 Hubble Space Telescope image composite of Patroclus and its companion Menoetius, taken in 2018 | |
| Discovery[1] | |
|---|---|
| Discovered by | A. Kopff |
| Discovery site | Heidelberg Obs. |
| Discovery date | 17 October 1906 |
| Designations | |
| (617) Patroclus | |
| Pronunciation | /pəˈtroʊkləs/[2] |
Named after | ΠάτροκλοςPatroklos (Greek mythology)[3] |
| 1906 VY · 1941 XC 1962 NB | |
| Jupiter trojan[1][4][5] Trojan[6][7] · background[7] | |
| Adjectives | Patroclean/pætrəˈkliːən/[8] |
| Orbital characteristics[4] | |
| Epoch 25 February 2023 (JD 2460000.5) | |
| Uncertainty parameter 0 | |
| Aphelion | 5.937AU |
| Perihelion | 4.480 AU |
| 5.209 AU | |
| Eccentricity | 0.1399 |
| 11.89 yr (4,342 d) | |
| 319.506° | |
| 0° 4m 58.464s / day | |
| Inclination | 22.062° |
| 44.360° | |
| 308.306° | |
| Knownsatellites | 1 (Menoetius)[9] |
| Jupiter MOID | 0.1868 AU |
| TJupiter | 2.835 |
| Physical characteristics | |
| Dimensions | 127 km × 117 km × 98 km(primary only)[10] |
| 113±3 km(primary only)[10] 140.36±0.87 km[11] 140.85±3.37 km[12] 140.92±4.7 km[13] 143.14±8.37 km[14] 154 km[10] | |
| Volume | 1.36×106 km3[10] |
| Mass | (1.36±0.11)×1018 kg[14] 1.20×1018 kg[10] |
Meandensity | 0.88±0.17 g/cm3[14][10] |
| 102.8 h[15] 102 h[16] 103.02±0.40 h[17] 103.5±0.3 h[18] | |
| 0.047±0.003[11][12][13] | |
| D(Tholen)[19] C0(Barucci)[19] D(Tedesco)[19] U–B =0.215±0.045[19] B–V =0.710±0.050[20] V–R =0.420±0.030[20] V–I =0.830±0.020[20] | |
| 8.18[4][11][12][13][5] | |
617 Patroclus (/pəˈtroʊkləs/pə-TROH-kləs) is a large binaryJupiter trojan asteroid. It is a darkD-type asteroid and aslow rotator, due to the 103-hour orbital period of its two components. It is one of five Jupiter trojan asteroids targeted by theLucy space probe, and is scheduled for aflyby in 2033.
Patroclus was discovered on 17 October 1906, by astronomerAugust Kopff at theHeidelberg Observatory in Germany, and was named afterPatroclus in Greek mythology.[1] It was the second trojan to be discovered and the only member of theTrojan camp named after a Greek figure, as the convention of naming one 'camp' after Greek figures of the Trojan War and the other after Trojan figures had not yet been established.[3]
Patroclus was long thought to be one of thelargest Jupiter trojans, with a diameter on the order of 150 km. However, in 2001 it was discovered to be abinary asteroid of two similarly sized objects. The namePatroclus is now assigned to the larger component, some 110–115 km in diameter, while the secondary, slightly smaller at 100–105 km in diameter, has been named Menoetius (/mɪˈniːʃəs/mə-NEE-shəs).[a] This was the first discovery of a binary trojan asteroid.[9]
Patroclus orbits in Jupiter's trailingLagrangian point,L5,[9] in an area called theTrojan camp after one of the sides in the legendaryTrojan War (the other node, at theL4 point, is called the "Greek camp").
It orbits the Sun at a distance of 4.5–5.9 AU once every 11 years and 11 months (4,353 days). Its orbit has aneccentricity of 0.14 and aninclination of 22° with respect to theecliptic.[4] The asteroid'sobservation arc begins at the discovering Heidelberg Observatory in November 1906, about 3 weeks after its official discovery observation.[1]
 Plot of the results of the multi-chord stellar occultation by 617 Patroclus and Menoetius | |
| Discovery | |
|---|---|
| Discovery date | 2001 |
| Designations | |
| Pronunciation | /mɪˈniːʃəs/ |
Named after | Menoetius(Greek mythology) |
| Adjectives | Menoetian/mɪˈniːʃən/[21]) |
| Orbital characteristics | |
| 680±20 km[9] 664.6 km[10] | |
| 102.8 h | |
| Satellite of | Patroclus |
| Physical characteristics | |
| Dimensions | 117 km × 108 km × 90 km[10] |
| 104±3 km[10] | |
In 2001, it was discovered that Patroclus is abinary system, made up of two components of roughly similar size.[9][22][23] It is one of six Trojan asteroidsbelieved to be binary. In 2006, accurate measurements of the orbit from theKeckLaser guide staradaptive optics system were reported.[24]
It was estimated[25] that the two components orbit around theircenter of mass in4.283±0.004 days at a distance of680±20 km in a roughly circular orbit.[9] Combining these observations with thermal measurements taken in 2000, the sizes of the components of the system were estimated at 106 km and 98 km, with an equivalent whole-system diameter of 145 km,[9] refined by later measurements from the Keck Observatory to approximately 122 km and 112 km for each partner,[26] and a co-orbital period of103.5±0.3 hours (4.3125±0.0125 days).[24][18]
On 21 October 2013, both bodiesocculted amagnitude 8.8 star as observed by a team of 41 observers stationed across the USA. Observation data put the orbital distance at the time of 664.6 km (with an unstated uncertainty), and give a size for the slightly larger component, which retains the name Patroclus with overall volume equivalent to a113±3 km–diameter sphere, with the smaller component now named Menoetius with a volume equivalent to a104±3 km–diameter sphere.
Since 1989, several rotationallightcurves of Patroclus have been obtained from photometric observations. Analysis of the best rated lightcurves gave arotation period between 102.8 and 103.5 hours with a brightness amplitude of less than 0.1magnitude (U=2/3/).[15][16][17][18] A low brightness variation typically indicates that a body has a nearly spheroidal shape. Its long rotation period makes it aslow rotator.
According to the surveys carried out by the Infrared Astronomical SatelliteIRAS and NASA'sWide-field Infrared Survey Explorer with its subsequentNEOWISE mission, the Patroclus system has an effective combined size between 140.36 and 140.92 kilometers in diameter and its surface has analbedo of 0.047.[11][13] TheCollaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0471 and a diameter of 140.92 kilometers based on anabsolute magnitude of 8.19.[5]
Recent evidence suggests that the objects are icy likecomets, rather than rocky like mostasteroids. In theTholen classification, Patroclus is a darkP-type asteroid.[5]
Because the density of the components (0.88 g/cm3) is less than water and about one third that of rock, it was suggested that the Patroclus system, previously thought to be a pair of rockyasteroids, is more similar to acomet in composition.[24] It is suspected that many Jupiter trojans are in fact smallplanetesimals captured in the Lagrange point of the Jupiter–Sun system during themigration of thegiant planets 3.9 billion years ago. This scenario was proposed by A. Morbidelli and colleagues in a series of articles published in May 2005 inNature.[27]
The Patroclus–Menoetius system is a scheduled target forLucy, a flyby mission to multiple asteroids, mostlyJupiter trojans.[28]
Thisminor planet was named after the legendary Greek heroPatroclus. Friend ofAchilles, he was killed byHector during theTrojan War. (See588 Achilles and624 Hektor.) The name was proposed by Austrian astronomerJohann Palisa. The official naming citation was mentioned inThe Names of the Minor Planets byPaul Herget in 1955 (H 65).[3]
In Greek and thus in Latin,Patroclus has all short vowels. Thus the expected English pronunciation would be with stress on the 'a', */ˈpætrəkləs/. However,Alexander Pope shifted the stress to the first 'o',/pəˈtroʊkləs/, a convention from Latin poetry,[b] for metrical convenience in his verse translation of Homer, and this irregular pronunciation has become established in English.[2]
The satellite Menoetius (/məˈniːʃəs/mə-NEE-shəs; official designation (617) Patroclus I Menoetius) was named after the legendary father of Patroclus. It was previously known by theprovisional designationS/2001 (617) 1.
Patroclus and Menoetius are the only objects in the Trojan camp to be named after Greek rather than Trojan characters. The naming conventions for the Jupiter trojans were not adopted until after Patroclus was named (similarly, the asteroidHektor is the only Trojan character to appear in theGreek camp).
| Planetary satellites of |    | |
|---|---|---|
| Dwarf planet satellites of | ||
| Minor-planet moons | ||
| Ranked by size | ||
