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== Discovery ==
== Discovery ==
The primary asteroid Didymos was discovered in 1996 by Joe Montani of the [[Spacewatch Project]] at the University of Arizona.<ref name=johnston>{{cite web |title=(65803) Didymos |website=www.johnstonsarchive.net |url=http://www.johnstonsarchive.net/astro/astmoons/am-65803.html |access-date=2021-11-11}}</ref> The satellite Dimorphos was discovered on 20 November 2003, in [[photometry (astronomy)|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 [[eclipse]]s and [[occultation (astronomy)|occultations]]. With his collaborators, he confirmed from the Arecibo radar delay-Doppler images that Didymos is a binary system.<ref>{{cite report |last1=Pravec |first1=P. |last2=Benner |first2=L.A.M. |last3=Nolan|first3=M.C. |last4=Kusnirak |first4=P. |last5=Pray |first5=D. |last6=Giorgini |first6=J. D.|last7=Jurgens |first7=R.F. |last8=Ostro |first8=S.J. |last9=Margot |first9=J.-L. |last10=Magri |first10=C. |last11=Grauer |first11=A. |year=2003 |title={{nobr|(65803) 1996 GT}} |lang=en |series=[[IAU Circular]] |volume=8244 |page=2 |bibcode=2003IAUC.8244....2P |publisher=[[International Astronomical Union]] / [[Central Bureau for Astronomical Telegrams]] |place=Cambridge, MA |via=[[Harvard University|Harvard U.]] |url=https://ui.adsabs.harvard.edu/abs/2003IAUC.8244....2P/abstract}}</ref>
The primary asteroid Didymos was discovered in 1996 by Joe Montani of the [[Spacewatch Project]] at the University of Arizona.<ref name=johnston>{{cite web |title=(65803) Didymos |website=www.johnstonsarchive.net |url=http://www.johnstonsarchive.net/astro/astmoons/am-65803.html |access-date=2021-11-11}}</ref> The satellite Dimorphos was discovered on 20 November 2003, in [[photometry (astronomy)|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 [[eclipse]]s and [[occultation (astronomy)|occultations]]. With his collaborators, he confirmed from the [[Arecibo Observatory|Arecibo radar delay-Doppler]] images that Didymos is a binary system.<ref>{{cite report |last1=Pravec |first1=P. |last2=Benner |first2=L.A.M. |last3=Nolan|first3=M.C. |last4=Kusnirak |first4=P. |last5=Pray |first5=D. |last6=Giorgini |first6=J. D.|last7=Jurgens |first7=R.F. |last8=Ostro |first8=S.J. |last9=Margot |first9=J.-L. |last10=Magri |first10=C. |last11=Grauer |first11=A. |year=2003 |title={{nobr|(65803) 1996 GT}} |lang=en |series=[[IAU Circular]] |volume=8244 |page=2 |bibcode=2003IAUC.8244....2P |publisher=[[International Astronomical Union]] / [[Central Bureau for Astronomical Telegrams]] |place=Cambridge, MA |via=[[Harvard University|Harvard U.]] |url=https://ui.adsabs.harvard.edu/abs/2003IAUC.8244....2P/abstract}}</ref>


== Naming ==
== Naming ==

Revision as of 14:52, 27 September 2022

Dimorphos
Dimorphos in September 2022, prior to 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[1]
1.19±0.03 km
Eccentricity< 0.05
0.4971±0.0004 d
or 11.93±0.01 hr[b]
0.174 m/s
Satellite of65803 Didymos
Physical characteristics[1]
0.170±0.030 km
or 170±30 m
Mass~ 5×109 kg [3]
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). Discovered in 2003 at the Ondřejov Observatory, it was the target of the NASA/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. ESA's Hera will arrive at the Didymos system in 2026 to further study the effects of the impact on the moon.

Discovery

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.[4]

Naming

The Working Group Small Body Nomenclature of the International Astronomical Union (IAU) gave the satellite its official name on 23 June 2020.[5] The name is derived from a Greek word Dimorphos (Δίμορφος) meaning "having two forms".[6][7][c] 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.[8]

Characteristics

Penultimate image of Dimorphos' surface by DART

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).[9]

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.[10]

Dimorphos measures approximately 170 metres (560 ft) in diameter, compared to Didymos which is 780 metres (2,560 ft) across.[11] 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 surface features that had never been seen before. Tariq Malik of Space.com described it as "covered in boulders and uneven terrain".[12]

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.[13][14]

DART is the first experiment for defending Earth from hazardous asteroids, and the spacecraft tried to deflect Dimorphos slightly from its position.[15] The spacecraft crashed into Dimorphos at a speed of around 15,000 mph (6.6 km/s)[15] on 26 September.[16] The collision is expected to bring Dimorphos and Didymos closer to each other.[5][17] Dimorphos will then circle Didymos faster than before, so that its orbit is shortened by at least 10 minutes.[15][5]

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.[13][18] 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.[17][19]

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. ^ 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 e f "(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. ^ https://dart.jhuapl.edu/Mission/index.php
  4. ^ 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.
  5. ^ 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.
  6. ^ "MPEC 2020-M83". minorplanetcenter.net. Cambridge, MA: Minor Planet Center. Retrieved 1 July 2020.
  7. ^ δίμορφος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  8. ^ "Target: Didymoon". esa.int. European Space Agency. 31 March 2015. Retrieved 24 November 2021.
  9. ^ 65803 Didymos (Report). JPL Small-Body Database Browser. NASA / Jet Propulsion Laboratory. Retrieved 30 December 2021 – via ssd.jpl.nasa.gov.
  10. ^ 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.
  11. ^ "(65803) Didymos". johnstonsarchive.net. Retrieved 1 July 2020.
  12. ^ Tariq Malik (26 September 2022). "NASA crashes DART spacecraft into asteroid in world's 1st planetary defense test". Space.com.
  13. ^ 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.
  14. ^ Potter, Sean (23 November 2021). "NASA, SpaceX Launch DART: First test mission to defend planet Earth". NASA (Press release). Retrieved 25 November 2021.
  15. ^ 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.
  16. ^ 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.
  17. ^ 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.
  18. ^ "DART's small satellite companion tests camera prior to Dimorphos impact". NASA.gov (Press release). National Aeronautics and Space Administration. Retrieved 25 September 2022.
  19. ^ Witze, Alexandra (19 November 2021). "NASA spacecraft will slam into asteroid in first planetary-defence test". Nature. No. 7887. pp. 17–18. doi:10.1038/d41586-021-03471-w. PMID 34799719. S2CID 244428237.
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