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Dimorphos

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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]
Satellite of65803 Didymos
Physical characteristics[1]
0.170±0.030 km
or 170±30 m
21.3±0.2 (difference from primary)[1]

Dimorphos is a small satellite of an asteroid that was discovered in 2003. It is the minor-planet moon of a synchronous binary system with 65803 Didymos as the primary asteroid. After being provisionally designated as S/2003 (65803) 1 with informal nicknames such as "Didymos B" and "Didymoon", the Working Group Small Body Nomenclature (WGSBN) of the International Astronomical Union gave the satellite its official name on 23 June 2020.[3] At a diameter of 170 metres (560 ft), it is one of the smallest astronomical objects that has been given a permanent name.[2]

Dimorphos was the target of NASA's Double Asteroid Redirection Test (DART), a mission spacecraft which was launched on 24 November 2021 and impacted on 27 September 2022. The DART mission is a test of planetary defense against asteroids.[4] A flyby mini-satellite named LICIACube, provided by the Italian Space Agency, photographed the collision.

The European Space Agency's Hera mission will observe the asteroid 4 years after the impact.[5]

Discovery

The primary asteroid was discovered in 1996 by Joe Montani of the Spacewatch Project at the University of Arizona. The name Didymos was officially approved in 2004.[1] Petr Pravec of the Ondřejov Observatory in the Czech Republic found in 2003 that the asteroid had a satellite orbiting it. With his collaborators, he confirmed from the Arecibo radar delay-Doppler images that Didymos is a binary system.[6]

Naming

The name is derived from a Greek word Dimorphos (Δίμορφος) meaning "having two forms".[7][8][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.[9]

Characteristics

Shape model of Didymos and its satellite Dimorphos, based on photometric lightcurve and radar data

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).[10]

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.[11]

Dimorphos measures approximately 170 metres (560 ft) in diameter, compared to Didymos which is 780 metres (2,560 ft) across.[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]

DART is the first experiment for defending Earth from hazardous asteroids, and the spacecraft will try to deflect Dimorphos slightly from its position.[14] The spacecraft is expected to crash into Dimorphos at a speed of around 15,000 mph (6.6 km/s)[14] between 26 September and 1 October 2022.[15] The collision is expected to bring Dimorphos and Didymos closer to each other.[3][16] Dimorphos will then circle Didymos faster than before, so that its orbit is shortened by at least 10 minutes.[14][3]

The DART spacecraft is accompanied by LICIACube, a flyby Cubesat of the Italian Space Agency (ASI) 6 Unit to record the collision, that was released 15 days before impact.[13][17] Then the European Space Agency will launch its Hera spacecraft to Dimorphos in 2024 to study the impact crater and the new orbit of the binary system.[16]

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. ^ 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.
  4. ^ Potter, Sean (23 November 2021). "NASA, SpaceX Launch DART: First test mission to defend planet Earth". NASA (Press release). Retrieved 25 November 2021.
  5. ^ 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.
  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. ^ "MPEC 2020-M83". minorplanetcenter.net. Cambridge, MA: Minor Planet Center. Retrieved 1 July 2020.
  8. ^ δίμορφος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  9. ^ "Target: Didymoon". esa.int. European Space Agency. 31 March 2015. Retrieved 24 November 2021.
  10. ^ 65803 Didymos (Report). JPL Small-Body Database Browser. NASA / Jet Propulsion Laboratory. Retrieved 30 December 2021 – via ssd.jpl.nasa.gov.
  11. ^ 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.
  12. ^ "(65803) Didymos". johnstonsarchive.net. Retrieved 1 July 2020.
  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. ^ 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.
  15. ^ 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.
  16. ^ 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.
  17. ^ "DART's small satellite companion tests camera prior to Dimorphos impact". NASA.gov (Press release). National Aeronautics and Space Administration. Retrieved 25 September 2022.
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