_mathilde_crop.jpg) 253 Mathilde as seen byNEAR in 1997 | |
| Discovery[1] | |
|---|---|
| Discovered by | J. Palisa |
| Discovery site | Vienna Obs. |
| Discovery date | 12 November 1885 |
| Designations | |
| (253) Mathilde | |
| Pronunciation | /məˈtɪldə/ |
Named after | Mathilde Loewy |
| A885 VA, 1915 TN 1949 OL1 | |
| Main belt | |
| Orbital characteristics[2] | |
| Epoch 31 July 2016 (JD 2457600.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 130.38 yr (47622 d) |
| Aphelion | 3.35003411 AU (501.157970 Gm) |
| Perihelion | 1.9467702 AU (291.23268 Gm) |
| 2.648402147 AU (396.1953219 Gm) | |
| Eccentricity | 0.26492652 |
| 4.31yr (1574.3d) | |
Averageorbital speed | 17.98 km/s[3] |
| 170.584348° | |
| 0° 13m 43.248s / day | |
| Inclination | 6.7427122° |
| 179.58936° | |
| 157.39642° | |
| Earth MOID | 0.939032 AU (140.4772 Gm) |
| Jupiter MOID | 2.06073 AU (308.281 Gm) |
| TJupiter | 3.331 |
| Physical characteristics | |
| Dimensions | 52.8 km[2] (66×48×46 km[4]) |
| Mass | (1.033±0.044)×1017 kg[5] |
Meandensity | 1.3 g/cm3[5] |
Equatorialsurface gravity | 0.00989 m/s2 |
Equatorialescape velocity | 22.9 m/s |
| 417.7 h (17.40 d)[2] 17.406 ± 0.010 d[6] (17 d 9 h 45 min) | |
| 0.0436±0.004[2] | |
| Temperature | ≈ 174[7]K |
| Cb[2] | |
| 10.3[2] | |
253 Mathilde is anasteroid in the intermediateasteroid belt, approximately 50 kilometers in diameter, that was discovered by Austrian astronomerJohann Palisa atVienna Observatory on 12 November 1885. It has a relativelyellipticalorbit that requires more than four years to circle the Sun. Thistumbling asteroid has an unusuallyslow rate of rotation, requiring 17.4 days to complete a 360°revolution about its axis. It is a primitiveC-type asteroid, which means the surface has a high proportion ofcarbon; giving it a dark surface that reflects only 4% of the light that falls on it.[8]
Mathilde was visited by theNEAR Shoemaker spacecraft during June 1997, on its way to asteroid433 Eros. During the short flyby, the spacecraft imaged a hemisphere of the asteroid, revealing many large craters that had gouged out depressions in the surface. It was the first carbonaceous asteroid to be explored and, until21 Lutetia was visited in 2010, it was the largest asteroid to bevisited by a spacecraft.
In 1880, Johann Palisa, the director of the Austrian Naval Observatory (538), was offered a position as an assistant at the newly completedVienna Observatory. Although the job represented a demotion for Johann, it gave him access to the new 27-inch (690 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-inch (690 mm) and 12-inch (300 mm) instruments to find an additional 94 asteroids before he retired.[9]
Among his discoveries was the asteroid 253 Mathilde, found on 12 November 1885. The initialorbital elements of the asteroid were then computed by V. A. Lebeuf, another Austrian astronomer working at theParis Observatory.[10] The name of the asteroid was suggested by Lebeuf, after Mathilde, the wife ofMoritz Loewy—who was the vice director of the observatory in Paris.[1][10]
In 1995, ground-based observations determined that Mathilde is aC-type asteroid. It was also found to have an unusually long period of rotation of 418 hours.[10]
On 27 June 1997, theNEAR Shoemaker spacecraft passed within 1,212 km of 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,[8] and provided data for more accurate determinations of the asteroid's dimensions and mass (based on gravitational perturbation of the spacecraft).[5] However, only one hemisphere of Mathilde was imaged during the fly-by.[11] This was only the third asteroid to be imaged from a nearby distance, following951 Gaspra and243 Ida.
Mathilde is very dark, with analbedo comparable to freshasphalt,[12] and is thought to share the same composition as CI1 or CM2carbonaceous chondritemeteorites, with a surface dominated byphyllosilicate minerals.[13] The asteroid has a number of extremely largecraters, with the individual craters being named forcoal fields and basins around the world.[14] The two largest craters, Ishikari (29.3 km) and Karoo (33.4 km), are as wide as the asteroid's average radius.[4] The impacts appear to have spalled large volumes off the asteroid, as suggested by the angular edges of the craters.[8] 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.[4]
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 packedrubble pile.[5] The same is true of several C-type asteroids studied by ground-based telescopes equipped withadaptive optics systems (45 Eugenia,90 Antiope,87 Sylvia and121 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.[11] 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.[4]
Mathilde'sorbit iseccentric, taking it to the outer reaches of the belt. Nonetheless, the orbit lies entirely between the orbits ofMars andJupiter; 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.[15] 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 Mathilde.[16]
