For other meanings see Phoebe. Phoebe from Sesame Street In Greek mythology, Phoebe referred to several people. ...

Phoebe

Discovery
Discovered by	W.H. Pickering
Discovered in	March 17, 1899 / August 16, 1898
Orbital characteristics [1]
Semimajor axis	12,955,759 km
Eccentricity	0.1562415
Orbital period	550.564636 d
Inclination	151.66° (to Saturn's equator) [2]
Is a satellite of	Saturn
Physical characteristics
Diameter	230 x 220 x 210 km
Mass	7.2×1018 kg
Mean density	2.3 g/cm3
Surface gravity	0.039 m/s2
Rotation period	0.38675 d (9 h 16 min 55.2 s) [3]
Axial tilt	17.4° [4]
Albedo	0.06
Atmosphere	none

Phoebe (fee'-bee, Greek Φοίβη) is a moon of Saturn. It was discovered by William Henry Pickering on March 17, 1899 from photographic plates that had been taken starting on August 16, 1898 at Arequipa, Peru by DeLisle Stewart. It was the first satellite to be discovered photographically. Download high resolution version (565x823, 63 KB)Phoebe, as imaged by the Cassini probe on June 11, 2004 JPL image reference: PIA06064. ... William Henry Pickering (February 15, 1858 – January 17, 1938) was an American astronomer, brother of Edward Charles Pickering. ... Jump to: navigation, search March 17 is the 76th day of the year in the Gregorian Calendar (77th in Leap years). ... Jump to: navigation, search 1899 was a common year starting on Sunday (see link for calendar). ... Jump to: navigation, search August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... Jump to: navigation, search 1898 was a common year starting on Saturday (see link for calendar). ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... In geometry, the semi-major axis (also semimajor axis) a applies to ellipses and hyperbolas. ... A kilometre (American spelling: kilometer) (symbol: km) is a unit of length equal to 1000 metres (from the Greek words khilia = thousand and metro = count/measure). ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... Moons of solar system scaled to Earths Moon The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... For the geometric term, see diameter. ... Jump to: navigation, search Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... Jump to: navigation, search The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... Jump to: navigation, search Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Jump to: navigation, search It has been suggested that Gravitational constant be merged into this article or section. ... Jump to: navigation, search Acceleration is the time rate of change of velocity, and at any point on a v-t graph, it is given by the gradient of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of... Jump to: navigation, search On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... Axial tilt is an astronomical term regarding the inclination angle of a planets rotational axis in relation to its orbital plane. ... Jump to: navigation, search The albedo is a measure of reflectivity of a surface or body. ... Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ... Moons of solar system scaled to Earths Moon The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... William Henry Pickering (February 15, 1858 – January 17, 1938) was an American astronomer, brother of Edward Charles Pickering. ... Jump to: navigation, search March 17 is the 76th day of the year in the Gregorian Calendar (77th in Leap years). ... Jump to: navigation, search 1899 was a common year starting on Sunday (see link for calendar). ... Jump to: navigation, search August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... Jump to: navigation, search 1898 was a common year starting on Saturday (see link for calendar). ... Jump to: navigation, search Arequipa is a city in southern Peru and the nations second-largest city. ... DeLisle Stewart (March 16, 1870 – February 2, 1941) was an American astronomer. ...

Name

The moon is named after Phoebe, a Titan in Greek mythology. It is also designated Saturn IX. The IAU nomenclature standards have stated that features on Phoebe are to be named after characters in the Greek myth of Jason and the Argonauts. In 2005, the IAU officially named 24 craters (Acastus, Admetus, Amphion, Butes, Calais, Canthus, Clytius, Erginus, Euphemus, Eurydamas, Eurytion, Eurytus, Hylas, Idmon, Iphitus, Jason, Mopsus, Nauplius, Oileus, Peleus, Phlias, Talaus, Telamon, and Zetes). Jump to: navigation, search Phoebe, a Titan traditionally associated with the moon. ... In Greek mythology, the Titans (Greek Τιταν, plural Τιτανες) are among a series of gods, some of whom opposed Zeus and the Olympian gods in their ascent to power. ... Jump to: navigation, search Greek mythology comprises the collected narratives of Greek gods, goddesses, heroes, and heroines, originally created and spread within an oral-poetic tradition. ... Jump to: navigation, search Logo of the IAU The International Astronomical Union (IAU) unites national astronomical societies from around the world. ... Planetary nomenclature, like terrestrial nomenclature, is used to uniquely identify a feature on the surface of a planet or natural satellite so that the feature can be easily located, described, and discussed. ... Jump to: navigation, search Jason (Greek: Ίασων, Etruscan: Easun) is a hero of Greek mythology. ... See also: Other events of 2005 List of years in science . ...

Dr. Toby Owen of the University of Hawaii at Manoa, chairman of the International Astronomical Union Outer Solar System Task Group said Jean Charlots mural called Commencement is featured at Bachman Hall, the administrative center of the University of Hawai`i System. ...

"We picked the legend of the Argonauts for Phoebe as it has some resonance with the exploration of the Saturn system by Cassini-Huygens. We can't say that our participating scientists include heroes like Hercules and Atalanta, but they do represent a wide, international spectrum of outstanding people who were willing to take the risk of joining this voyage to a distant realm in hopes of bringing back a grand prize."

Orbital characteristics

For more than 100 years, Phoebe was Saturn's outermost known moon, until the discovery of several smaller moons in 2000. Phoebe is almost 4 times more distant from Saturn than its nearest major neighbor (Iapetus), and is substantially larger than any of the other moons orbiting planets at comparable distances. Jump to: navigation, search This article is about the year 2000. ... Iapetus (eye-ap-i-tus, Greek Ιαπετός) (British spelling: Japetus) is the third-largest moon of Saturn (see: Saturns natural satellites), discovered by Giovanni Domenico Cassini in 1671. ...

All of Saturn's moons up to Iapetus orbit very nearly in the plane of Saturn's equator. The outer moons can be broken down into two groups: Siarnaq's group (Kiviuq, Ijiraq, Paaliaq, Albiorix, Erriapo, Siarnaq and Tarvos) is inclined 33.5-46.5° whilst Phoebe's group (Phoebe, Skathi, Narvi, Mundilfari, Suttungr, Thrymr and Ymir) is retrograde and inclined 134.5-175.5°. Both groups are fairly to highly eccentric, and none of their moons are expected to rotate synchronously as all the inner moons of Saturn do (except for Hyperion). The inclinations given are with respect to the solar system's ecliptic rather than Saturn's equator, as the local Laplace plane at these distances is already quite tilted with respect to Saturn's equator. This tilt reaches 15° at Iapetus' distance; at Phoebe's, it has already merged with the ecliptic (tilt of 26°). In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... Siarnaq (see-ar-naak) (Saturn XXIX) is a natural satellite of Saturn. ... Kiviuq (kee-vee-oek or kiv-ee-uk) is a natural satellite of Saturn. ... Ijiraq (ee-ye-raak or ee-ji-raak) is a natural satellite of Saturn. ... Paaliaq (paw-lee-aak) is a natural satellite of Saturn. ... Albiorix (al-bee-or-iks) is a natural satellite of Saturn. ... Erriapo (air-ee-ap-oe?, Latin Erriapō or Erriappō) (Saturn XXVIII) is a natural satellite of Saturn. ... Tarvos (tar-vus) (Saturn XXI) is a natural satellite of Saturn. ... Skathi (skaadh-ee, with a voiced th as in this) (Saturn XXVII) is a natural satellite of Saturn. ... Narvi (nar-vee) (Saturn XXXI) is a natural satellite of Saturn. ... Mundilfari (moon-dil-fair-ee, Norse Mundilfäri) (Saturn XXV) is a natural satellite of Saturn. ... Suttungr (soot-oong-ur) (Saturn XXIII) is a natural satellite of Saturn. ... Thrymr (THRIM er) is a natural satellite of Saturn. ... Ymir (ee-mur) (Saturn XIX) is a natural satellite of Saturn. ... This article is about retrograde motion. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... Hyperion (hye-peer-ee-un, Greek ‘Υπερίων) is a moon of Saturn discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. ... Jump to: navigation, search Presentation of the solar system (not to scale) The solar system is the retinue of objects gravitationally bound to our Sun. ... The Laplace plane is defined as the mean plane occupied by the orbit of a satellite during a precession cycle. ...

Physical characteristics

Closeup image of Phoebe from the Cassini-Huygens spacecraft, June 13, 2004.

Phoebe is roughly spherical and has a diameter of 220 kilometres (about 137 miles), which is equal to about one-fifteenth of the diameter of Earth's moon. Phoebe rotates on its axis every nine hours and it completes a full orbit around Saturn in about 18 months. Its surface temperature is only 75 K (-198°C). Jump to: navigation, search Image File history File links Phoebe6. ... Jump to: navigation, search Image File history File links Phoebe6. ... This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver, just after the main engine has begun firing. ... Jump to: navigation, search June 13 is the 164th day of the year in the Gregorian calendar (165th in leap years), with 201 days remaining. ... Jump to: navigation, search 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ...

Most of Saturn's inner moons have very bright surfaces, but Phoebe's albedo is very low (0.06), as dark as lamp black. The Phoebean surface is extremely heavily scarred, with craters up to 80 kilometres across, one of which has walls 16 kilometres high. Jump to: navigation, search The albedo is a measure of reflectivity of a surface or body. ...

Phoebe's dark colouring initially led to scientists surmising that it was a captured asteroid, as it resembled the common class of dark carbonaceous asteroids. These are chemically very primitive and are thought to be composed of original solids that condensed out of the solar nebula with little modification since then. Jump to: navigation, search An asteroid is a small, solid object in our Solar System, orbiting the Sun. ... C-type asteroids are carbonaceous asteroids. ... In cosmogony, the solar nebula is the gaseous cloud (or accretion disc) from which our solar system is believed to have formed. ...

However, images from the Cassini-Huygens space probe indicate that Phoebe's craters show a considerable variation in brightness, which indicate the presence of large quantities of ice below a relatively thin blanket of dark surface deposits some 300 to 500 metres (980 to 1,600 feet) thick. In addition, quantities of carbon dioxide have been detected on the surface, a finding which has never been replicated on an asteroid. It is estimated that Phoebe is about 50% rock, as opposed to the 35% or so that typifies Saturn's inner moons. For these reasons, scientists are coming to believe that Phoebe is in fact a captured Centaur, one of a number of icy planetoids from the Kuiper belt that orbit the Sun between Jupiter and Neptune. [5] Phoebe is the first such object to be imaged as anything other than a dot. This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver, just after the main engine has begun firing. ... The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs. ... Planetoid (meaning planet-like) is an old synonym of asteroid. ... Artists rendering of the Kuiper Belt and more distant Oort cloud. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... Jump to: navigation, search The Sun is the star at the centre of our Solar system. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ...

Material displaced from Phoebe's surface by microscopic meteor impacts may be responsible for the dark surfaces of Hyperion and the leading hemisphere of Iapetus. Debris from the biggest impacts may have been the building blocks of the other moons of Phoebe's group—all of which are less than 10 km in diameter.

Spacecraft flybys

Closeup image of Phoebe from Cassini-Huygens

The Voyager 2 spacecraft passed by Phoebe in September 1981, although the 2.2 Gm (2.2 million kilometres) distance and low resolution meant that relatively little could be learned from the resulting images. Download high resolution version (565x799, 205 KB)NASA closeup image of Saturn moon Phoebe by the Cassini spacecraft JPL image reference: PIA06073. ... Download high resolution version (565x799, 205 KB)NASA closeup image of Saturn moon Phoebe by the Cassini spacecraft JPL image reference: PIA06073. ... The Voyager 2 spacecraft was launched in 1977. ... Jump to: navigation, search 1981 (MCMLXXXI)is a common year starting on Thursday of the Gregorian calendar. ...

The Cassini spacecraft flew within 2,068 kilometers (about 1,285 miles) of Phoebe on June 11, 2004, returning many high-resolution images of the moon and its scarred surface. This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver, just after the main engine has begun firing. ... Jump to: navigation, search June 11 is the 162nd day of the year in the Gregorian Calendar (163rd in leap years), with 203 days remaining. ... Jump to: navigation, search 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ...

See also

• List of geological features on Saturn's smaller moons

This is list of named geological features on Janus, Epimetheus and Phoebe. ...

External links

• Harvard College Observatory Bulletin, 49 (1899) 1
• Astronomical Journal, 20 (1899) 13
• Astrophysical Journal, 9 (1899) 274
• Astronomische Nachrichten, 149 (1899) 189/190 (same as above)
• The Observatory, 22 (1899) 158
• Small Moons of Saturn - Cassini images of Phoebe and other Saturnian moons
• Cassini pass reveals moon secrets - BBC, 14 June 2004
• The Planetary Society: Phoebe
• Phoebe feature names
• Wired: Saturn's Odd Moon Out (2005)

Jump to: navigation, search June 14 is the 165th day of the year in the Gregorian calendar (166th in leap years), with 200 days remaining. ... Jump to: navigation, search 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ...

Ijiraq (ee-ye-raak or ee-ji-raak) is a natural satellite of Saturn. ... Paaliaq (paw-lee-aak) is a natural satellite of Saturn. ...