951 Gaspra
NASA image of Gaspra; colors are exaggerated
|
|
| Discovery | |
|---|---|
| Discovered by | G. N. Neujmin |
| Discovery date | 30 July 1916 |
| Designations | |
|
Named after
|
Gaspra |
| SIGMA 45; A913 YA; 1955 MG1 |
|
| Main belt (Flora family) | |
| Orbital characteristics | |
| Epoch 6 March 2006 (JD 2453800.5) | |
| Aphelion | 2.594 AU (388.102 Gm) |
| Perihelion | 1.825 AU (272.985 Gm) |
| 2.210 AU (330.544 Gm) | |
| Eccentricity | 0.174 |
| 3.28 a (1199.647 d) | |
|
Average orbital speed
|
19.88 km/s |
| 53.057° | |
| Inclination | 4.102° |
| 253.218° | |
| 129.532° | |
| Physical characteristics | |
| Dimensions | 18.2×10.5×8.9 km |
|
Mean radius
|
6.1 km |
| Mass | 2–3×1016 kg (estimate) |
|
Mean density
|
~2.7 g/cm³ (estimate) |
| ~0.002 m/s² (estimate) | |
| ~0.006 km/s (estimate) | |
| 0.293 d (7.042 h) | |
| Albedo | 0.22 |
| Temperature | ~181 K max: 281 K (+8°C) |
|
Spectral type
|
S |
| 11.46 | |
951 Gaspra /ˈɡæsprə/ 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.
Apart from a multitude of small craters, Gaspra has half a dozen large flat areas and concavities. One of these flat areas, (Dunne Regio), is a 5×7-kilometer area that is flat to within 200 m. It is uncertain whether these are the result of impacts or whether they are instead facets formed when Gaspra broke off its parent asteroid. In the weak, lopsided gravity of Gaspra, impact craters would naturally take on such flat, lopsided shapes, making this determination difficult. The flat facets and concavities give Gaspra a very angular appearance.
Gaspra appears to be fairly olivine-rich among the S-type asteroids (the surface appears to contain olivine and pyroxene in the proportions 4:1 to 7:1). There are no prominent albedo or color patterns, although a subtle color variation is seen across the surface (see image above).
Gaspra's surface lacks unambiguous craters of a size comparable to its radius, like those seen for example on 253 Mathilde. A probable reason is that the collision that produced the Flora family and Gaspra was relatively recent on an astronomical timescale, so that Gaspra has not yet had the opportunity to acquire many large craters since. Analysis of cratering rates suggests the age of the surface is between about 20 to 300 million years.
Grooves about 100–300 m wide, up to 2.5 km long, and tens of meters deep are seen on Gaspra's surface, which may be related to Gaspra's formation along with the rest of the Flora family in an asteroid collision. Their presence also suggest that it is a single coherent body, rather than a rubble pile. The grooves were likely created by impacts that shattered the underlying rock. A system of much more prominent grooves is seen on the Martian moon Phobos. The pitted appearance of some grooves may suggest that the surface is covered by a regolith.
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Wikipedia