Discovery | |
---|---|
Discovered by | Annibale de Gasparis |
Discovery site | Naples Obs. |
Discovery date | 29 July 1851 |
Designations | |
(15) Eunomia | |
Pronunciation | /juːˈnoʊmiə/ [1] |
Named after | Eunomia |
Adjectives | Eunomian /juːˈnoʊmiən/ [2] |
Symbol | (historical) |
Orbital characteristics [3] | |
Epoch July 01, 2021 (JD 2459396.5, heliocentric) | |
Aphelion | 3.14 AU (469 Gm) |
Perihelion | 2.15 AU (321 Gm) |
2.644 AU (395 Gm) | |
Eccentricity | 0.186 |
4.30 yr (1571 d) | |
206° | |
Inclination | 11.75° |
293° | |
99° | |
Physical characteristics | |
Dimensions | c/a = 0.53±0.02 [4] (357×255×212)±15 km [5] |
Mean diameter | 270±3 km [4] 268 km [5] |
Mass | (30.5±1.9)×1018 kg [4] (31.8±0.3)×1018 kg [(15.97±0.15)×10−12 M☉] [5] |
Mean density | 2.96±0.21 g/cm3 [4] 3.14±0.53 g/cm3 [5] |
6.083 h (0.2535 d) [3] | |
0.187 [4] 0.25±4 geometric (0.84±0.02 BV, 0.45±0.02 UB) [3] | |
S-type asteroid [3] | |
7.9 [6] to 11.24 | |
5.41 [3] | |
0.29″ to 0.085″ | |
Eunomia (minor planet designation 15 Eunomia) is a very large asteroid in the middle asteroid belt. It is the largest of the stony (S-type) asteroids, with 3 Juno as a close second. It is quite a massive asteroid, in 6th to 8th place (to within measurement uncertainties). It is the largest Eunomian asteroid, and is estimated to contain 1% of the mass of the asteroid belt. [7] [8]
Eunomia was discovered by Annibale de Gasparis on July 29, 1851, and named after Eunomia, one of the Horae (Hours), a personification of order and law in Greek mythology. Its historical symbol is a heart with a star on top; it is in the pipeline for Unicode 17.0 as U+1CEC8 ( ). [9] [10]
As the largest S-type asteroid (with 3 Juno being a very close second), Eunomia has attracted a moderate amount of scientific attention.
Eunomia appears to be an elongated but fairly regularly shaped body, with what appear to be four sides of differing curvature and noticeably different average compositions. [11] Its elongation led to the suggestion that Eunomia may be a binary object, but this has been refuted. [12] It is a retrograde rotator with its pole pointing towards ecliptic coordinates (β, λ) = (−65°, 2°) with a 10° uncertainty. [11] [12] This gives an axial tilt of about 165°.
Like other true members of the family, its surface is composed of silicates and some nickel-iron, and is quite bright. Calcium-rich pyroxenes and olivine, along with nickel-iron metal, have been detected on Eunomia's surface. Spectroscopic studies suggest that Eunomia has regions with differing compositions: A larger region dominated by olivine, which is pyroxene-poor and metal-rich, and another somewhat smaller region on one hemisphere (the less pointed end) that is noticeably richer in pyroxene, [11] and has a generally basaltic composition. [13]
This composition indicates that the parent body was likely subject to magmatic processes, and became at least partially differentiated under the influence of internal heating in the early period of the Solar System. The range of compositions of the remaining Eunomian asteroids, formed by a collision of the common parent body, is large enough to encompass all the surface variations on Eunomia itself. The majority of smaller Eunomian asteroids are more pyroxene rich than Eunomia's surface, and contain very few metallic (M-type) bodies.
Altogether, these lines of evidence suggest that Eunomia is the central remnant of the parent body of the Eunomia family, which was stripped of most of its crustal material by the disrupting impact, but was perhaps not disrupted itself. However, there is uncertainty over Eunomia's internal structure and relationship to the parent body. Computer simulations of the collision [14] are more consistent with Eunomia being a re-accumulation of most of the fragments of a completely shattered parent body, yet Eunomia's quite high density would indicate that it is not a rubble pile after all. Whatever the case in this respect, it appears that any metallic core region, if present, has not been exposed.
An older explanation of the compositional differences, that Eunomia is a mantle fragment of a far larger parent body (with a bit of crust on one end, and a bit of core on the other), appears to be ruled out by studies of the mass distribution of the entire Eunomia family. These indicate that the largest fragment (that is, Eunomia) has about 70% of the mass of the parent body, [15] which is consistent with Eunomia being a central remnant, with the crust and part of the mantle stripped off.
These indications are also in accord with recent mass determinations which indicate that Eunomia's density is typical of mostly intact stony asteroids, and not the anomalously low "rubble pile" density of ~1 g/cm3 that had been reported earlier.
15 Eunomia was in study of asteroids using the Hubble FGS. [16] Asteroids studied include (63) Ausonia, (15) Eunomia, (43) Ariadne, (44) Nysa, and (624) Hektor. [16]
The orbit of 15 Eunomia places it in a 7:16 mean-motion resonance with the planet Mars. Eunomia is used by the Minor Planet Center to calculate perturbations. [17] The computed Lyapunov time for this asteroid is 25,000 years, indicating that it occupies a chaotic orbit that will change randomly over time because of gravitational perturbations of the planets. [18]
Eunomia has been observed occulting stars three times. It has a mean opposition magnitude of +8.5, [19] about equal to the mean brightness of Titan, and can reach +7.9 at a near perihelion opposition.
Asteroid (50278) 2000 CZ12 passed about 0.00037 AU (55,000 km ; 34,000 mi ) from Eunomia on March 4, 2002. [20]
624 Hektor is the largest Jupiter trojan and the namesake of the Hektor family, with a highly elongated shape equivalent in volume to a sphere of approximately 225 to 250 kilometers diameter. It was discovered on 10 February 1907, by astronomer August Kopff at Heidelberg Observatory in southwest Germany, and named after the Trojan prince Hector, from Greek mythology. It has one small 12-kilometer sized satellite, Skamandrios, discovered in 2006.
Ariadne is a fairly large and bright main-belt asteroid. It is the second-largest member of the Flora asteroid family. It was discovered by N. R. Pogson on 15 April 1857 and named after the Greek heroine Ariadne.
Nysa is a large and very bright main-belt asteroid, and the brightest member of the Nysian asteroid family. It is classified as a rare class E asteroid and is probably the largest of this type.
The Eunomia or Eunomian family is a large asteroid family of S-type asteroids named after the asteroid 15 Eunomia. It is the most prominent family in the intermediate asteroid belt and the 6th-largest family with nearly six thousand known members, or approximately 1.4% of all asteroids in the asteroid belt.
Ausonia is a stony Vestian asteroid from the inner region of the asteroid belt, approximately 100 kilometers in diameter. It was discovered by Italian astronomer Annibale de Gasparis on 10 February 1861, from the Astronomical Observatory of Capodimonte, in Naples, Italy. The initial choice of name for the asteroid was "Italia", after Italy, but this was modified to Ausonia, an ancient classical name for the Italian region.
Io is carbonaceous asteroid in the central region of the asteroid belt, approximately 170 kilometers in diameter. It is an identified Eunomian interloper.
Thisbe, minor planet designation 88 Thisbe, is the 13th largest main-belt asteroid. It was discovered by C. H. F. Peters on June 15, 1866, and named after Thisbe, heroine of a Roman fable. This asteroid is orbiting the Sun at a distance of 2.768 AU with a period of 4.60 years and an orbital eccentricity (ovalness) of 0.165. The orbital plane is inclined at an angle of 5.219° to the ecliptic.
115 Thyra is a fairly large and bright inner main-belt asteroid that was discovered by Canadian-American astronomer J. C. Watson on August 6, 1871 and was named for Thyra, the consort of King Gorm the Old of Denmark. Based upon its spectrum, it is categorized as a stony S-type asteroid.
704 Interamnia is a large F-type asteroid. With a mean diameter of around 330 kilometres, it is the fifth-largest asteroid, after Ceres, Vesta, Pallas and Hygiea. Its mean distance from the Sun is 3.067 AU. It was discovered on 2 October 1910 by Vincenzo Cerulli, and named after the Latin name for Teramo, Italy, where Cerulli worked. Its mass is probably between fifth and tenth highest in the asteroid belt, with a mass estimated to be 1.2% of the mass of the entire asteroid belt. Observations by the Very Large Telescope's SPHERE imager in 2017–2019, combined with occultation results, indicate that the shape of Interamnia may be consistent with hydrostatic equilibrium for a body of its density with a rotational period of 7.6 hours. This suggests that Interamnia may have formed as an equilibrium body, and that impacts changed its rotational period after it fully solidified.
881 Athene is a stony background asteroid from the central region of the asteroid belt. It was discovered on 22 July 1917, by astronomer Max Wolf at the Heidelberg-Königstuhl State Observatory in southwest Germany. The likely elongated S/L-type asteroid has a rotation period of 13.9 hours and measures approximately 12 kilometers in diameter. It was named after Athena, the goddess of wisdom in Greek mythology.
1050 Meta, provisional designation 1925 RC, is a stony Eunomia asteroid from the central regions of the asteroid belt, approximately 10 kilometers in diameter. It was discovered on 14 September 1925, by German astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany. The meaning of the asteroids's name is unknown. The presumably S-type asteroid has a rotation period of 6.14 hours and possibly an elongated shape.
(24835) 1995 SM55, provisional designation 1995 SM55, is a trans-Neptunian object and member of the Haumea family that resides in the Kuiper belt, located in the outermost region of the Solar System. It was discovered on 19 September 1995, by American astronomer Nichole Danzl of the Spacewatch program at Kitt Peak National Observatory near Tucson, Arizona, in the United States. It measures approximately 200 kilometers in diameter and was the second-brightest known object in the Kuiper belt, after Pluto, until 1996 TO66 was discovered.
88611 Teharonhiawako, or (88611) Teharonhiawako–Sawiskera as a binary, is a trans-Neptunian object and a member of the cold classical Kuiper belt, measuring about 220 km in diameter. It is a binary object, with a large companion named Sawiskera, which at 126 km in diameter is about two-thirds the size of its primary.
83982 Crantor, prov. designation: 2002 GO9, is a centaur in a 1:1 resonance with Uranus, approximately 60 kilometers (37 miles) in diameter. It was discovered on 12 April 2002, by astronomers of the Near-Earth Asteroid Tracking at the Palomar Observatory in California, United States. This minor planet was named for Crantor from Greek mythology.
31824 Elatus (, provisional designation: 1999 UG5) is a very red centaur from the outer Solar System, approximately 48 kilometers (30 miles) in diameter. It was discovered on 29 October 1999, by astronomers of the Catalina Sky Survey at Mount Lemmon Observatory in Arizona, United States. The minor planet was named after Elatus, a centaur from Greek mythology.
9175 Graun, provisional designation 1990 OO2, is a stony Eunomian asteroid from the central region of the asteroid belt, approximately 10 kilometers in diameter. It was discovered on 29 July 1990, by American astronomer Henry E. Holt at Palomar Observatory in California, United States. The asteroid was later named for American author and amateur astronomer Ken Graun.
32532 Thereus, provisional designation: 2001 PT13, is a centaur from the outer Solar System, approximately 80 kilometers (50 miles) in diameter. It was discovered on 9 August 2001, by astronomers of the Near-Earth Asteroid Tracking program at the Palomar Observatory in California, United States. This minor planet was named for the phrase thēreios bia 'beastly strength', used to describe centaurs in Greek mythology.
(469306) 1999 CD158, provisional designation: 1999 CD158, is a trans-Neptunian object from the circumstellar disc of the Kuiper belt, located in the outermost region of the Solar System. The relatively bright hot classical Kuiper belt object measures approximately 310 kilometers (190 miles) in diameter. It was discovered on 10 February 1999, by American astronomers Jane Luu, David Jewitt and Chad Trujillo at Mauna Kea Observatories on the Big Island of Hawaii, United States.
(82158) 2001 FP185, provisional designation 2001 FP185, is a highly eccentric trans-Neptunian object from the scattered disc in the outermost part of the Solar System, approximately 330 kilometers in diameter. It was discovered on 26 March 2001, by American astronomer Marc Buie at Kitt Peak National Observatory in Arizona, United States.
Fine Guidance Sensor (FGS) for the Hubble Space Telescope is a system of three instruments used for pointing the telescope in space, and also for astrometry and its related sciences. To enable aiming the telescope at a specific spot in the sky, each FGS combines optics and electronics. There are three Hubble FGS, and they have been upgraded over the lifetime of the telescope by crewed Space Shuttle missions. The instruments can support pointing of 2 milli-arc seconds. The three FGS are part of the Hubble Space Telescope's Pointing Control System, aka PCS. The FGS function in combination with the Hubble main computer and gyroscopes, with the FGS providing data to the computer as sensors which enables the HST to track astronomical targets.
Eunomia 0.164E−11 solar masses; asteroid belt 15E−11 solar masses → 1.1%.