled him to indulge his interest in astronomy...
, who saw Hyperion two days after William Bond
William Cranch Bond
William Cranch Bond was an American astronomer, and the first director of Harvard College Observatory.- Upbringing :William Cranch Bond was born in Falmouth, Maine on September 9, 1789...
, had already endorsed Herschel's naming scheme and suggested the name Hyperion in accordance with it. He also beat Bond to publication.
Shape
Hyperion is one of the largest bodies known to be highly irregularly shaped (non-ellipsoidal; i.e., not in hydrostatic equilibriumHydrostatic equilibrium
Hydrostatic equilibrium or hydrostatic balance is the condition in fluid mechanics where a volume of a fluid is at rest or at constant velocity. This occurs when compression due to gravity is balanced by a pressure gradient force...
) in the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. The only larger moon known to be irregular in shape is Neptune's moon Proteus
Proteus (moon)
Proteus , also known as Neptune VIII, is the second largest Neptunian moon, and Neptune's largest inner satellite. Discovered by Voyager 2 spacecraft in 1989, it is named after Proteus, the shape-changing sea god of Greek mythology...
. Hyperion has about 15% of the mass of Mimas
Mimas (moon)
Mimas is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I....
, the least massive ellipsoidal body. The largest crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
on Hyperion is approximately in diameter and deep. A possible explanation for the irregular shape is that Hyperion is a fragment of a larger body that was broken by a large impact in the distant past. A proto-Hyperion could have been from 350 to 1000 km in diameter. Over about 1,000 years, ejecta from a presumed Hyperion breakup would have impacted Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
at low speeds building up volatiles
Volatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
in the atmosphere of Titan
Atmosphere of Titan
The atmosphere of Titan is known as the only fully developed atmosphere that exists on a natural satellite in our solar system.-History:The presence of a significant atmosphere was first suspected by Spanish astronomer Josep Comas Solà, who observed distinct limb darkening on Titan in 1903, and...
.
Composition
Like most of Saturn's moonsSaturn's natural satellites
The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometre across, to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, fifty-three of which have names, and only thirteen of which have diameters larger than 50...
, Hyperion's low density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
indicates that it is composed largely of water ice with only a small amount of rock. It is thought that Hyperion may be similar to a loosely accreted pile of rubble in its physical composition. However, unlike most of Saturn's moons, Hyperion has a low albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
(0.2–0.3), indicating that it is covered by at least a thin layer of dark material. This may be material from Phoebe
Phoebe (moon)
Phoebe is an irregular satellite of Saturn. It was discovered by William Henry Pickering on 17 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart...
(which is much darker) that got past Iapetus
Iapetus (moon)
Iapetus ), occasionally Japetus , is the third-largest moon of Saturn, and eleventh in the Solar System. It was discovered by Giovanni Domenico Cassini in 1671...
. Hyperion is red
Red
Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
der than Phoebe and closely matches the color of the dark material on Iapetus.
Hyperion has a porosity
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
of about 0.46.
Surface features
Voyager 2Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...
passed through the Saturn system but photographed Hyperion only from a distance. It discerned individual craters and an enormous ridge but was not able to make out the texture of the moon's surface. Early images from the Cassini
Cassini-Huygens
Cassini–Huygens is a joint NASA/ESA/ASI spacecraft mission studying the planet Saturn and its many natural satellites since 2004. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan, although it has also returned...
orbiter suggested an unusual appearance, but it was not until Cassinis sole targeted flyby of Hyperion on 25 September 2005 that the moon's oddness was revealed in full.
Hyperion's surface is covered with deep, sharp-edged crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s that give it the appearance of a giant sponge. Dark material fills the bottom of each crater. The reddish substance contains long chains of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and appears very similar to material found on other Saturnian satellites, most notably Iapetus
Iapetus (moon)
Iapetus ), occasionally Japetus , is the third-largest moon of Saturn, and eleventh in the Solar System. It was discovered by Giovanni Domenico Cassini in 1671...
.
The latest analyses of data obtained by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Cassini spacecraft during its flybys of Hyperion in 2005 and 2006 show that about 40 percent of the moon is empty space. It was suggested in July 2007 that this porosity
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
allows craters to remain nearly unchanged over the eons. The new analyses also confirmed that Hyperion is composed mostly of water ice with very little rock. "We find that water ice is the main constituent of the surface, but it's dirty water ice," said Dale Cruikshank, a researcher at the NASA Ames Research Center.
Rotation
Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...
images and subsequent ground based photometry
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...
indicate that Hyperion's rotation is chaotic
Chaos theory
Chaos theory is a field of study in mathematics, with applications in several disciplines including physics, economics, biology, and philosophy. Chaos theory studies the behavior of dynamical systems that are highly sensitive to initial conditions, an effect which is popularly referred to as the...
, that is, its axis of rotation wobbles so much that its orientation in space is unpredictable. Hyperion is the only moon in the Solar System known to rotate chaotically. It is also the only regular natural satellite
Regular moon
In astronomy, a regular moon is a natural satellite following a relatively close and generally prograde orbit with little orbital inclination or eccentricity...
in the Solar System not to be tidally locked
Tidal locking
Tidal locking occurs when the gravitational gradient makes one side of an astronomical body always face another; for example, the same side of the Earth's Moon always faces the Earth. A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner...
.
Hyperion is unique among the large moons in that it is very irregularly shaped, has a fairly eccentric orbit, and is near a much larger moon, Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
. These factors combine to restrict the set of conditions under which a stable rotation is possible. The 3:4 orbital resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
between Titan and Hyperion may also make a chaotic rotation more likely. The fact that its rotation is not locked probably accounts for the relative uniformity of Hyperion's surface, in contrast to many of Saturn's other moons
Saturn's natural satellites
The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometre across, to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, fifty-three of which have names, and only thirteen of which have diameters larger than 50...
which have contrasting trailing and leading hemispheres.
Exploration
Hyperion has been imaged several times from moderate distances by the Cassini orbiter. The first close targeted fly-by occurred at a distance of 500 kilometres (310.7 mi) on 26 September 2005. Cassini made another close approach to Hyperion on 25 August 2011. Cassini's next flyby will occur on 16 September 2011, when it passes at 58000 kilometres (36,039.6 mi).Namesakes
USS Hyperion (AK-107)USS Hyperion (AK-107)
USS Hyperion , a Crater-class cargo ship, is the only ship of the United States Navy to have this name.Hyperion, formerly Liberty ship SS Christopher C. Andrews, was launched 24 June 1943 by Permanente Metals Corp., Richmond, California; sponsored by Mrs. Percy Lindt; acquired by the Navy from WSA...
was a United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
Crater class cargo ship
Crater class cargo ship
Crater-class cargo ship is a category of freighter that was constructed for use by the United States Navy during World War II under Maritime Commission EC2-S-C1 type....
named after the moon.
External links
- Cassini mission Hyperion page
- Hyperion Profile at NASA's Solar System Exploration site
- The Planetary Society: Hyperion
- NASA: Saturn's Hyperion, A Moon With Odd Craters
- Cassini images of Hyperion
- Images of Hyperion at JPL's Planetary Photojournal
- Hyperion nomenclature from the USGS planetary nomenclature page