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Metis (
minor planet designation A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur, trans-Neptunian object and dwarf planet but not comet). Such designation always features a leading number (catalog ...
: 9 Metis) is one of the larger
main-belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
s. It is composed of silicates and
metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typica ...
lic
nickel Nickel is a chemical element with 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 slow to ...
-
iron Iron () is a chemical element with symbol Fe (from la, ferrum) 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, right in fr ...
, and may be the core remnant of a large asteroid that was destroyed by an ancient collision. Metis is estimated to contain just under half a percent of the total mass of the asteroid belt. Metis passed within 0.034AU, or , of Vesta on 19 August 2004.


Discovery and naming

Metis was discovered by Andrew Graham on 25 April 1848, at
Markree Observatory Markree Observatory was an astronomical observatory in County Sligo, Ireland. The asteroid 9 Metis was discovered from this observatory in 1848 by Cooper's assistant Andrew Graham using a comet seeker telescope. (Signed 29 April 1848; the discov ...
in Ireland; it was his only asteroid discovery. It also has been the only asteroid to have been discovered as a result of observations from Ireland until 7 October 2008, when, 160 years later, Dave McDonald from observatory J65 discovered (281507) 2008 TM9. Its name comes from the mythological
Metis Metis or Métis may refer to: Ethnic groups * Métis, recognized Indigenous communities in Canada and America whose distinct culture and language emerged after early intermarriage between First Nations peoples and early European settlers, primar ...
, a
Titaness In Greek mythology, the Titans ( grc, οἱ Τῑτᾶνες, ''hoi Tītânes'', , ''ho Tītân'') were the pre-Olympian gods. According to the ''Theogony'' of Hesiod, they were the twelve children of the primordial parents Uranus (mythology), ...
and
Oceanid In Greek mythology, the Oceanids or Oceanides (; grc, Ὠκεανίδες, Ōkeanídes, pl. of grc, Ὠκεανίς, Ōkeanís, label=none) are the nymphs who were the three thousand (a number interpreted as meaning "innumerable") daughters o ...
, daughter of Tethys and
Oceanus In Greek mythology, Oceanus (; grc-gre, , Ancient Greek pronunciation: , also Ὠγενός , Ὤγενος , or Ὠγήν ) was a Titan son of Uranus and Gaia, the husband of his sister the Titan Tethys, and the father of the river gods a ...
. The name ''Thetis'' was also considered and rejected (it would later devolve to
17 Thetis Thetis, minor planet designation 17 Thetis, is a stony asteroid from the inner regions of the asteroid belt, approximately 90 kilometers in diameter. It was discovered on 17 April 1852, by German astronomer Robert Luther at Bilk Observatory in ...
).


Characteristics

Lightcurve-based 3D-model of Metis Metis' direction of rotation is unknown at present, due to ambiguous data. Lightcurve analysis indicates that the Metidian pole points towards either
ecliptic coordinates 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 Solar System bod ...
(β, λ) = (23°, 181°) or (9°, 359°) with a 10° uncertainty.J. Torppa et al.
''Shapes and rotational properties of thirty asteroids from photometric data''
Icarus Vol. 164, p. 346 (2003).
The equivalent
equatorial coordinates The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth, a f ...
are (α, δ) = (12.7 h, 21°) or (23.7 h, 8°). 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 orbit ...
of 72° or 76°, respectively.
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
imagesA. D. Storrs et al., ''A closer look at main-belt asteroids 1: WF/PC images'', Icarus Vol. 173, p. 409 (2005).Hubble Space Telescope observations
and lightcurve analyses are in agreement that Metis has an irregular elongated shape with one pointed and one broad end. Radar observations suggest the presence of a significant flat area,D. L. Mitchell et al., ''Radar Observations of Asteroids 7 Iris, 9 Metis, 12 Victoria, 216 Kleopatra, and 654 Zelinda'', Icarus Vol. 118, p. 105 (1995). in agreement with the shape model from lightcurves. The Metidian surface composition has been estimated as 30–40% metal-bearing
olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
and 60–70% Ni- Fe metal.
Light curve In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular freq ...
data on Metis led to an assumption that it could have a
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotop ...
. However, subsequent observations failed to confirm this. Later searches with the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
in 1993 found no satellites.


Family relationships

Metis was once considered to be a member of an
asteroid family An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An a ...
known as the Metis family,J. G. Williams, ''Asteroid Families – An Initial Search'', Icarus Vol. 96, p. 251 (1992). but more recent searches for prominent families did not recognize any such group, nor is a clump evident in the vicinity of Metis by visual inspection of proper orbital element diagrams. However, a spectroscopic analysis found strong spectral similarities between Metis and
113 Amalthea 113 Amalthea () is a stony Florian asteroid and binary system from the inner regions of the asteroid belt, approximately in diameter. It was discovered on 12 March 1871, by German astronomer Robert Luther at the Bilk Observatory in Düsseldorf ...
, and it is suggested that these asteroids may be remnants of a very old (at least ~1 Ga) dynamical family whose smaller members have been pulverised by collisions or perturbed away from the vicinity. The putative parent body is estimated to have been 300 to 600 km in diameter ( Vesta-sized) and differentiated. Metis would be the relatively intact core remnant (though smaller than
16 Psyche 16 Psyche () is a large M-type asteroid discovered by the Italian astronomer Annibale de Gasparis on 17 March 1852 and named after the Greek goddess Psyche. The prefix "16" signifies that it was the sixteenth minor planet in order of di ...
), and Amalthea a fragment of the mantle, with 90% of the original body unaccounted for. Coincidentally, both Metis and Amalthea have namesakes among Jupiter's inner moons.


Occultations

In 1984 an occultation of a star produced seven
chords Chord may refer to: * Chord (music), an aggregate of musical pitches sounded simultaneously ** Guitar chord a chord played on a guitar, which has a particular tuning * Chord (geometry), a line segment joining two points on a curve * Chord (a ...
that Kristensen used to derive an ellipsoidal profile of 210×170 km. On 6 August 1989, Metis occulted a
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 ...
8.7 star producing five chords suggesting a diameter of 173.5 km. Observations of an occultation on 11 February 2006, produced only two chords indicating a minimum diameter 156 km.(Chords)
All three of these occultations fit the ellipsoid 222×182×130 km suggested by Baer. On 7 March 2014, Metis occulted the star HIP 78193 (
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 ...
7.9) over parts of Europe and the Middle East.Map


See also

* Former classification of planets *
Comet seeker A comet seeker is a type of small telescope adapted especially to searching for comets: commonly of short focal length and large aperture, in order to secure the greatest brilliancy of light. This style of telescope was used to discover the aste ...


Notes


References


External links


shape model deduced from lightcurve




* ttp://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=9 JPL Ephemeris* (displays Elong from Sun and V mag for 2011)
Globe of 9 Metis
* * {{DEFAULTSORT:000009 Flora asteroids
Metis Metis or Métis may refer to: Ethnic groups * Métis, recognized Indigenous communities in Canada and America whose distinct culture and language emerged after early intermarriage between First Nations peoples and early European settlers, primar ...
Metis Metis or Métis may refer to: Ethnic groups * Métis, recognized Indigenous communities in Canada and America whose distinct culture and language emerged after early intermarriage between First Nations peoples and early European settlers, primar ...
S-type asteroids (Tholen) 18480425