253 Матильда астероиді: Құрамы мен ерекшеліктері

Asteroid

Mathilde (minor planet designation: 253 Mathilde) is an asteroid in the intermediate asteroid belt, approximately 50 kilometers in diameter, that was discovered by Austrian astronomer Johann Palisa at Vienna Observatory on 12 November 1885. It has a relatively elliptical orbit that requires more than four years to circle the Sun. This tumbling 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, which means the surface has a high proportion of carbon; giving it a dark surface that reflects only 4% of the light that falls on it. Among his discoveries was the asteroid 253 Mathilde, found on November 12, 1885. The initial orbital elements of the asteroid were then computed by V. A. Lebeuf, another Austrian astronomer working at the Paris Observatory. In 1995, ground based observations determined that Mathilde is a C type asteroid. It was also found to have an unusually long period of rotation of 418 hours. This was only the third asteroid to be imaged from a nearby distance, following 951 Gaspra and 243 Ida.

Mathilde is very dark, with an albedo comparable to fresh asphalt, and is thought to share the same composition as CI1 or CM2 carbonaceous chondrite meteorites, with a surface dominated by phyllosilicate minerals. The asteroid has a number of extremely large craters, with the individual craters being named for coal 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. Uniformity in brightness and 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 same is true of several C type asteroids studied by ground based telescopes equipped with adaptive optics systems (45 Eugenia, 90 Antiope, 87 Sylvia and 121 Hermione). Up to 50% of the interior volume of 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. Because of the slow rotation rate, NEAR Shoemaker was sadly 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 Mathilde.