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65803 Didymos (provisional designation 1996 GT) is a sub-kilometer asteroid and binary system that is classified as a potentially hazardous asteroid and near-Earth object of the Apollo group.[lower-alpha 1] The asteroid was discovered in 1996 by the Spacewatch survey at Kitt Peak, and its small 160-metre minor-planet moon, named Dimorphos, was discovered in 2003. Due to its binary nature, the asteroid was then named Didymos, the Greek word for 'twin'.

For other uses, see Didymos.

65803 Didymos
Didymos (bottom left) and Dimorphos (top right) photographed by the DART space probe
Discovery [1]
Discovered bySpacewatch
Discovery siteKitt Peak National Observatory
Discovery date11 April 1996
Designations
MPC designation
(65803) Didymos
Pronunciation/ˈdɪdɪmɒs/[2]
Named after
Greek word for "Twin"[3]
Alternative designations
1996 GT
Minor planet category
NEO · PHA
Apollo (2022) [1][lower-alpha 1]
Orbital characteristics [1]
Epoch 21 January 2022 (JD 2459600.5)
Uncertainty parameter 0
Observation arc24.82 years (9,066 days)
Aphelion2.2753 AU
Perihelion1.0131 AU
Semi-major axis
1.6442 AU
Eccentricity0.38385
Orbital period (sidereal)
2.11 yr (770 days)
Mean anomaly
232.01°
Mean motion
0° 28m 2.28s / day
Inclination3.4079°
Longitude of ascending node
73.196°
Argument of perihelion
319.32°
Known satellitesDimorphos
Earth MOID0.0403 AU (15.7 LD)
Mars MOID0.02 AU (7.8 LD)[4]
Physical characteristics[5]
Dimensions832 m × 838 m × 786 m
Mean radius
390±16 m
or 0.390±0.016 km
Equatorial radius
416±25 m
Polar radius
393±39 m
Surface area
(1.96±0.16)×106 m2
Volume(2.49±0.30)×108 m3
Mass(5.4±0.4)×1011 kg (system)[5]
≈ 5.2×1011 kg (primary)[6]
Mean density
2.17±0.35 g/cm3
Synodic rotation period
2.2600±0.0001[5]
2.2593±0.0002 h[7]
Axial tilt
174°±20°[lower-alpha 2]
Pole ecliptic latitude
−84°±20°
Pole ecliptic longitude
310°±20°
Geometric albedo
0.15±0.04
Spectral type
S[5][9] · SMASS = Xk[1] · X[10]
Absolute magnitude (H)
18.0[1] · 18.16[10][7][11]
18.16±0.03[12]

    Didymos's moon, Dimorphos, was the target of the DART mission to test the viability of asteroid impact avoidance by collision with a spacecraft, while the impact was witnessed by LICIACube, a flyby CubeSat component of the mission.


    Discovery


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

    Didymos was discovered on 11 April 1996 by the University of Arizona Steward Observatory's, and Lunar and Planetary Laboratory's, Spacewatch survey using its 0.9-meter telescope at Kitt Peak National Observatory in Arizona, United States. The binary nature of the asteroid was discovered by others; suspicions of binarity first arose in Goldstone delay-Doppler echoes, and these were confirmed with an optical lightcurve analysis, along with Arecibo radar imaging on 23 November 2003.[4]


    Orbital characteristics


    Didymos orbits the Sun at a distance of 1.0–2.3 AU once every 770 days (2 years and 1 month). Its orbit has an eccentricity of 0.38 and an inclination of 3° with respect to the ecliptic. The minimum distance between the orbit of Earth and the orbit of Didymos is currently 0.04 AU (6.0 million km),[1] but will change as the asteroid is perturbed. In November 2003 it passed 7.18 million km from Earth; it will not come that near again until November 2123, with a distance of 5.86 million km. Didymos also occasionally passes very close to Mars: it will fly by Mars at a distance of 4.68 million km in July 2144.[1] Even the Earth approach of October 2184 is still listed with an uncertainty region of roughly ±1343 km.[13]


    Physical characteristics


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

    In the SMASS classification, Didymos was classified as an Xk-type asteroid, which transitions from the X-type to the rare K-type asteroids.[1] Subsequent visible and near-infrared spectroscopy showed it to be silicate in nature.[14] It rotates rapidly, with a period of 2.26 hours and a brightness variation of 0.08 magnitude (U=3/3), which indicates that the body has a nearly spheroidal shape.[10][7][15][obsolete source]


    Satellite


    Main article: Dimorphos

    Didymos is a binary asteroid with a satellite in its orbit. The minor-planet moon, named Dimorphos,[16] moves in a mostly circular retrograde orbit[17] with an orbital period of 11.9 hours.[10][lower-alpha 3] It measures approximately 160 metres (520 ft) in diameter compared to 780 metres (2,560 ft) for its primary (a mean-diameter-ratio of 0.22).[18] It was previously known by its provisional designation S/2003 (65803) 1 and had been informally called "Didymoon" or "Didymos B".[19][16]


    Naming


    This minor planet was named "Didymos", Greek for "twin", due to its binary nature.[3] The name was suggested by the discoverer, University of Arizona Lunar and Planetary Laboratory astronomer Joseph L. "Joe" Montani, who made the naming proposal to the International Astronomical Union after the binary nature of the object was detected. The approved naming citation was published on 13 July 2004 (M.P.C. 52326).[20]

    The proper name for the satellite Didymos B comes from the word "Dimorphos", Greek for "having two forms".[21] The meaning of the name represents how the form of Dimorphos's orbit will change after the collision with NASA’s Double Asteroid Redirection Test (DART) spacecraft,[16] though in fact the change will be only a very slight change in its orbital parameters. Appropriately, Dimorphos serves dual roles as both a test target and as a part of a blueprint for a modality for future planetary protection.[16] The name of the moon was suggested by planetary scientist Kleomenis Tsiganis at the Aristotle University of Thessaloniki, Greece.[22]


    Exploration


    Artist's impression of the DART spacecraft
    Artist's impression of the DART spacecraft
    Animation of DART's trajectory.mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{}  DART ·   65803 Didymos ·   Earth ·   Sun ·   2001 CB21 ·   3361 Orpheus
    Animation of DART's trajectory
      DART ·   65803 Didymos ·   Earth ·   Sun ·   2001 CB21 ·   3361 Orpheus

    In the early 2010s, Didymos's moon, Dimorphos was to be the principal target of proposed robotic mission by the ESA and NASA, called the Asteroid Impact & Deflection Assessment (AIDA) mission. The ESA dropped out, and the mission did not proceed.[23][24]

    NASA redefined mission requirements and decided to proceed with a 2020s mission to visit Didymos with an impactor, which had been considered as a part of the earlier AIDA mission, named the Double Asteroid Redirection Test or DART. The NASA mission was intended to test whether a spacecraft impact could successfully deflect an asteroid on a collision course with Earth. The DART spacecraft was launched on 24 November 2021, and impacted Dimorphos on September 26, 2022.[25][26][27] It was accompanied by the Italian Space Agency's (ASI) six-unit LICIACube flyby Cubesat that was released 15 days before impact to observe the asteroid and DART's impact.[28]

    DART was the first spacecraft to intentionally target an asteroid known to have a minor-planet moon (243 Ida was visited by the Galileo spacecraft but its moon was unknown until then, and 3548 Eurybates's moon was not discovered until the year when Lucy was due to launch). Didymos is the most easily reachable asteroid of its size from Earth, requiring a delta-v of only 5.1 km/s for a spacecraft to rendezvous, compared to 6.0 km/s to reach the Moon.[29]

    Image of asteroid (65803) Didymos before the DART's impact.
    Image of asteroid (65803) Didymos before the DART's impact.

    After two weeks of analysis, NASA announced that the collision shortened Dimorphos's orbital period around Didymos by 32 minutes,[30] far more than the minimum requirement of 73 seconds and the success benchmark of 10 minutes. The measurement has an uncertainty of ±2 minutes.[31]

    Another mission to Didymos was approved in November 2019 for a planned launch in 2024, to arrive at Didymos in January 2027. ESA's Hera mission is planning to survey the dynamical effects of the DART impact and measure the characteristics of the crater made by DART.[32]


    See also



    Notes


    1. It is an Apollo asteroid because perihelion (q) is less than 1.017 AU (Earth aphelion), not greater.
    2. Naidu et al. (2020) give the Didymos's north pole orientation in terms of ecliptic coordinates, where λ is ecliptic longitude and β is ecliptic latitude.[5]: 12  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.[8] Therefore, given β = –84°, i = 90° – (–84°) = 174° from the ecliptic.
    3. Lightcurve plots of 65803 Didymos, Palmer Divide Observatory, B. D. Warner

    References


    1. "JPL Small-Body Database Browser: 65803 Didymos (1996 GT)" (2017-04-27 last obs.). Jet Propulsion Laboratory. Archived from the original on 22 April 2021. Retrieved 28 June 2017. This article incorporates text from this source, which is in the public domain.
    2. "didymous". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
    3. Schmadel, Lutz D. (2006). "(65803) Didymos [1.64, 0.38, 3.4]". Dictionary of Minor Planet Names – (65803) Didymos, Addendum to Fifth Edition: 2003–2005. Springer Berlin Heidelberg. p. 225. doi:10.1007/978-3-540-34361-5_2677. ISBN 978-3-540-34361-5.
    4. "65803 Didymos (1996 GT)". Minor Planet Center. Archived from the original on 12 November 2020. Retrieved 12 March 2017.
    5. Naidu, S. P.; Benner, L. A. M.; Brozovic, M.; Nolan, M. C.; Ostro, S. J.; Margot, J. L.; et al. (September 2020). "Radar observations and a physical model of binary near-Earth asteroid 65803 Didymos, target of the DART mission" (PDF). Icarus. 348: 113777. Bibcode:2020Icar..34813777N. doi:10.1016/j.icarus.2020.113777. S2CID 219091858. 134777.
    6. Nakano, Ryota; Hirabayashi, Masatoshi; Brozovic, M.; Nolan, M. C.; Ostro, S. J.; Margot, J. L.; et al. (July 2022). "NASA's Double Asteroid Redirection Test (DART): Mutual Orbital Period Change Due to Reshaping in the Near-Earth Binary Asteroid System (65803) Didymos". The Planetary Science Journal. 3 (7): 16. Bibcode:2022PSJ.....3..148N. doi:10.3847/PSJ/ac7566. S2CID 250327233. 148. Archived from the original on 27 September 2022. Retrieved 29 September 2022.
    7. Pravec, P.; Scheirich, P.; Kusnirák, P.; Sarounová, L.; Mottola, S.; Hahn, G.; et al. (March 2006). "Photometric survey of binary near-Earth asteroids". Icarus. 181 (1): 63–93. Bibcode:2006Icar..181...63P. doi:10.1016/j.icarus.2005.10.014. Archived from the original on 3 October 2022. Retrieved 12 March 2017.
    8. "Coordinate transformations". Astronomy and Astrophysics. European Southern Observatory. January 1998. Archived from the original on 17 June 2021. Retrieved 17 June 2022.
    9. 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. Archived from the original on 19 July 2022. Retrieved 28 September 2022.
    10. "LCDB Data for (65803) Didymos". Asteroid Lightcurve Database (LCDB). Archived from the original on 1 July 2020. Retrieved 12 March 2017.
    11. Kitazato, K.; Abe, M.; Mito, H.; Tarusawa, K.; Soyano, T.; Nishihara, S.; et al. (March 2004). "Photometric Behaviour Dependent on Solar Phase Angle and Physical Characteristics of Binary Near-Earth-Asteroid (65803) 1996 GT". 35th Lunar and Planetary Science Conference. p. 1623. Bibcode:2004LPI....35.1623K. Archived from the original on 3 October 2022. Retrieved 12 March 2017.
    12. Pravec, Petr; Harris, Alan W.; Kusnirák, Peter; Galád, Adrián; Hornoch, Kamil (September 2012). "Absolute magnitudes of asteroids and a revision of asteroid albedo estimates from WISE thermal observations". Icarus. 221 (1): 365–387. Bibcode:2012Icar..221..365P. doi:10.1016/j.icarus.2012.07.026. Archived from the original on 8 June 2020. Retrieved 12 March 2017.
    13. "Horizons Batch for 2184-Oct-14 Close Approach". JPL Horizons. Archived from the original on 14 October 2022. Retrieved 14 October 2022. RNG_3sigma = uncertainty range in km. (JPL#194/Soln.date: 2022-Oct-13 generates RNG_3sigma = 1343 km)
    14. de León, J.; Licandro, J.; Serra-Ricart, M.; Pinilla-Alonso, N.; Campins, H. (28 July 2010). "Observations, compositional, and physical characterization of near-Earth and Mars-crosser asteroids from a spectroscopic survey". Astronomy and Astrophysics. 517: A23. doi:10.1051/0004-6361/200913852.
    15. Pravec, P.; Benner, L. A. M.; Nolan, M. C.; Kusnirak, P.; Pray, D.; Giorgini, J. D.; et al. (November 2003). "(65803) 1996 GT". IAU Circulars. 8244 (8244): 2. Bibcode:2003IAUC.8244....2P. Archived from the original on 3 October 2022. Retrieved 12 March 2017.
    16. Talbert, Tricia (23 June 2020). "NASA's First Planetary Defense Mission Target Gets a New Name". NASA. Archived from the original on 10 February 2021. Retrieved 23 June 2020. This article incorporates text from this source, which is in the public domain.
    17. Scheirich, P.; Pravec, P.; Jacobson, S.A.; Ďurech, J.; Kušnirák, P.; Hornoch, K.; Mottola, S.; Mommert, M.; Hellmich, S.; Pray, D.; Polishook, D.; Krugly, Yu.N.; Inasaridze, R.Ya.; Kvaratskhelia, O.I.; Ayvazian, V.; Slyusarev, I.; Pittichová, J.; Jehin, E.; Manfroid, J.; Gillon, M.; Galád, A.; Pollock, J.; Licandro, J.; Alí-Lagoa, V.; Brinsfield, J.; Molotov, I.E. (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.
    18. Johnston, Robert (20 September 2014). "(65803) Didymos". johnstonsarchive.net. Archived from the original on 23 October 2020. Retrieved 28 June 2017.
    19. "Telescopes focus on target of ESA's asteroid mission Archived 18 August 2015 at the Wayback Machine" at phys.org (30 June 2015)
    20. "MPC/MPO/MPS Archive". Minor Planet Center. Archived from the original on 7 January 2022. Retrieved 12 March 2017.
    21. "MPEC 2020-M83 : (65803) Didymos I = Dimorphos". Minor Planet Center. International Astronomical Union. 23 June 2020. Archived from the original on 8 September 2021. Retrieved 23 June 2020.
    22. "IAU Approves Name of Target of First NASA and ESA Planetary Defence Missions". International Astronomical Union. 23 June 2020. Archived from the original on 26 September 2021. Retrieved 23 June 2020.
    23. "AIDA: Asteroid Impact and Deflection Assessment mission under study at ESA and NASA" (PDF). Observatoire de la Côte d'Azur. February 2015. Archived (PDF) from the original on 14 October 2016. Retrieved 28 June 2017.
    24. "Asteroid Impact & Deflection Assessment". ESA. Archived from the original on 19 March 2018. Retrieved 28 June 2017.
    25. Warren, Haygen (26 September 2022). "Brace for impact: DART successfully slams into asteroid". NASASpaceFlight.com. Archived from the original on 27 September 2022. Retrieved 27 September 2022.
    26. "DART Sets Sights on Asteroid Target". NASA. 7 September 2022. Archived from the original on 21 September 2022. Retrieved 20 September 2022.
    27. Potter, Sean (23 November 2021). "NASA, SpaceX Launch DART: First Test Mission to Defend Planet Earth". NASA. Archived from the original on 24 November 2021. Retrieved 25 November 2021.
    28. 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.
    29. "Delta-v for spacecraft rendezvous with all known near-Earth asteroids". 2010. Archived from the original on 3 June 2001. Retrieved 7 October 2010.
    30. "NASA says DART's asteroid impact was a huge success". The Planetary Society. Retrieved 11 October 2022.
    31. "NASA Confirms DART Mission Impact Changed Asteroid's Motion in Space". NASA. Retrieved 11 October 2022.
    32. Numerical modelling of the DART impact and the importance of the Hera mission.[permanent dead link] Sabina D. Raducan, Thomas M. Davison, Gareth S. Collins. PDC 2019. Washington, D.C., USA.



    На других языках

    [de] (65803) Didymos

    (65803) Didymos ist ein erdnaher Doppelasteroid mit seinem Begleiter Dimorphos. Der Asteroid wurde am 11. April 1996 im Rahmen des Spacewatch-Projektes am Kitt Peak National Observatory von Joseph Montani entdeckt. Er hat einen Durchmesser von ca. 800 Metern. Dimorphos wurde 2003 entdeckt, er hat einen Durchmesser von 170 m.
    - [en] 65803 Didymos

    [ru] (65803) Дидим

    (65803) Дидим (др.-греч. Δίδυμος) — небольшой быстро вращающийся околоземный астероид из группы аполлонов, который характеризуется вытянутой орбитой, из-за чего в процессе своего движения вокруг Солнца он пересекает не только орбиту Земли, но и Марса. Астероид был открыт 11 апреля 1996 года в рамках проекта по поиску астероидов Spacewatch в обсерватории Китт-Пик и назван в честь древнегреческого музыкального теоретика Дидима Музыканта.


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