617 Patroclus
Encyclopedia
617 Patroclus is a binary
minor planet
made up of two similarly-sized objects orbiting their common centre of gravity. It is a Trojan asteroid, sharing an orbit with Jupiter
. It was discovered in 1906 by August Kopff
, and was the second trojan to be discovered. Its binary nature was discovered in 2001; the name Patroclus now refers to the larger of the two components, while its slightly smaller companion body has been named Menoetius (m , official designation (617) Patroclus I Menoetius). Recent evidence suggests that the objects are icy comet
s, rather than rocky asteroid
s.
, , in an orbit called the 'Trojan node' after one of the sides in the legendary Trojan War
(the other node, at the , is called the 'Greek node'). Patroclus is the only object in the Trojan camp to be named after a Greek character
; the naming conventions for the trojan asteroids were not adopted until after Patroclus was named (similarly, the asteroid Hektor
is the only Trojan character to appear in the Greek camp).
object, made up of two components of roughly similar size. In February, 2006, a team of astronomers led by Franck Marchis
measured accurately the orbit of the system using the Keck
Laser guide star
adaptive optics
system. They estimated that the two components orbit around their center of mass
in 4.283±0.004 d
at a distance of 680±20 km, describing a roughly circular orbit. Combining their observations with thermal measurements taken in November 2000, the team estimated the size of the components of the system. The slightly larger component, which measures 122 km in diameter, retains the name Patroclus. The smaller component, measuring 112 km, is now named Menoetius, after the legendary Patroclus's father. Its provisional designation was S/2001 (617) 1.
s, is more similar to a comet
in composition. It is suspected that many Trojan asteroids are in fact small planetesimal
s captured in the Lagrange point of Jupiter–Sun system during the outer migration of the giant planet
s, 3.9 billion years ago. This scenario was proposed by A. Morbidelli and colleagues in a series of articles published in May 2005 in Nature
journal.
Binary asteroid
A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993...
minor planet
Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...
made up of two similarly-sized objects orbiting their common centre of gravity. It is a Trojan asteroid, sharing an orbit with Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. It was discovered in 1906 by August Kopff
August Kopff
August Kopff was a German astronomer who discovered several comets and asteroids. He worked in Heidelberg, then joined the Humboldt University of Berlin where he became the Director of the Institute for Astronomical Calculation.He discovered some comets, including periodic comet 22P/Kopff and the...
, and was the second trojan to be discovered. Its binary nature was discovered in 2001; the name Patroclus now refers to the larger of the two components, while its slightly smaller companion body has been named Menoetius (m , official designation (617) Patroclus I Menoetius). Recent evidence suggests that the objects are icy comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s, rather than rocky asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s.
Orbit
Patroclus orbits in Jupiter's trailing Lagrangian pointLagrangian point
The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
, , in an orbit called the 'Trojan node' after one of the sides in the legendary Trojan War
Trojan War
In Greek mythology, the Trojan War was waged against the city of Troy by the Achaeans after Paris of Troy took Helen from her husband Menelaus, the king of Sparta. The war is among the most important events in Greek mythology and was narrated in many works of Greek literature, including the Iliad...
(the other node, at the , is called the 'Greek node'). Patroclus is the only object in the Trojan camp to be named after a Greek character
Patroclus
In Greek mythology, as recorded in the Iliad by Homer, Patroclus, or Patroklos , was the son of Menoetius, grandson of Actor, King of Opus, and was Achilles' beloved comrade and brother-in-arms....
; the naming conventions for the trojan asteroids were not adopted until after Patroclus was named (similarly, the asteroid Hektor
624 Hektor
624 Hektor is the largest Jupiter Trojan. It was discovered in 1907 by August Kopff.Hektor is a D-type asteroid, dark and reddish in colour. It lies in Jupiter's leading Lagrangian point, , called the 'Greek' node after one of the two sides in the legendary Trojan War...
is the only Trojan character to appear in the Greek camp).
Binary system
In 2001, it was discovered that Patroclus is a binaryBinary asteroid
A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993...
object, made up of two components of roughly similar size. In February, 2006, a team of astronomers led by Franck Marchis
Franck Marchis
Franck Marchis , astronomer and planetary scientist, is best known for his discovery and characterization of multiple asteroids and its study of Io volcanism.The asteroid 6639 Marchis was named in his honor on April 4, 2007....
measured accurately the orbit of the system using the Keck
Keck telescopes
The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of near the summit of Mauna Kea in Hawai'i. The primary mirrors of each of the two telescopes are in diameter, making them the second largest optical telescopes in the world, slightly behind the Gran Telescopio...
Laser guide star
Laser guide star
Laser guide stars are a form of artificial star created for use in astronomical adaptive optics imaging.Adaptive optics systems require a wavefront reference source in order to correct atmospheric distortion of light...
adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
system. They estimated that the two components orbit around their center of mass
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
in 4.283±0.004 d
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
at a distance of 680±20 km, describing a roughly circular orbit. Combining their observations with thermal measurements taken in November 2000, the team estimated the size of the components of the system. The slightly larger component, which measures 122 km in diameter, retains the name Patroclus. The smaller component, measuring 112 km, is now named Menoetius, after the legendary Patroclus's father. Its provisional designation was S/2001 (617) 1.
Composition
Because of the density of the components (0.8 g/cm³) is less than water and about one third that of rock, the team of researchers led by F. Marchis suggest that the Patroclus system, previously thought to be a pair of rocky asteroidAsteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, is more similar to a comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
in composition. It is suspected that many Trojan asteroids are in fact small planetesimal
Planetesimal
Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger...
s captured in the Lagrange point of Jupiter–Sun system during the outer migration of the giant planet
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
s, 3.9 billion years ago. This scenario was proposed by A. Morbidelli and colleagues in a series of articles published in May 2005 in Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
journal.