253 Mathilde
253 Mathilde is a main-belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...

Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

 about 50 km in diameter that was discovered by Johann Palisa
Johann Palisa
Johann Palisa was an Austrian astronomer, born in Opava in Austrian Silesia .He was a prolific discoverer of asteroids, discovering 122 in all, from 136 Austria in 1874 to 1073 Gellivara in 1923...

 in 1885. It has a relatively elliptical
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...

In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

 that requires more than four years to circle the Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. This asteroid has an unusually slow rate of rotation, requiring 17.4 days to complete a 360° revolution about its axis. It is a primitive C-type asteroid
C-type asteroid
C-type asteroids are carbonaceous asteroids. They are the most common variety, forming around 75% of known asteroids, and an even higher percentage in the outer part of the asteroid belt beyond 2.7 AU, which is dominated by this asteroid type...

, which means the surface has a high proportion of carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

; giving it a dark surface that reflects only 4% of the light that falls on it.

This asteroid was visited by the NEAR Shoemaker
NEAR Shoemaker
The Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a...

 spacecraft during June 1997, on its way to asteroid 433 Eros
433 Eros
433 Eros is a near-Earth asteroid discovered in 1898, and the first asteroid to be orbited by a probe . It is an S-type asteroid approximately 34.4×11.2×11.2 km in size, the second-largest NEA after 1036 Ganymed, and belongs to the Amor group.Eros is a Mars-crosser asteroid, the first known...

. During the flyby, the spacecraft imaged a hemisphere of the asteroid, revealing many large craters that have gouged out depressions in the surface. Until 21 Lutetia
21 Lutetia
21 Lutetia is a large main-belt asteroid of an unusual spectral type. It measures about 100 kilometers in diameter . It was discovered in 1852 by Hermann Goldschmidt, and is named after Lutetia, the Latin name for Paris....

 was visited in 2010, it was the largest asteroid to be visited by a spacecraft and the first C-type asteroid to be explored.

Observation history

In 1880, Johann Palisa, the director of the Austrian Naval Observatory, was offered a position as an assistant at the newly completed Vienna Observatory
Vienna Observatory
Universitäts-Sternwarte Wien is an astronomical observatory in Vienna, Austria. It is part of the University of Vienna. The first observatory was built in 1753–1754 on the roof of one of the university buildings....

. Although the job represented a demotion for Johann, it gave him access to the new 27 inches (685.8 mm) refractor, the largest telescope in the world at that time. By this point Johann had already discovered 27 asteroids, and he would employ the Vienna 27 inches (685.8 mm) and 12 inches (304.8 mm) instruments to find an additional 94 asteroids before he retired.

Among his discoveries was the asteroid 253 Mathilde, found on November 12, 1885. The initial orbital elements
Orbital elements
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are generally considered in classical two-body systems, where a Kepler orbit is used...

 of the asteroid were then computed by V. A. Lebeuf, another Austrian astronomer working at the observatory. The name of the asteroid was suggested by Lebeuf, after Mathilde, the wife of Moritz Leowy—who was the vice director of the Paris Observatory
Paris Observatory
The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world...


In 1995, ground-based observations determined that 253 Mathilde is a C-type asteroid. It was also found to have an unusually long period of rotation.

On June 27, 1997, the NEAR Shoemaker
NEAR Shoemaker
The Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a...

 spacecraft passed within 1,212 km of 253 Mathilde while moving at a velocity of 9.93 km/s. This close approach allowed the spacecraft to capture over 500 images of the surface, and provided data for more accurate determinations of the asteroid's dimensions and mass (based on gravitational perturbation of the spacecraft). However, only one hemisphere of 253 Mathilde was imaged during the fly-by. This was only the third asteroid to be imaged from a nearby distance, following 951 Gaspra
951 Gaspra
951 Gaspra is an S-type asteroid that orbits very close to the inner edge of the asteroid belt. Gaspra was the first asteroid ever to be closely approached when it was visited by the Galileo spacecraft, which flew by on its way to Jupiter on 29 October 1991.-Characteristics:Apart from a multitude...

 and 243 Ida
243 Ida
243 Ida is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Johann Palisa and named after a nymph from Greek mythology. Later telescopic observations categorized Ida as an S-type asteroid, the most numerous type in the inner asteroid belt. On 28...



253 Mathilde is very dark, with an albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 comparable to fresh asphalt
Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...

, and is thought to share the same composition as CI1 or CM2 carbonaceous chondrite
Carbonaceous chondrite
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...

A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

s, with a surface dominated by phyllosilicate minerals
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...

. The asteroid has a number of extremely large crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

s, with the individual craters being named for coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 fields and basins around the world. The two largest craters, Ishikari (29.3 km) and Karoo (33.4 km), are as wide as the asteroid's average radius. The impacts appear to have spalled large volumes off the asteroid, as suggested by the angular edges of the craters. No differences in brightness or colour were visible in the craters and there was no appearance of layering, so the asteroid's interior must be very homogeneous. There are indications of material movement along the downslope direction.

The density measured by NEAR Shoemaker, 1,300 kg/m³, is less than half that of a typical carbonaceous chondrite; this may indicate that the asteroid is very loosely packed rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...

. The same is true of several C-type asteroids studied by ground-based telescopes equipped with adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...

 systems (45 Eugenia
45 Eugenia
45 Eugenia is a large main-belt asteroid. It is famed as one of the first asteroids to be found to have a moon orbiting it. It is also the second known triple asteroid, after 87 Sylvia.- Discovery :...

, 90 Antiope
90 Antiope
The most remarkable feature of Antiope is that it consists of two components of almost equal size , making it a truly "double" asteroid. Its binary nature was discovered on 10 August 2000 by a group of astronomers using adaptive optics at the Keck Telescope on Mauna Kea. The "secondary" is...

, 87 Sylvia
87 Sylvia
87 Sylvia is one of the largest main-belt asteroids. It is a member of the Cybele group located beyond the core of the belt . Sylvia is remarkable for being the first asteroid known to possess more than one moon....

 and 121 Hermione
121 Hermione
121 Hermione is a very large asteroid of the dark C spectral type, orbiting in the Cybele group in the far outer asteroid belt. As a C-type, it is probably composed of carbonaceous materials. It was discovered in 1872, and it also has small asteroid moon discovered in 2002.-Discovery:Hermione was...

). Up to 50% of the interior volume of 253 Mathilde consists of open space. However, the existence of a 20-km-long scarp may indicate that the asteroid does have some structural strength, so it could contain some large internal components. The low interior density is an inefficient transmitter of impact shock through the asteroid, which also helps to preserve the surface features to a high degree.

Mathilde's orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

 is eccentric, taking it to the outer reaches of the main belt. Nonetheless, the orbit lies entirely between the orbits of Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 and Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

; it does not cross the planetary orbits. It also has one of the slowest rotation periods of the known asteroids—most asteroids have a rotation period in the range of 2–24 hours. Because of the slow rotation rate, NEAR Shoemaker was only able to photograph 60% of the asteroid's surface. The slow rate of rotation may be accounted for by a satellite orbiting the asteroid, but a search of the NEAR images revealed none larger than 10 km in diameter out to 20 times the radius of 253 Mathilde.

External links

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