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'''(65803) Didymos I Dimorphos''' ([[provisional designation]] '''S/2003 (65803) 1''') is a [[minor-planet moon]] of the [[near-Earth object|near-Earth asteroid]] [[65803 Didymos]], with which it shares a [[Binary asteroid|binary system]]. It has a diameter of {{convert|170|m|ft}}. Discovered in 2003 at the [[Ondřejov Observatory]], it was the target of the [[NASA]]/[[Johns Hopkins University Applied Physics Laboratory|JHUAPL]] [[Double Asteroid Redirection Test]] (DART), which sent an impactor to alter the moon's orbit around Didymos by colliding with it on September 26, 2022. [[European Space Agency|ESA]]'s ''[[Hera (space mission)|Hera]]'' will arrive at the Didymos system in 2026 to further study the effects of the impact on the moon.
'''(65803) Didymos I Dimorphos''' ([[provisional designation]] '''S/2003 (65803) 1''') is a [[minor-planet moon]] of the [[near-Earth object|near-Earth asteroid]] [[65803 Didymos]], with which it shares a [[Binary asteroid|binary system]]. It has a diameter of {{convert|170|m|ft}}, and has been characterised as a low-density [[rubble pile]]. Discovered in 2003 at the [[Ondřejov Observatory]], it was the target of the [[Double Asteroid Redirection Test]] (DART), which deliberately collided a spacecraft with the moon in September 2022 to alter the moon's orbit around Didymos. ''[[Hera (space mission)|Hera]]'' will arrive at the Didymos system in 2026 to further study the effects of the collision on the moon.


== Discovery ==
== Discovery ==

Revision as of 17:09, 28 September 2022

Dimorphos
File:Dimorphos composite.jpg
Dimorphos in September 2022, seconds before the impact of DART
Discovery[1]
Discovered byPravec et al.[a]
Discovery date20 November 2003
Designations
Designation
Didymos I
Pronunciation/daɪˈmɔːrfəs/
Named after
Greek word for "having two forms"[2]
S/2003 (65803) 1
Orbital characteristics[3]
Epoch 7.5 November 2011 (JD 2455873.0)
1.19±0.03 km
Eccentricity≤ 0.03
11.921624±0.000018 hr[b]
or 0.496734 d
0.174 m/s
89.1°
Inclination168.6°±1.8° wrt ecliptic[c]
Satellite of65803 Didymos
Physical characteristics[3]
171±11 m[3]
or 0.171±0.011 km
Mass~ 5×109 kg[5]
synchronous?
Albedo0.15±0.04
Spectral type
S
21.3±0.2 (difference from primary)[1]

(65803) Didymos I Dimorphos (provisional designation S/2003 (65803) 1) is a minor-planet moon of the near-Earth asteroid 65803 Didymos, with which it shares a binary system. It has a diameter of 170 metres (560 ft), and has been characterised as a low-density rubble pile. Discovered in 2003 at the Ondřejov Observatory, it was the target of the Double Asteroid Redirection Test (DART), which deliberately collided a spacecraft with the moon in September 2022 to alter the moon's orbit around Didymos. Hera will arrive at the Didymos system in 2026 to further study the effects of the collision on the moon.

Discovery

Radar images of Didymos and Dimorphos taken by the Arecibo Observatory in 2003

The primary asteroid Didymos was discovered in 1996 by Joe Montani of the Spacewatch Project at the University of Arizona.[1] The satellite Dimorphos was discovered on 20 November 2003, in photometric observations by Petr Pravec and colleagues at the Ondřejov Observatory in the Czech Republic. Dimorphos was detected through periodic dips in Didymos's brightness due to mutual eclipses and occultations. With his collaborators, he confirmed from the Arecibo radar delay-Doppler images that Didymos is a binary system.[6]

Naming

The Working Group Small Body Nomenclature of the International Astronomical Union (IAU) gave the satellite its official name on 23 June 2020.[7] The name is derived from a Greek word Dimorphos (Δίμορφος) meaning "having two forms".[8][9][d] The justification for the new name reads: "As the target of the DART and Hera space missions, it will become the first celestial body in cosmic history whose form was substantially changed as a result of human intervention (the DART impact)".[2]

Prior to the IAU naming, the nickname "Didymoon" was used in official communications.[10]

Characteristics

Surface of Dimorphos, captured by DART two seconds before impact.

The primary body of the binary system, Didymos, orbits the Sun at a distance of 1.0–2.3 AU once every 770 days (2 years and 1 month). The pathway of the orbit has an eccentricity of 0.38 and an inclination of 3° with respect to the ecliptic. On 4 October 2022 Didymos will make an Earth approach of 10.6 million km (6.6 million mi).[11]

Dimorphos moves in a nearly equatorial, nearly circular orbit around Didymos, with an orbital period of 11.9 hours. Its orbit period is synchronous with its rotation, so that the same side of Dimorphos always faces Didymos. Dimorphos's orbit is retrograde relative to the ecliptic plane, in conformity with Didymos's retrograde rotation.[12]

Dimorphos measures approximately 170 metres (560 ft) in diameter, compared to Didymos which is 780 metres (2,560 ft) across.[13] It is currently the smallest celestial object given a formal name by the IAU.[2]

The final few minutes of pictures from the DART mission revealed an egg-shaped body covered with boulders, clearly indicating it has a rubble pile structure.[14][15] Preliminary LICIACube images of the impact revealed a filamentary plume of dusty ejecta expanding outward from Dimorphos.[16][17] Astronomers using telescopes from Earth as well as the Hubble Space Telescope, James Webb Space Telescope, and the Lucy spacecraft detected significant brightening of the Didymos system as the ejecta plume expanded in a crescent shape.[18]

Exploration

On 24 November 2021, NASA launched the Double Asteroid Redirection Test (DART) spacecraft on a SpaceX Falcon 9 rocket from Space Launch Complex 4 East at Vandenberg Space Force Base in California, US.[19][20]

DART is the first experiment for defending Earth from hazardous asteroids, and the spacecraft tried to deflect Dimorphos slightly from its position.[21] The spacecraft crashed into Dimorphos at a speed of around 15,000 mph (6.6 km/s)[21] on 26 September.[22] The collision is expected to bring Dimorphos and Didymos closer to each other.[7][23] Dimorphos will then circle Didymos faster than before, so that its orbit is shortened by at least 10 minutes.[21][7]

The DART spacecraft is accompanied by LICIACube, a flyby Cubesat of the Italian Space Agency (ASI) 6 Unit, released 15 days before impact to record the collision.[19][24] The European Space Agency plans to launch the Hera spacecraft to Dimorphos in 2024 to study the impact crater and the new orbit of the binary system.[23][25]

Footnotes

  1. ^ Astronomers involved in the discovery of Dimorphos include P. Pravec, L.A.M. Benner, M.C. Nolan, P. Kusnirak, D. Pray, J.D. Giorgini, R.F. Jurgens, S.J. Ostro, J.-L. Margot, C. Magri, A. Grauer, and S. Larson. The discovery used lightcurve and radar observations from the Jet Propulsion Laboratory, Pasadena, CA; National Astronomy and Ionosphere Center / Arecibo Observatory, Arecibo, PR; and Ondrejov Observatory, Ondřejov, CZ. [1]
  2. ^ before the impact of DART
  3. ^ Scheirich and Pravec (2022) give the Dimorphos's orbit pole orientation in terms of ecliptic coordinates, where λ is ecliptic longitude and β is ecliptic latitude.[3]: 4  β is the angular offset from the ecliptic plane whereas inclination i with respect to the ecliptic is the angular offset from the ecliptic north pole at β = +90°; i with respect to the ecliptic would be the complement of β.[4] Therefore, given β = –78.6°, i = 90° – (–78.6°) = 168.6° from the ecliptic.
  4. ^ The name "Δίμορφος" was suggested by planetary scientist Kleomenis Tsiganis at the Aristotle University of Thessaloniki. Tsiganis explained that the name "has been chosen in anticipation of its changes: It will be known to us in two very different forms, the one seen by DART before the impact, and the other seen by Hera a few years later".[2]

References

  1. ^ a b c d "(65803) Didymos". www.johnstonsarchive.net. Retrieved 11 November 2021.
  2. ^ a b c d "IAU approves name of target of first NASA and ESA planetary defence missions". iau.org (Press release). International Astronomical Union. 23 June 2020. Retrieved 1 July 2020.
  3. ^ a b c d Scheirich, P.; Pravec, P. (July 2022). "Preimpact Mutual Orbit of the DART Target Binary Asteroid (65803) Didymos Derived from Observations of Mutual Events in 2003–2021". The Planetary Science Journal. 3 (7): 12. Bibcode:2022PSJ.....3..163S. doi:10.3847/PSJ/ac7233. S2CID 250650906. 163.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  4. ^ "Coordinate transformations". Astronomy and Astrophysics. European Southern Observatory. January 1998. Archived from the original on 17 June 2021. Retrieved 17 June 2022.
  5. ^ "DART".
  6. ^ Pravec, P.; Benner, L.A.M.; Nolan, M.C.; Kusnirak, P.; Pray, D.; Giorgini, J. D.; Jurgens, R.F.; Ostro, S.J.; Margot, J.-L.; Magri, C.; Grauer, A. (2003). (65803) 1996 GT (Report). IAU Circular. Vol. 8244. Cambridge, MA: International Astronomical Union / Central Bureau for Astronomical Telegrams. p. 2. Bibcode:2003IAUC.8244....2P – via Harvard U.
  7. ^ a b c Temming, Maria (29 June 2020). "An asteroid's moon got a name so NASA can bump it off its course". Science News. Retrieved 1 July 2020.
  8. ^ "MPEC 2020-M83". minorplanetcenter.net. Cambridge, MA: Minor Planet Center. Retrieved 1 July 2020.
  9. ^ δίμορφος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  10. ^ "Target: Didymoon". esa.int. European Space Agency. 31 March 2015. Retrieved 24 November 2021.
  11. ^ 65803 Didymos (Report). JPL Small-Body Database Browser. NASA / Jet Propulsion Laboratory. Retrieved 30 December 2021 – via ssd.jpl.nasa.gov.
  12. ^ Scheirich, P.; Pravec, P.; Jacobson, S.A.; Ďurech, J.; Kušnirák, P.; Hornoch, K.; et al. (2015). "The binary near-Earth asteroid (175706) 1996 FG3 – an observational constraint on its orbital evolution". Icarus. 245: 56–63. arXiv:1406.4677. Bibcode:2015Icar..245...56S. doi:10.1016/j.icarus.2014.09.023. S2CID 119248574.
  13. ^ "(65803) Didymos". johnstonsarchive.net. Retrieved 1 July 2020.
  14. ^ Tariq Malik (26 September 2022). "NASA crashes DART spacecraft into asteroid in world's 1st planetary defense test". Space.com.
  15. ^ Savitsky, Zack (27 September 2022). "'Holy $@*%!' Science captures behind-the-scenes reactions to asteroid-smashing mission". Science. Retrieved 28 September 2022.
  16. ^ Witze, Alexandra (27 September 2022). "Fresh images reveal fireworks when NASA spacecraft plowed into asteroid". Nature. doi:10.1038/d41586-022-03067-y. Retrieved 28 September 2022.
  17. ^ Paoletta, Rae (26 September 2022). "See DART's final images before it smashed into an asteroid". The Planetary Society. Retrieved 28 September 2022.
  18. ^ Lakdawalla, Emily (27 September 2022). "Photos Show Drama of DART Asteroid Impact". Sky & Telescope. Retrieved 28 September 2022.
  19. ^ a b Greshko, Michael (23 November 2021). "This NASA spacecraft will smash into an asteroid – to practice saving Earth". National Geographic. Archived from the original on 23 November 2021. Retrieved 25 November 2021.
  20. ^ Potter, Sean (23 November 2021). "NASA, SpaceX Launch DART: First test mission to defend planet Earth". NASA (Press release). Retrieved 25 November 2021.
  21. ^ a b c Rincon, Paul (24 November 2021). "NASA DART asteroid spacecraft: Mission to smash into Dimorphos space rock launches". BBC News. Retrieved 25 November 2021.
  22. ^ Potter, Sean (23 November 2021). "NASA, SpaceX Launch DART: First test mission to defend planet Earth". NASA (Press release). National Aeronautics and Space Administration. Retrieved 25 November 2021.
  23. ^ a b Crane, Leah (23 November 2021). "NASA's DART mission will try to deflect an asteroid by flying into it". New Scientist. Archived from the original on 23 November 2021. Retrieved 25 November 2021.
  24. ^ "DART's small satellite companion tests camera prior to Dimorphos impact". NASA.gov (Press release). National Aeronautics and Space Administration. Retrieved 25 September 2022.
  25. ^ Witze, Alexandra (19 November 2021). "NASA spacecraft will slam into asteroid in first planetary-defence test". Nature (7887): 17–18. doi:10.1038/d41586-021-03471-w. PMID 34799719. S2CID 244428237.
  • Media related to Dimorphos at Wikimedia Commons
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