![]() Low-resolution image of Eris and Dysnomia as imaged by the Hubble Space Telescope, August 2006 | |
Discovery | |
---|---|
Discovered by | Brown et al. [lower-alpha 1] [1] |
Discovery date | 10 September 2005 [1] |
Designations | |
Designation | Eris I |
Pronunciation | /dɪsˈnoʊmiə/ , /daɪˈsnoʊmiə/ [lower-alpha 2] |
Named after | Δυσνομία Dysnomia |
S/2005 (2003 UB313) 1 Dy /ˈdaɪ/ (nickname) Gabrielle (nickname) | |
Adjectives | Dysnomian |
Orbital characteristics [2] : 5 | |
Epoch 31 August 2006 (JD 2453979.0) | |
37273±64 km | |
Eccentricity | 0.0062±0.0010 |
15.785899±0.000050 d | |
Average orbital speed | 0.172 km/s [lower-alpha 3] |
Inclination | ≈ 0° (to Eris's equator; assumed) 78.29°±0.65°(to Eris's orbit) 45.49°±0.15°(to celestial equator) 61.59°±0.16°(to ecliptic) [lower-alpha 4] |
126.17°±0.26° | |
180.83° [lower-alpha 5] | |
Satellite of | Eris |
Physical characteristics | |
Mean diameter | 615+60 −50 km [3] : 7 |
Mass | (8.2±5.7)×1019 kg [3] : 6 |
Mean density | 0.7±0.5 g/cm3 [3] : 7 |
synchronous [4] | |
≈ 0°to orbit (assumed) | |
Albedo | 0.05±0.01 [3] : 7 |
25.4 [lower-alpha 6] | |
5.6 [lower-alpha 6] | |
Dysnomia (formally (136199) Eris I Dysnomia) is the only known moon of the dwarf planet Eris and is the second-largest known moon of a dwarf planet, after Pluto I Charon. It was discovered in September 2005 by Mike Brown and the Laser Guide Star Adaptive Optics (LGSAO) team at the W. M. Keck Observatory. It carried the provisional designation of S/2005 (2003 UB313) 1 until it was officially named Dysnomia (from the Ancient Greek word Δυσνομία meaning anarchy/lawlessness) in September 2006, after the daughter of the Greek goddess Eris. [6]
With an estimated diameter of 615+60
−50 km, Dysnomia spans 24% to 29% of Eris's diameter. It is significantly less massive than Eris, with a density consistent with it being mainly composed of ice. [3] : 8 In stark contrast to Eris's highly-reflective icy surface, Dysnomia has a very dark surface that reflects 5% of incoming visible light, [3] resembling typical trans-Neptunian objects around Dysnomia's size. [7] These physical properties indicate Dysnomia likely formed from a large impact on Eris, in a similar manner to other binary dwarf planet systems like Pluto and Orcus, and as well as the Earth–Moon system.
In 2005, the adaptive optics team at the Keck telescopes in Hawaii carried out observations of the four brightest Kuiper belt objects (Pluto, Makemake, Haumea, and Eris), using the newly commissioned laser guide star adaptive optics system. Observations taken on 10 September 2005, revealed a moon in orbit around Eris, provisionally designated S/2005 (2003 UB313) 1. In keeping with the Xena nickname that was already in use for Eris, the moon was nicknamed "Gabrielle" by its discoverers, after Xena's sidekick. [8] [9]
Submillimeter-wavelength observations of the Eris–Dysnomia system's thermal emissions by the Atacama Large Millimeter Array (ALMA) in 2015 first showed that Dysnomia had a large diameter and a very low albedo, with the initial estimate being 700±115 km. [7] Further observations by ALMA in 2018 refined Dysnomia's diameter to 615+60
−50 km (24% to 29% of Eris's diameter) and an albedo of 0.05±0.01. [3] Of the known moons of dwarf planets, only Charon is larger, making Dysnomia the second-largest moon of a dwarf planet. [10] Dysnomia's low albedo significantly contrasts with Eris's extremely high albedo of 0.96; its surface has been described to be darker than coal, [10] which is a typical characteristic seen in trans-Neptunian objects around Dysnomia's size. [7]
Eris and Dysnomia are mutually tidally locked. Astrometric observations of the Eris–Dysnomia system by ALMA show that Dysnomia does not induce detectable barycentric wobbling in Eris's position, implying its mass must be less than 1.4×1020 kg (mass ratio 0.0050±0.0035). [3] This is below the estimated mass range of (2–5)×1020 kg (mass ratio 0.01–0.03) that would normally allow Eris to be tidally locked within the range of the Solar System, [4] suggesting that Eris must therefore be unusually dissipative. [3] ALMA's upper-limit mass estimate for Dysnomia corresponds to an upper-limit density of < 1.2 g/cm3, implying a mostly icy composition. [3] The shape of Dysnomia is not known, but its low density suggests that it should not be in hydrostatic equilibrium. [11]
The brightness difference between Dysnomia and Eris decreases with longer and redder wavelengths; Hubble Space Telescope observations show that Dysnomia is 500 times fainter than Eris (6.70-magnitude difference) in visible light, [12] [5] whereas near-infrared Keck telescope observations show that Dysnomia is ~60 times fainter (4.43-magnitude difference) than Eris. [13] This indicates Dysnomia has a very different spectrum and redder color than Eris, indicating a significantly darker surface, something that has been proven by submillimeter observations. [14] [7]
Combining Keck and Hubble observations, the orbit of Dysnomia was used to determine the mass of Eris through Kepler's third law of planetary motion. Dysnomia's average orbital distance from Eris is approximately 37,300 km (23,200 mi), with a calculated orbital period of 15.786 days, or approximately half a month. [2] This shows that the mass of Eris is 1.27 times that of Pluto. [15] [16] Extensive observations by Hubble indicate that Dysnomia has a nearly circular orbit around Eris, with a low orbital eccentricity of 0.0062±0.0010. Over the course of Dysnomia's orbit, its distance from Eris varies by 462 ± 105 km (287 ± 65 mi) due to its slightly eccentric orbit. [2]
Dynamical simulations of Dysnomia suggest that its orbit should have completely circularized through mutual tidal interactions with Eris within timescales of 5–17 million years, regardless of the moon's density. A non-zero eccentricity would thus mean that Dysnomia's orbit is being perturbed, possibly due to the presence of an additional inner satellite of Eris. However, it is possible that the measured eccentricity is not real, but due to interference of the measurements by albedo features, or systematic errors. [2]
From Hubble observations from 2005 to 2018, the inclination of Dysnomia's orbit with respect to Eris's heliocentric orbit is calculated to be approximately 78°. Since the inclination is less than 90°, Dysnomia's orbit is therefore prograde relative to Eris's orbit. In 2239, Eris and Dysnomia will enter a period of mutual events in which Dysnomia's orbital plane is aligned edge-on to the Sun, allowing for Eris and Dysnomia to take turns eclipsing each other. [2]
Eight of the ten largest trans-Neptunian objects are known to have at least one satellite. Among the fainter members of the trans-Neptunian population, only about 10% are known to have satellites. [3] This is thought to imply that collisions between large KBOs have been frequent in the past. Impacts between bodies of the order of 1000 km across would throw off large amounts of material that would coalesce into a moon. A similar mechanism is thought to have led to the formation of the Moon when Earth was struck by a giant impactor (see Giant impact hypothesis) early in the history of the Solar System. [3]
Mike Brown, the moon's discoverer, chose the name Dysnomia for the moon. As the daughter of Eris, the mythological Dysnomia fit the established pattern of naming moons after gods associated with the primary body (hence, Jupiter's largest moons are named after lovers of Jupiter, while Saturn's are named after his fellow Titans). The English translation of Dysnomia, "lawlessness", also echoes Lucy Lawless, the actress who played Xena in Xena: Warrior Princess on television. Before receiving their official names, Eris and Dysnomia had been nicknamed "Xena" and "Gabrielle", though Brown states that the connection was accidental. [17]
A primary reason for the name was its similarity to the name of Brown's wife, Diane, following a pattern established with Pluto. Pluto owes its name in part to its first two letters, which form the initials of Percival Lowell, the founder of the observatory where its discoverer, Clyde Tombaugh, was working, and the person who inspired the search for "Planet X". James Christy, who discovered Charon, did something similar by adding the Greek ending -on to Char, the nickname of his wife Charlene. (Christy wasn't aware that the resulting 'Charon' was a figure in Greek mythology.) "Dysnomia", similarly, has the same first letter as Brown's wife, Diane. [18]
In astronomy, a double planet is a binary satellite system where both objects are planets, or planetary-mass objects, that share an orbital axis external to both planetary bodies.
Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest known trans-Neptunian object by volume, by a small margin, but is less massive than Eris. Like other Kuiper belt objects, Pluto is made primarily of ice and rock and is much smaller than the inner planets. Pluto has only one sixth the mass of Earth's moon, and one third its volume.
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body. Natural satellites are colloquially referred to as moons, a derivation from the Moon of Earth.
A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. As of January 2022, there are 457 minor planets known or suspected to have moons. Discoveries of minor-planet moons are important because the determination of their orbits provides estimates on the mass and density of the primary, allowing insights into their physical properties that are generally not otherwise accessible.
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Orcus is a large trans-Neptunian object located in the Kuiper belt, with one large moon, Vanth. It has an estimated diameter of 870 to 960 km, comparable to the Inner Solar System dwarf planet Ceres. Orcus had been accepted by many astronomers as a dwarf planet, though as of 2024 that consensus has changed. 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.
Chadwick A. Trujillo is an American astronomer, discoverer of minor planets and the co-discoverer of Eris, the most massive dwarf planet known in the Solar System.
Haumea is a dwarf planet located beyond Neptune's orbit. It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and disputably also in 2005 by a team headed by José Luis Ortiz Moreno at the Sierra Nevada Observatory in Spain. On September 17, 2008, it was named after Haumea, the Hawaiian goddess of childbirth, under the expectation by the International Astronomical Union (IAU) that it would prove to be a dwarf planet. Nominal estimates make it the third-largest known trans-Neptunian object, after Eris and Pluto, and approximately the size of Uranus's moon Titania.
Makemake is a dwarf planet and the second-largest of what is known as the classical population of Kuiper belt objects, with a diameter approximately that of Saturn's moon Iapetus, or 60% that of Pluto. It has one known satellite. Its extremely low average temperature, about 40 K (−230 °C), means its surface is covered with methane, ethane, and possibly nitrogen ices. Makemake shows signs of geothermal activity and thus may be capable of supporting active geology and harboring an active subsurface ocean.
38628 Huya ( hoo-YAH; provisional designation 2000 EB173) is a binary trans-Neptunian object located in the Kuiper belt, a region of icy objects orbiting beyond Neptune in the outer Solar System. Huya is classified as a plutino, a dynamical class of trans-Neptunian objects with orbits in a 3:2 orbital resonance with Neptune. It was discovered by the Quasar Equatorial Survey Team and was identified by Venezuelan astronomer Ignacio Ferrín in March 2000. It is named after Juyá, the mythological rain god of the Wayuu people native to South America.
Hiʻiaka is the larger, outer moon of the trans-Neptunian dwarf planet Haumea. It is named after one of the daughters of Haumea, Hiʻiaka, the patron goddess of the Big Island of Hawaii. It orbits once every 49.12±0.03 d at a distance of 49880±198 km, with an eccentricity of 0.0513±0.0078 and an inclination of 126.356±0.064°. Assuming its estimated diameter of over 300 km is accurate, it may be the fourth- or fifth-largest known moon of a Trans-Neptunian object, after Pluto I Charon, Eris I Dysnomia, Orcus I Vanth, and possibly Varda I Ilmarë and Salacia I Actaea.
A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough to be gravitationally rounded, but insufficient to achieve orbital dominance like the eight classical planets of the Solar System. The prototypical dwarf planet is Pluto, which was regarded as a planet before the "dwarf" concept was adopted in 2006.
Eris is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-Neptunian object (TNO) in the scattered disk and has a high-eccentricity orbit. Eris was discovered in January 2005 by a Palomar Observatory–based team led by Mike Brown and verified later that year. In September 2006, it was named after the Greco–Roman goddess of strife and discord. Eris is the ninth-most massive known object orbiting the Sun and the sixteenth-most massive overall in the Solar System. It is also the largest known object in the solar system that has not been visited by a spacecraft. Eris has been measured at 2,326 ± 12 kilometers (1,445 ± 7 mi) in diameter; its mass is 0.28% that of the Earth and 27% greater than that of Pluto, although Pluto is slightly larger by volume. Both Eris and Pluto have a surface area that is comparable to the area of Russia or South America.
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Vanth is a natural satellite or moon of the large trans-Neptunian object 90482 Orcus. It was discovered by Michael Brown and Terry-Ann Suer using images taken by the Hubble Space Telescope on 13 November 2005. The moon has a diameter of 443 km (275 mi), making it about half the size of Orcus and the third-largest moon of a trans-Neptunian object. Vanth is massive enough that it shifts the barycenter of the Orcus–Vanth system outside of Orcus, forming a binary system in which the two bodies revolve around the barycenter, much like the Pluto–Charon system. It is hypothesized that both systems formed similarly, most likely by a giant impact early in the Solar System's history. In contrast to Orcus, Vanth has a darker and slightly redder surface that apparently lacks exposed water ice, resembling primordial Kuiper belt objects.
A planetary-mass moon is a planetary-mass object that is also a natural satellite. They are large and ellipsoidal in shape. Moons may be in hydrostatic equilibrium due to tidal or radiogenic heating, in some cases forming a subsurface ocean. Two moons in the Solar System are larger than the planet Mercury : Ganymede and Titan, and seven are larger and more massive than the dwarf planets Pluto and Eris.