5145 Pholus (/ˈfoʊləs/ FOE-ləs; from Φόλος) provisional designation 1992 AD, is an eccentric centaur in the outer Solar System, approximately 180 kilometers (110 miles) in diameter, that crosses the orbit of both Saturn and Neptune. It was discovered on 9 January 1992, by American astronomer David Rabinowitz (unaccredited) of UA's Spacewatch survey at the Kitt Peak National Observatory in Arizona, United States. The very reddish object has an elongated shape and a rotation period of 9.98 hours. It was named after the creature Pholus from Greek mythology.
(D. Rabinowitz uncredited)
|Discovery site||Kitt Peak National Obs.|
|Discovery date||9 January 1992|
|MPC designation||(5145) Pholus|
|Pronunciation||/ˈfoʊləs/ · FOE-ləs|
|centaur  · distant |
|Orbital characteristics |
|Epoch 27 April 2019 (JD 2458600.5)|
|Uncertainty parameter 1|
|Observation arc||31.74 yr (11,593 d)|
|92.09 yr (33,637 d)|
|0° 0m 38.52s / day|
|Jupiter MOID||3.469 AU|
|Dimensions||310 km × 160 km × 150 km|
|Tholen = Z |
RR (very red)
B−V = 1.19
V−R = 0.78
Pholus was the second centaur to be discovered. Centaurs are objects in between the asteroid and trans-Neptunian populations of the Solar System – that is, beyond Jupiter's and within Neptune's orbit – which behave with characteristics of both asteroids and comets.
It orbits the Sun at a distance of 8.8–32.0 AU once every 92 years and 1 month (33,637 days; semi-major axis of 20.39 AU). Its orbit has an eccentricity of 0.57 and an inclination of 25° with respect to the ecliptic. It is a Saturn-, Uranus- and Neptune-crosser, crossing the orbits of these giant planets at a mean-distance of 9.6, 11.9 and 30.1 AU from the Sun, respectively. Pholus has not come within one astronomical unit of a planet since 764 BC, and will not until 5290. It is believed that it originated in the Kuiper belt.
Pholus was discovered by David Rabinowitz (not officially credited), working with the Spacewatch program, at Kitt Peak National Observatory on 9 January 1992. Rabinowitz'es discovery was confirmed by Eugene and Carolyn Shoemaker who identified the object on images they previously took on 1 January 1992. The discovery was announced by James Scotti on 23 January 1992 in a IAU Circular (IAUC 5434) of the Central Bureau for Astronomical Telegrams. A first precovery was taken at the Australian Siding Spring Observatory in 1977, extending the centaur's observation arc by 15 years prior to its discovery. It was the second discovery of a centaur after 2060 Chiron discovered by Charles Kowal in 1977. In 1993, while with the Spacewatch program, David Rabinowitz went on to discover another centaur, 7066 Nessus.
This minor planet was named by the Minor Planet Names Committee for Pholus, a centaur from Greek mythology. As with 2060 Chiron, named after his brother Chiron, the tradition is to name this class of outer planet-crossing objects after the half-human, half-horse mythological creatures. In the mythological account, Pholus died by a self-inflicted wound from a poisoned arrow used by Heracles (see 5143 Heracles), who buried Pholus on the mountain Pholoe. The official naming citation was published by the Minor Planet Center on 14 July 1992 (M.P.C. 20523).
After its discovery, Pholus was quickly found to be very red in color, for which it has been occasionally nicknamed "Big Red". The color has been speculated to be due to organic compounds on its surface. It is classified as a Z class object on the Tholen taxonomic scheme.
The object has been classified by astronomers as RR and RR-U type, respectively. Polarimetric observations with ESO's Very Large Telescope in 2007 and 2008, revealed noticeable negative polarization at certain phase angles, distinctly different from that of trans-Neptunian objects. Pholus appears to have a rather homogeneous surface with small amount of water frost on its darker parts.
The surface composition of Pholus has been estimated from its reflectance spectrum using two spatially segregated components: dark amorphous carbon and an intimate mixture of water ice, methanol ice, olivine grains, and complex organic compounds (tholins). The carbon black component was used to match the low albedo of the object. Unlike Chiron, Pholus has shown no signs of cometary activity.
According to the Herschel Space Observatory with its PACS instrument, Nessus measures 99 kilometers in diameter and its surface has an albedo of 0.155, while a study from 1996 derived a diameter of 185 km. During 2003–2004, observations with the 1.8-meter Vatican Advanced Technology Telescope (VATT) on Mount Graham Observatory, Arizona, determined an elongated shape, 310 km × 160 km × 150 km, with a mean-diameter of 190 kilometers, based on a low albedo of 0.04. Johnston's archive lists a diameter of 107 km with an albedo of 0.126, and Collaborative Asteroid Lightcurve Link assumes a standard albedo of a carbonaceous body of 0.057 and derives a diameter of 165 km based on an absolute magnitude of 7.64.
In March 2005, a rotational lightcurve of Pholus was obtained from photometric observations by Tegler using the VATT at Mount Graham. Lightcurve analysis gave a rotation period of 9.980 hours with a brightness amplitude of 0.60 magnitude (U=3-). Alternative period determinations were also conducted by Hoffmann, Franham and Buie with concurring results of 9.977, 9.982 and 9.983 hours, respectively (U=3/3/3).
(42301) 2001 UR163, provisional designation 2001 UR163, is a resonant trans-Neptunian object and possible dwarf planet located in the outermost region of the Solar System. It was discovered on 21 October 2001 by astronomers of the Deep Ecliptic Survey program at Kitt Peak National Observatory near Tucson, Arizona, United States. The object measures approximately 600 kilometers in diameter and stays in an orbital resonance with Neptune (4:9). It has the reddest color of any object in the Solar System.(55638) 2002 VE95
(55638) 2002 VE95, also written as 2002 VE95, is a trans-Neptunian object (TNO) with an absolute magnitude of 5.7. A 2:3 orbital resonance with Neptune makes it a plutino.10199 Chariklo
10199 Chariklo ( or ; Ancient Greek: Χαρικλώ; provisional designation 1997 CU26) is the largest confirmed centaur (minor planet of the outer Solar System). It orbits the Sun between Saturn and Uranus, grazing the orbit of Uranus. On 26 March 2014, astronomers announced the discovery of two rings (nicknamed Oiapoque and Chuí) around Chariklo by observing a stellar occultation, making it the first minor planet known to have rings.Chariklo was discovered by James V. Scotti of the Spacewatch program on February 15, 1997. Chariklo is named after the nymph Chariclo (Χαρικλώ), the wife of Chiron and the daughter of Apollo.A photometric study in 2001 was unable to find a definite period of rotation. Infrared observations of Chariklo indicate the presence of water ice, which may in fact be located in its rings.Michael Brown's website lists it as possibly a dwarf planet with a measured diameter of 232 km.1748 Mauderli
1748 Mauderli, provisional designation 1966 RA, is a dark and very reddish Hildian asteroid from the outermost region of the asteroid belt, approximately 45 kilometers in diameter.
It was discovered on 7 September 1966, by astronomer Paul Wild at Zimmerwald Observatory near Bern, Switzerland, and was later named after Swiss astronomer Sigmund Mauderli.2060 Chiron
2060 Chiron (), provisional designation 1977 UB, and also known as 95P/Chiron, is a small solar system body (or minor planet) in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orbiting between the asteroid belt and the Kuiper belt.Although it was initially called an asteroid and classified only as a minor planet with the designation "2060 Chiron", it was later found to exhibit behavior typical of a comet. Today it is classified as both a minor planet and a comet, and is accordingly also known by the cometary designation "95P/Chiron".
Chiron is named after the centaur Chiron in Greek mythology.
Michael Brown lists it as possibly a dwarf planet with a measured diameter of 206 km (128 miles) which is near the lower limit for an icy dwarf planet (around 200 km, or 124 miles).5144 Achates
5144 Achates ( ə-KAY-teez), provisional designation 1991 XX, is a large Jupiter trojan from the Trojan camp, approximately 90 kilometers (56 miles) in diameter. It was discovered on 2 December 1991, by American astronomer Carolyn Shoemaker at the Palomar Observatory in southern California, United States. The assumed C-type asteroid has a rotation period of 6 hours, a notably eccentric orbit of 0.27, and belongs to the 40 largest Jupiter trojans. It was named after Achates from Greco-Roman mythology.7066 Nessus
7066 Nessus (; from Νέσσος), provisional designation 1993 HA2, is a centaur on an eccentric orbit, located beyond Saturn in the outer Solar System. It was discovered on 26 April 1993, by astronomers of the Spacewatch program at the Kitt Peak National Observatory in Arizona, United States. The dark and reddish minor planet is likely elongated and measures approximately 60 kilometers (37 miles) in diameter. It was named after Nessus from Greek mythology.8405 Asbolus
8405 Asbolus (; from Greek: Άσβολος), provisionally designated 1995 GO, is a centaur orbiting in the outer Solar System between the orbits of Jupiter and Neptune. It was discovered on 5 April 1995, by James Scotti and Robert Jedicke of Spacewatch (credited) at Kitt Peak Observatory in Arizona, United States. It is named after Asbolus, a centaur in Greek mythology and measures approximately 80 kilometers in diameter.Centaur (minor planet)
Centaurs are small Solar System bodies with a semi-major axis between those of the outer planets. They generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years, but there is one centaur, (514107) 2015 BZ509, which may be in a stable (though retrograde) orbit. Centaurs typically behave with characteristics of both asteroids and comets. They are named after the mythological centaurs that were a mixture of horse and human. It has been estimated that there are around 44,000 centaurs in the Solar System with diameters larger than 1 kilometer.The first centaur to be discovered, under the definition of the Jet Propulsion Laboratory and the one used here, was 944 Hidalgo in 1920. However, they were not recognized as a distinct population until the discovery of 2060 Chiron in 1977. The largest confirmed centaur is 10199 Chariklo, which at 260 kilometers in diameter is as big as a mid-sized main-belt asteroid, and is known to have a system of rings. It was discovered in 1997. However, the lost centaur 1995 SN55 may be somewhat larger.
No centaur has been photographed up close, although there is evidence that Saturn's moon Phoebe, imaged by the Cassini probe in 2004, may be a captured centaur that originated in the Kuiper belt. In addition, the Hubble Space Telescope has gleaned some information about the surface features of 8405 Asbolus.
As of 2008, three centaurs have been found to display comet-like comas: 2060 Chiron, 60558 Echeclus, and 166P/NEAT. Chiron and Echeclus are therefore classified as both asteroids and comets. Other centaurs, such as 52872 Okyrhoe, are suspected of having shown comas. Any centaur that is perturbed close enough to the Sun is expected to become a comet.Dale Cruikshank
Dale P. Cruikshank is an astronomer and planetary scientist in the Astrophysics Branch at NASA Ames Research Center. His research specialties are spectroscopy and radiometry of planets and small bodies in the Solar System. These small bodies include comets, asteroids, planetary satellites, dwarf planets (e.g., Pluto), and objects in the region beyond Neptune (Kuiper belt objects and trans-Neptunian bodies). He uses spectroscopic observations made with ground-based and space-based telescopes, as well as interplanetary spacecraft, to identify and study the ices, minerals, and organic materials that compose the surfaces of planets and small bodies.
Together with several colleagues, Cruikshank has found many kinds of ice on several small planetary bodies. These include frozen CH4, N2, CO, CO2, and H2O on Neptune's satellite Triton, CH4, N2, and CO on Pluto, H2O on Pluto's satellite Charon, H2O ice on many of the moons of Saturn and Uranus, H2O and CH3OH on the Centaur object 5145 Pholus. In studies with the Cassini spacecraft, he and his colleagues have found hydrocarbons on several of Saturn's satellites.David L. Rabinowitz
David Lincoln Rabinowitz (born 1960) is an American astronomer, discoverer of minor planets and researcher at Yale University.Epoch (astronomy)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time. These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane, the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit.
The main use of astronomical quantities specified in this way is to calculate other relevant parameters of motion, in order to predict future positions and velocities. The applied tools of the disciplines of celestial mechanics or its subfield orbital mechanics (for predicting orbital paths and positions for bodies in motion under the gravitational effects of other bodies) can be used to generate an ephemeris, a table of values giving the positions and velocities of astronomical objects in the sky at a given time or times.
Astronomical quantities can be specified in any of several ways, for example, as a polynomial function of the time-interval, with an epoch as a temporal point of origin (this is a common current way of using an epoch). Alternatively, the time-varying astronomical quantity can be expressed as a constant, equal to the measure that it had at the epoch, leaving its variation over time to be specified in some other way—for example, by a table, as was common during the 17th and 18th centuries.
The word epoch was often used in a different way in older astronomical literature, e.g. during the 18th century, in connection with astronomical tables. At that time, it was customary to denote as "epochs", not the standard date and time of origin for time-varying astronomical quantities, but rather the values at that date and time of those time-varying quantities themselves. In accordance with that alternative historical usage, an expression such as 'correcting the epochs' would refer to the adjustment, usually by a small amount, of the values of the tabulated astronomical quantities applicable to a fixed standard date and time of reference (and not, as might be expected from current usage, to a change from one date and time of reference to a different date and time).List of Neptune-crossing minor planets
A Neptune-crosser is a minor planet whose orbit crosses that of Neptune. The dwarf planet Pluto is the most massive example of this class of object. The known numbered Neptune-crossers (as of 2005) are:
Notes: ‡ outer-grazer
† 134340 Pluto was known at this time but not numbered
(15788) 1993 SB
(15820) 1994 TB
(15875) 1996 TP66
(19299) 1996 SZ4
(20161) 1996 TR66
(26308) 1998 SM165 ‡
28978 Ixion ‡
(29981) 1999 TD10
(32929) 1995 QY9
(33128) 1998 BU48
(33340) 1998 VG44
(44594) 1999 OX3
(47932) 2000 GN171
(54520) 2000 PJ30
(55638) 2002 VE95
(60608) 2000 EE173
(65407) 2002 RP120
(73480) 2002 PN34
(78799) 2002 XW93
(84719) 2002 VR128
(87269) 2000 OO67
(87555) 2000 QB243
(88269) 2001 KF77
(134340) Pluto †List of Saturn-crossing minor planets
A Saturn-crosser is a minor planet whose orbit crosses that of Saturn. The known numbered Saturn-crossers (as of 2005) are listed below. There is only one inner-grazer (944 Hidalgo) and no outer-grazers or co-orbitals known; most if not all of the crossers are centaurs. (15504) 1999 RG33 is a damocloid.
Notes: † inner-grazer.
944 Hidalgo †
(15504) 1999 RG33
(63252) 2001 BL41
(65407) 2002 RP120List of Uranus-crossing minor planets
A Uranus-crosser is a minor planet whose orbit crosses that of Uranus. The numbered Uranus-crossers (as of 2005) are listed below. Most, if not all, are centaurs.
Notes: † inner-grazer; ‡ outer-grazer
2060 Chiron †
10199 Chariklo †
10370 Hylonome ‡
(29981) 1999 TD10
(44594) 1999 OX3
54598 Bienor †
(65407) 2002 RP120
(73480) 2002 PN34
(87555) 2000 QB243
(88269) 2001 KF77 ‡
(95626) 2002 GZ32Pholus
Pholus may refer to:
5145 Pholus, a minor planet in the Solar System
Pholus (mythology), a centaur in Greek mythSpacewatch
The Spacewatch project is an astronomical survey that specializes in the study of minor planets, including various types of asteroids and comets at Kitt Peak National Observatory near Tucson, Arizona, in the United States.
It is led by astronomer Robert S. McMillan at the University of Arizona and was founded in 1980 by Tom Gehrels and McMillan. Spacewatch uses a 1.8-meter and a 0.9-meter dedicated telescope. In addition, it uses the Nicholas U. Mayall Telescope and the Steward Observatory's Bok Telescope for follow-up observations of near-Earth objects.The 36-inch (0.9-meter) telescope at Kitt Peak observatory has been in use by Spacewatch since 1984, and since 2000 the 72-inch Spacewatch telescope. The 36-inch telescope continued in use and was further upgraded, in particular the telescopes use electronic detectors.