15 Eunomia
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15 Eunomia is a very large
asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...
in the middle
asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...
. It is the largest of the stony ( S-type) asteroids, with
3 Juno Juno (minor-planet designation: 3 Juno) is a large asteroid in the asteroid belt. Juno was the third asteroid discovered, in 1804, by German astronomer Karl Harding. It is tied with three other asteroids as the thirteenth largest asteroid, and ...
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. Eunomia was discovered by
Annibale de Gasparis Annibale de Gasparis (; 9 November 1819 – 21 March 1892) was an Italian astronomer, known for discovering asteroids and his contributions to theoretical astronomy. Biography De Gasparis was born in 1819 in Bugnara to Angelo de Gasparis ...
on July 29, 1851, and named after Eunomia, one of the
Horae In Greek mythology, the Horae (), Horai () or Hours (, ) were the goddesses of the seasons and the natural portions of time. Etymology The term ''hora'' comes from the Proto-Indo-European ("year"). Function The Horae were originally the ...
(Hours), a personification of order and
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in
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. Its historical symbol is a heart with a star on top; it is in the pipeline for
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17.0 as U+1CEC8 𜻈 ().


Characteristics

As the largest S-type asteroid (with
3 Juno Juno (minor-planet designation: 3 Juno) is a large asteroid in the asteroid belt. Juno was the third asteroid discovered, in 1804, by German astronomer Karl Harding. It is tied with three other asteroids as the thirteenth largest asteroid, and ...
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. Its elongation led to the suggestion that Eunomia may be a
binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two values (0 and 1) for each digit * Binary function, a function that takes two arguments * Binary operation, a mathematical op ...
object, but this has been refuted. It is a
retrograde Retrograde may refer to: Film and television * Retrograde (2004 film), ''Retrograde'' (2004 film), a film by Christopher Kulikowski * Retrograde (2022 American film), ''Retrograde'' (2022 American film), a documentary film by Matthew Heineman * ...
rotator with its pole pointing towards
ecliptic coordinates In astronomy, the ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small So ...
(β, λ) = (−65°, 2°) with a 10° uncertainty. This gives an
axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbita ...
of about 165°. Like other true members of the family, its surface is composed of
silicate A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...
s and some
nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
-
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
, and is quite bright.
Calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
-rich
pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...
s and
olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
, along with nickel-iron metal, have been detected on Eunomia's surface.
Spectroscopic Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectrosc ...
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, and has a generally
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic composition. This composition indicates that the parent body was likely subject to
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
tic processes, and became at least partially differentiated under the influence of
internal heat Internal heat is the heat source from the interior of celestial objects, such as stars, brown dwarfs, planets, moons, dwarf planets, and (in the early history of the Solar System) even asteroids such as Vesta, resulting from contraction caused ...
ing 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 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, 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 ~ that had been reported earlier.


Studies

15 Eunomia was in study of asteroids using the Hubble FGS. Asteroids studied include (63) Ausonia, (15) Eunomia, (43) Ariadne, (44) Nysa, and (624) Hektor.


Orbit

The orbit of 15 Eunomia places it in a 7:16
mean-motion resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...
with the planet
Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...
. Eunomia is used by the
Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Funct ...
to calculate perturbations. The computed
Lyapunov time In mathematics, the Lyapunov time is the characteristic timescale on which a dynamical system is chaotic. It is named after the Russian mathematician Aleksandr Lyapunov. It is defined as the inverse of a system's largest Lyapunov exponent. Use T ...
for this asteroid is 25,000 years, indicating that it occupies a chaotic orbit that will change randomly over time because of
gravitational perturbation In astronomy, perturbation is the complex motion of a massive body subjected to forces other than the gravitational attraction of a single other massive body. The other forces can include a third (fourth, fifth, etc.) body, resistance, as fro ...
s of the planets. Eunomia has been observed
occulting An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s three times. It has a mean
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magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
of +8.5, about equal to the
mean A mean is a quantity representing the "center" of a collection of numbers and is intermediate to the extreme values of the set of numbers. There are several kinds of means (or "measures of central tendency") in mathematics, especially in statist ...
brightness of
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
, and can reach +7.9 at a near
perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...
opposition. Asteroid passed about from Eunomia on March 4, 2002.


Trivia

The asteroid's shape served as the inspiration to alien species' craft's shape in the movie
Arrival Arrival(s) or The Arrival(s) may refer to: Film * ''The Arrival'' (1991 film), an American science fiction horror film * ''The Arrival'' (1996 film), an American-Mexican science fiction horror film * ''Arrival'' (film), a 2016 American science ...


See also

* Former classification of planets


Notes


References


External links


shape model deduced from lightcurve, including composition variations across the surface
* (displays Elong from Sun and V mag for 2011) * * {{DEFAULTSORT:000015 Eunomia asteroids Eunomia Eunomia S-type asteroids (Tholen) S-type asteroids (SMASS) 18510729