Discovery | |
---|---|
Discovered by | Annibale de Gasparis |
Discovery date | 5 April 1853 |
Designations | |
(24) Themis | |
Pronunciation | /ˈθiːmɪs/ [1] |
Named after | Themis |
1947 BA; 1955 OH | |
Main belt (Themis) | |
Adjectives | Themistian [2] /θɪˈmɪstiən/ [3] |
Orbital characteristics [4] | |
Epoch 23 July 2010 (JD 2455400.5) | |
Aphelion | 529.4 Gm (3.539 AU) |
Perihelion | 406.8 Gm (2.719 AU) |
468.1 Gm (3.129 AU) | |
Eccentricity | 0.1310 |
2021 d (5.54 yr) | |
146.6° | |
Inclination | 0.7595° |
35.99° | |
107.7° | |
Physical characteristics | |
Dimensions | c/a = 0.76±0.08 [5] |
Mean diameter | 208±3 km [5] 198±20 km [6] |
Mass | (6.2±2.9)×1018 kg [5] (11.3±4.3)×1018 kg [6] 2.3×1019 kg [7] [8] |
Mean density | 1.31±0.62 g/cm3 [5] 2.78±1.35 g/cm3 [6] |
Equatorial surface gravity | 0.15+0.08 −0.07 m/s2 [6] |
Equatorial escape velocity | 87+15 −20 m/s [6] |
0.34892 d(8 h 23 min) [4] | |
0.060 (calculated) [5] 0.067 [4] | |
C/B [4] (B-V=0.68) | |
7.08 [4] | |
Themis (minor planet designation: 24 Themis) is one of the largest asteroids in the asteroid belt. It is also the largest member of the Themistian family. It was discovered by Annibale de Gasparis on 5 April 1853. It is named after Themis, the personification of natural law and divine order in Greek mythology.
Not to be confused with 269 Justitia, named for Justitia, Themis' Roman name.
24 Themis was discovered on 5 April 1853 by Annibale de Gasparis of Naples, though it was given its name by fellow Italian astronomer Angelo Secchi. The asteroid was named after Themis, the Greek goddess of law. [9] Gravitational perturbations in the orbit of Themis were used to calculate the mass of Jupiter as early as 1875. [10]
On 24 December 1975, 24 Themis had a close encounter with 2296 Kugultinov with a minimum distance of 0.016 AU (2.4×10 6 km). By analyzing the perturbation of Kugultinov's orbit due to the gravitational pull of Themis, the mass of Themis was determined to be approximately 2.89×10−11 solar masses [11] (9.62×10−6 Earth masses).
Themis is in an elliptical orbit around the Sun with an eccentricity of 0.1306 and an inclination of 0.76°. [12] It has an orbital period of 5.54 years. The distance between Themis and the Sun ranges from 2.71 AU at perihelion and 3.55 AU at aphelion, [13] with a mean distance of 3.1302 AU. [12] Themis is part of the Themis family of asteroids, which is located in the outer part of the main belt. The family consists of a core of large objects surrounded by a cloud of smaller objects; 24 Themis is a member of the core. [13]
On 7 October 2009, the presence of water ice was confirmed on the surface of this asteroid using NASA’s Infrared Telescope Facility. [14] [15] The surface of the asteroid appears completely covered in ice. As this ice layer is sublimated, it may be getting replenished by a reservoir of ice under the surface. [16] [17]
Scientists hypothesize that some of the first water brought to Earth was delivered by asteroid impacts after the collision that produced the Moon. The presence of ice on 24 Themis supports this theory. [16] Because of its proximity to the sun (~3.2 AU), the widespread ice on the surface of 24 Themis is somewhat unexpected. The surface ice may be replenished by a sub-surface reservoir of water or impact gardening—a lunar phenomenon in which the moon overturns surface material at a rate of 1 m/ Gyr. [16]
An alternative mechanism to explain the presence of water ice on 24 Themis is similar to the hypothesized formation of water on the surface of the Moon by solar wind. Trace amounts of water would be continuously produced by high-energy solar protons impinging oxide minerals present at the surface of the asteroid. The hydroxyl surface groups (S–OH) formed by the collision of protons (H+
) with oxygen atoms present at oxide surface (S=O) can further be converted in water molecules (H
2O) adsorbed onto the oxide minerals surface. The chemical rearrangement supposed at the oxide surface could be schematically written as follows:
or,
where S represents the oxide surface. [15]
Organic compounds were also detected on the surface of Themis [16] [17] in the form of tholins, high-molecular weight organics found in the outer solar system, distinguished by a brown or reddish color in optical spectra. Compounds found in the spectra of Themis include ice tholin (the residual of an irradiated mixture of water ice and ethane), asphaltite, carbonaceous meteorite material, and polycyclic aromatic hydrocarbons. [17] [18]
Water presence on other celestial bodies:
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has an orbital semi-major axis of 30.1 astronomical units (au).
In planetary astronomy, a centaur is a small Solar System body that orbits the Sun between Jupiter and Neptune and crosses the orbits of one or more of the giant planets. Centaurs generally have unstable orbits because they cross or have crossed the orbits of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years, but there is one known centaur, 514107 Kaʻepaokaʻawela, which may be in a stable orbit. Centaurs typically exhibit the characteristics of both asteroids and comets. They are named after the mythological centaurs that were a mixture of horse and human. Observational bias toward large objects makes determination of the total centaur population difficult. Estimates for the number of centaurs in the Solar System more than 1 km in diameter range from as low as 44,000 to more than 10,000,000.
28978 Ixion (, provisional designation 2001 KX76) is a large trans-Neptunian object and a possible dwarf planet. It is located in the Kuiper belt, a region of icy objects orbiting beyond Neptune in the outer Solar System. Ixion is classified as a plutino, a dynamical class of objects in a 2:3 orbital resonance with Neptune. It was discovered in May 2001 by astronomers of the Deep Ecliptic Survey at the Cerro Tololo Inter-American Observatory, and was announced in July 2001. The object is named after the Greek mythological figure Ixion, who was a king of the Lapiths.
Tholins are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon dioxide, methane or ethane, often in combination with nitrogen or water. Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups, typically nitriles and hydrocarbons, and their degraded forms such as amines and phenyls. Tholins do not form naturally on modern-day Earth, but they are found in great abundance on the surfaces of icy bodies in the outer Solar System, and as reddish aerosols in the atmospheres of outer Solar System planets and moons.
Orcus is a large trans-Neptunian object with a large moon, Vanth. It has a diameter of 870 to 960 km, the size of or somewhat smaller than the Inner Solar System dwarf planet Ceres. Orcus is generally accepted by astronomers as a dwarf planet, although there is some doubt. The surface of Orcus is relatively bright with albedo reaching 23 percent, neutral in color and rich in water ice. The ice is predominantly in crystalline form, which may be related to past cryovolcanic activity. Other compounds like methane or ammonia may also be present on its surface. Orcus was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.
Sedna is a dwarf planet in the outermost reaches of the Solar System discovered in 2003. Spectroscopy has revealed that Sedna's surface composition is largely a mixture of water, methane, and nitrogen ices with tholins, similar to those of some other trans-Neptunian objects. Its surface is one of the reddest among Solar System objects. Sedna, within estimated uncertainties, is tied with Ceres as the largest planetoid not known to have a moon. It has a diameter of approximately 1,000 km ; its mass is unknown.
Hygiea is a major asteroid and possible dwarf planet located in the main asteroid belt. With a mean diameter of 425 to 440 km and a mass estimated to be 3% of the total mass of the belt, it is the fourth-largest asteroid in the Solar System by both volume and mass, and is either the second largest of the C-type asteroids after 1 Ceres, or the largest in classifications that use G type for Ceres.
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. It is the largest Eunomian asteroid, and is estimated to contain 1% of the mass of the asteroid belt.
Fortuna is one of the largest main-belt asteroids. It has a composition similar to 1 Ceres: a darkly colored surface that is heavily space-weathered with the composition of primitive organic compounds, including tholins.
Massalia, minor planet designation 20 Massalia, is a stony asteroid and the parent body of the Massalia family located in the inner region of the asteroid belt, approximately 145 kilometers in diameter. Discovered by Italian astronomer Annibale de Gasparis on 19 September 1852, it was named for the French city of Marseille, from which the independent discover Jean Chacornac sighted it the following night.
Klymene is a large, dark Themistian asteroid that was discovered by J. C. Watson on September 13, 1868, and named after one of the many Clymenes in Greek mythology. It is orbiting the Sun with a period of 5.60 years and an eccentricity of 0.16. The orbital plane is inclined by 2.8° to the plane of the ecliptic. It is classified as a C-type asteroid, indicating it probably has a carbonaceous composition. The spectra indicates the presence of aqueous-altered minerals on the surface based upon a sharp feature at a wavelength of 3 μm, and, as of 2015, is the only member of the Themis family found to show this absorption.
The Themis family is a family of carbonaceous asteroids located in the outer portion of the asteroid belt, at a mean distance of 3.13 AU from the Sun. It is one of the largest families with over 4700 known members, and consists of a well-defined core of larger bodies surrounded by a region of smaller ones. The collisional Themis family is named after its parent body, the asteroid 24 Themis, discovered on 5 April 1853 by Italian astronomer Annibale de Gasparis.
Justitia is a fairly sizeable main belt asteroid around 50 km in diameter
1764 Cogshall, provisional designation 1953 VM1, is a carbonaceous Themistian asteroid from the outer regions of the asteroid belt, approximately 26 kilometers in diameter. It was discovered on 7 November 1953, by astronomers of the Indiana Asteroid Program at Goethe Link Observatory in Indiana, United States. The asteroid was named after Wilbur Cogshall, professor of astronomy at Indiana University.
3054 Strugatskia, provisional designation 1977 RE7, is a dark Themistian asteroid from the outer regions of the asteroid belt, approximately 27 kilometers (17 miles) in diameter. It was discovered on 11 September 1977, by Soviet–Russian astronomer Nikolai Chernykh at the Crimean Astrophysical Observatory in Nauchnij, on the Crimean peninsula. The asteroid was named after the brothers Arkady and Boris Strugatsky, two Russian science fiction authors.
2325 Chernykh, provisional designation 1979 SP, is a dark Themistian asteroid from the outer regions of the asteroid belt, approximately 23 kilometers in diameter. It was discovered on 25 September 1979, by Czech astronomer Antonín Mrkos at the Klet Observatory in the Czech Republic. The asteroid was named after Russian astronomer couple Lyudmila Chernykh and Nikolai Chernykh.
2296 Kugultinov, provisional designation 1975 BA1, is a carbonaceous Themistian asteroid from the outer region of the asteroid belt, approximately 20 kilometers in diameter.
Gonggong is a dwarf planet, a member of the scattered disc beyond Neptune. It has a highly eccentric and inclined orbit during which it ranges from 34–101 astronomical units from the Sun. As of 2019, its distance from the Sun is 88 AU, and it is the sixth-farthest known Solar System object. According to the Deep Ecliptic Survey, Gonggong is in a 3:10 orbital resonance with Neptune, in which it completes three orbits around the Sun for every ten orbits completed by Neptune. Gonggong was discovered in July 2007 by American astronomers Megan Schwamb, Michael Brown, and David Rabinowitz at the Palomar Observatory, and the discovery was announced in January 2009.
(55638) 2002 VE95, prov. designation: 2002 VE95, is a trans-Neptunian object from the outermost region of the Solar System. It was discovered on 14 November 2002, by astronomers with the Near-Earth Asteroid Tracking program at the Palomar Observatory in California, United States. This resonant trans-Neptunian object is a member of the plutino population, locked in a 2:3 resonance with Neptune. The object is likely of primordial origin with a heterogeneous surface and a notably reddish color (RR) attributed to the presence of methanol and tholins. It has a poorly defined rotation period of 6.8 hours and measures approximately 250 kilometers (160 miles) in diameter, too small to be a dwarf planet candidate. As of 2021, it has not yet been named.
A planetary surface is where the solid or liquid material of certain types of astronomical objects contacts the atmosphere or outer space. Planetary surfaces are found on solid objects of planetary mass, including terrestrial planets, dwarf planets, natural satellites, planetesimals and many other small Solar System bodies (SSSBs). The study of planetary surfaces is a field of planetary geology known as surface geology, but also a focus on a number of fields including planetary cartography, topography, geomorphology, atmospheric sciences, and astronomy. Land is the term given to non-liquid planetary surfaces. The term landing is used to describe the collision of an object with a planetary surface and is usually at a velocity in which the object can remain intact and remain attached.