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// Workers AI · dad joke modeWhat did Dactyl say to its moon friend? You're a finger above the rest.

From Wikipedia, the free encyclopedia
(Redirected from Dactyl (asteroid))
Dactyl
Highest-resolution image of Dactyl, recorded while Galileo was about 3,900 km away from the moon
Discovery
Discovered byAnn Harch
Discovery siteGalileo spacecraft
Discovery date17 February 1994
Designations
Pronunciation/ˈdæktɪl/ DAK-til[1]
Named after
Dactyls
1993 (243) 1
AdjectivesDactylian /dækˈtɪliən/[2]
Orbital characteristics
90 km at time of discovery
prograde, ca. 20 h
Inclinationca. 8°[3]
Satellite ofIda
Physical characteristics
Dimensions1.6 km × 1.4 km × 1.2 km
Equatorial escape velocity
0.895 m/s
synchronous
Temperature200 K (−73 °C; −100 °F)

Dactyl (/ˈdæktɪl/ DAK-til), formal designation (243) Ida I, is a small asteroid moon 1,200 by 1,400 by 1,600 m (3,900 by 4,600 by 5,200 ft), in size) that orbits 243 Ida, a main-belt asteroid. It was imaged by the Galileo spacecraft on August 28, 1993; Dactyl was discovered while examining the delayed image downloads from Galileo on February 17, 1994. It was provisionally designated S/1993 (243) 1.[4] The satellite was named after the mythical creatures called dactyls, who, according to Greek mythology, lived on Mount Ida.[5]

Discovery

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Dactyl was found on 17 February 1994 by Galileo mission member Ann Harch, while examining delayed image downloads from the spacecraft.[6] Galileo recorded 47 images of Dactyl over an observation period of 5.5 hours in August 1993.[7] The spacecraft was 10,760 kilometres (6,690 mi) from Ida[8] and 10,870 kilometres (6,750 mi) from Dactyl when the first image of the moon was captured, 14 minutes before Galileo made its closest approach.[9]

Dactyl was initially designated 1993 (243) 1.[8][10] It was named by the International Astronomical Union in 1994,[10] for the mythological Dactyls who inhabited Mount Ida on the island of Crete.[11][12]

Physical characteristics

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Dactyl is an "egg-shaped"[13] but "remarkably spherical"[11] object measuring 1.6 by 1.4 by 1.2 kilometres (0.99 by 0.87 by 0.75 mi).[13] It is oriented with its longest axis pointing towards Ida.[13] Like Ida, Dactyl's surface exhibits saturation cratering.[13] It is marked by more than a dozen craters with a diameter greater than 80 m (260 ft), indicating that the moon has suffered many collisions during its history.[14] At least six craters form a linear chain, suggesting that it was caused by locally produced debris, possibly ejected from Ida.[13] Dactyl's craters may contain central peaks, unlike those found on Ida.[15] These features, and Dactyl's spheroidal shape, imply that the moon is gravitationally controlled despite its small size.[15] Like Ida, its average temperature is about 200 K (−73 °C; −100 °F).[6]

Dactyl shares many characteristics with Ida. Their albedos and reflection spectra are very similar.[16] The small differences indicate that the space weathering process is less active on Dactyl.[17] Its small size would make the formation of significant amounts of regolith impossible.[17][8] This contrasts with Ida, which is covered by a deep layer of regolith.

The two largest imaged craters on Dactyl were named Acmon /ˈækmən/ and Celmis /ˈsɛlmɪs/, after two of the mythological Dactyls. Acmon is the largest crater in the above image, and Celmis is near the bottom of the image, mostly obscured in shadow. The craters are 300 and 200 meters in diameter, respectively.[18]

Orbit

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Diagram of potential orbits of Dactyl around Ida

Dactyl's orbit around Ida is not precisely known. Galileo was in the plane of Dactyl's orbit when most of the images were taken, which made determining its exact orbit difficult.[19] Dactyl orbits in the prograde direction[20] and is inclined about 8° to Ida's equator.[3] Based on computer simulations, Dactyl's pericenter must be more than about 65 km (40 mi) from Ida for it to remain in a stable orbit.[21] The range of orbits generated by the simulations was narrowed down by the necessity of having the orbits pass through points at which Galileo observed Dactyl to be at 16:52:05 UT on 28 August 1993, about 90 km (56 mi) from Ida at longitude 85°.[22][23] On 26 April 1994, the Hubble Space Telescope observed Ida for eight hours and was unable to spot Dactyl. It would have been able to observe it if it were more than about 700 km (430 mi) from Ida.[19]

If in a circular orbit at the distance at which it was seen, Dactyl's orbital period would be about 20 hours.[24] Its orbital speed is roughly 10 m/s (33 ft/s), "about the speed of a fast run or a slowly thrown baseball".[19]

Age and origin

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Dactyl may have originated at the same time as Ida,[25] from the disruption of the Koronis parent body.[26] However, it may have formed more recently, perhaps as ejecta from a large impact on Ida.[27] It is extremely unlikely that it was captured by Ida.[28] Dactyl may have suffered a major impact around 100 million years ago, which reduced its size.[29]

Dactyl was the first asteroid moon discovered. Its discovery settled the long debate over the existence of asteroid moons.

See also

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References

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  1. ↑ "dactyl". Oxford English Dictionary (online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  2. ↑ Edward Coleridge (1990) "The Argonautica" of Apollonius Rhodius, p. 42
  3. 1 2 Petit et al. 1997, p. 177
  4. ↑ Clarke, Aubrey (August 28, 2021). "NASA Galileo Spacecraft Continues to Fulfill Many Tasks After Passing by Asteroid Ida 28 Years Ago". The Space Times.
  5. ↑ "In Depth | 243 Ida". NASA Solar System Exploration. Retrieved 2022-08-11.
  6. 1 2 Holm 1994
  7. ↑ Petit et al. 1997, p. 177
  8. 1 2 3 Belton & Carlson 1994
  9. ↑ Mason 1994, p. 108
  10. 1 2 Green 1994
  11. 1 2 Schmadel 2003, p. 37
  12. ↑ Pausanias & 5.7.6
    When Zeus was born, Rhea entrusted the guardianship of her son to the Dactyls of Ida, who are the same as those called Curetes. They came from Cretan Ida – Heracles, Paeonaeus, Epimedes, Iasius and Idas.
  13. 1 2 3 4 5 Chapman 1996, p. 709
  14. ↑ NASA 2005
  15. 1 2 Asphaug, Ryan & Zuber 2003, p. 463
  16. ↑ Chapman et al. 1994, p. 455
  17. 1 2 Chapman 1995, p. 496
  18. ↑ "Planetary Names: Dactyl". IAU. Archived from the original on 2015-07-01. Retrieved 18 July 2015.
  19. 1 2 3 Byrnes & D'Amario 1994
  20. ↑ Petit et al. 1997, p. 179
  21. ↑ Petit et al. 1997, p. 195
  22. ↑ Petit et al. 1997, p. 188
  23. ↑ Petit et al. 1997, p. 193
  24. ↑ Chapman et al. 1994, p. 455
  25. ↑ Greenberg et al. 1996, p. 116
  26. ↑ Lee et al. 1996, p. 97
  27. ↑ Petit et al. 1997, p. 182
  28. ↑ Mason 1994, p. 108
  29. ↑ Greenberg et al. 1996, p. 117

Works cited

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