Dimorphos
Moon of asteroid Didymos / From Wikipedia, the free encyclopedia
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Dimorphos (formal designation (65803) Didymos I; provisional designation S/2003 (65803) 1) is a natural satellite or moon of the near-Earth asteroid 65803 Didymos, with which it forms a binary system. The moon was discovered on 20 November 2003 by Petr Pravec in collaboration with other astronomers worldwide. Dimorphos has a diameter of 177 meters (581 ft) across its longest extent and it was the target of the Double Asteroid Redirection Test (DART), a NASA space mission that deliberately collided a spacecraft with the moon on 26 September 2022 to alter its orbit around Didymos. Before the impact by DART, Dimorphos had a shape of an oblate spheroid with a surface covered in boulders but virtually no craters.[16] The moon is thought to have formed when Didymos shed its mass due to its rapid rotation, which formed an orbiting ring of debris that conglomerated into a low-density rubble pile that became Dimorphos today.[17][18][19]
Discovery[1] | |
---|---|
Discovered by | Petr Pravec et al.[lower-alpha 1] |
Discovery site | Ondřejov Observatory |
Discovery date | 20 November 2003 |
Designations | |
Designation | Didymos I |
Pronunciation | /daɪˈmɔːrfəs/ |
Named after | Greek word for "having two forms"[2] |
S/2003 (65803) 1 Didymos B "Didymoon" | |
Orbital characteristics[3]: 28 [4] | |
Epoch 26 September 2022 23:14:24.183 UTC (JD 2459849.4683355; impact time)[5]: 5 [3]: 28 | |
1.206±0.035 km (pre-impact)[3]: 28 1.144±0.070 km (post-impact)[6]: 5 | |
Eccentricity | ≈0 (pre-impact)[7]: 15 0.021±0.014[8] or 0.0247±0.0002[9]: 16 (post-impact) |
11.921473±0.000044 hr (11h 55m 17.3s ± 0.2s; pre-impact)[3]: 28 11.3676±0.0014 hr (11h 22m 03.4s ± 5.0s; post-impact)[8] | |
Average orbital speed | 0.177 m/s (pre-impact)[lower-alpha 2] |
Inclination | 169.3°±1.0° with respect to ecliptic[lower-alpha 3] |
Satellite of | 65803 Didymos |
Physical characteristics[5]: 9 | |
Dimensions | 177 × 174 × 116 m (± 2 × 4 × 2 m) |
Mean diameter | 151±5 m (volume equivalent) |
7.58×104 m2[11] | |
Volume | (1.81±0.18)×106 m3 |
Mass | (1.33±0.30)×109 kg (if density is 0.6–0.7 g/cm3)[12] ≈ 4.3×109 kg (if same density as Didymos)[5]: 9 |
Mean density | 0.6–0.7 g/cm3[12] 2.4±0.9 g/cm3 (if same as Didymos)[7]: 29 |
≈ 11.9 hr (synchronous; pre-impact)[13] chaotic (post-impact)[14] | |
Albedo | 0.15±0.02[5]: 6 |
Spectral type | S[15] |
21.4±0.2[1][lower-alpha 4] | |
The DART impact reduced Dimorphos's orbital period around Didymos by 33 minutes and ejected over 1 million kilograms (2.2×10^6 lb) of debris into space, producing a dust plume that temporarily brightened the Didymos system and developed a 10,000-kilometer (6,200 mi)-long dust tail that persisted for several months.[20][21][22] The DART impact is predicted to have caused global resurfacing and deformation of Dimorphos's shape, leaving an impact crater several tens of meters in diameter.[23][15][24] Post-impact observations of brightness fluctuations within the Didymos system suggest that the impact may have either significantly deformed Dimorphos into an ellipsoidal shape or may have sent it into a chaotically tumbling rotation.[8][25] If Dimorphos was in a tumbling rotation state, the moon will be subjected to irregular tidal forces by Didymos before it will eventually return to a tidally locked state within several decades.[14][26][27] The ESA mission Hera is planned to arrive at the Didymos system in 2026 to further study the effects of DART's impact on Dimorphos.