2020 CD3

2020 CD3 is a tiny near-Earth asteroid and temporary satellite of Earth. It was discovered at the Mount Lemmon Observatory by astronomers Theodore Pruyne and Kacper Wierzchoś on 15 February 2020, as part of the Mount Lemmon Survey or Catalina Sky Survey. The asteroid's discovery was announced by the Minor Planet Center on 25 February 2020, after subsequent observations have confirmed that it is orbiting around Earth. It is the second temporary satellite of Earth discovered in situ, after 2006 RH120, which was discovered in 2006. Based on its nominal trajectory, 2020 CD3 was captured by Earth between 2015–2016, and has likely escaped Earth's gravitational sphere of influence around May 2020.[5][10] 2020 CD3 will make another close pass to Earth in March 2044, though it will most likely not be captured by Earth due to the greater approach distance.[11][12]

2020 CD3
2020 CD3 imaged in color by Gemini North
Discovery [1][2]
Discovered byMt. Lemmon Survey
Discovery siteMt. Lemmon Obs. (CSS)
Discovery date15 February 2020
Designations
2020 CD3
C26FED2 [3][4]
NEO · Arjuna [5] · Apollo [6]
temporarily captured [1] · co-orbital [5]
Orbital characteristics [6]
Epoch 1 March 2020 (JD 2458909.5)
Uncertainty parameter 2
Observation arc36 days
Aphelion1.0647 AU
Perihelion0.9860 AU
1.0253 AU
Eccentricity0.03838
1.04 yr (379.2 d)
39.719°
0° 56m 57.582s / day
Inclination0.8447°
138.574°
339.620°
Earth MOID0.00175554 AU
Physical characteristics
Mean diameter
1.9–3.5 m (est.)[7]
2 m (est.)[8]
Mass~4900 kg (est.)[8]
24.0[9]
31.672±0.340[6]
31.7[2]

    2020 CD3 has an absolute magnitude around 32, indicating that it is very small in size. Assuming that 2020 CD3 has a low albedo characteristic of dark, carbonaceous C-type asteroids, its diameter is probably around 1.9–3.5 metres (6–11 ft).[13][14] 2020 CD3 is classified as an Arjuna asteroid, a subtype of small Earth-crossing Apollo asteroids that have Earth-like orbits.[5]

    Discovery
    Color composite image of 2020 CD3 obtained by the Gemini Observatory on 24 February 2020[7]

    2020 CD3 was discovered on 15 February 2020, by astronomers Theodore Pruyne and Kacper Wierzchos at the Mount Lemmon Observatory. The discovery formed part of the Mount Lemmon Survey designed for discovering near-Earth objects, which is also part of the Catalina Sky Survey conducted at Tucson, Arizona.[1][7] 2020 CD3 was found as a faint, 20th magnitude object in the constellation of Virgo, located about 0.0019 AU (280,000 km; 180,000 mi) from Earth at the time.[15][16][lower-alpha 1] The observed orbital motion of the object suggested that it may be gravitationally bound to Earth, which prompted further observations to secure and determine its motion.[4]

    The object's discovery was reported to the Minor Planet Center's Near-Earth Object Confirmation Page (NEOCP), where a preliminary orbit was calculated from additional observations conducted at several observatories.[4] Follow-up observations of 2020 CD3 spanned six days since its discovery, and the object was formally announced in a Minor Planet Electronic Circular notice issued by the Minor Planet Center on 25 February 2020. No indication of perturbations by solar radiation pressure was observed, and 2020 CD3 could not be linked to any known artificial object.[1] Although the evidence implied that 2020 CD3 is most likely a dense, rocky asteroid, the possibility of the object being artificial has not yet been fully ruled out.[17][16]

    As of February 2020, no precovery images of 2020 CD3 have been identified.[6] The discoverers of 2020 CD3 have suspected that it is possible that the object may have been imaged by other astronomical surveys prior to its discovery, but had not been identified due to its faintness and highly variable orbit.[17]

    Nomenclature

    Upon discovery, the asteroid was given the temporary internal designation C26FED2.[4][3] After follow up observations confirming the object, it was then given the provisional designation 2020 CD3 by the Minor Planet Center on 25 February 2020.[1] The provisional designation signifies the object's discovery date and year. The object has not yet been issued a permanent minor planet number by the Minor Planet Center due to its short observation arc of several days.[18]

    Orbit
    Animation of 2020 CD3's orbit around Earth
      2020 CD3 ·   Moon ·   Earth

    Prior to the temporary capture of 2020 CD3, its heliocentric orbit was probably Earth-crossing, either falling into the categories of an Aten-type orbit (a < 1 AU) or an Apollo-type orbit (a > 1 AU), with the former considered to be more likely.[5]

    Temporary capture
    The orbit of 2020 CD3 around the Earth. The white band is the orbit of the Moon.
    Trajectory and orbits of 2020 CD3 around Earth, from 2015–2020.[lower-alpha 2]
    (click image to see spin view)

    Because 2020 CD3 has an Earth-like heliocentric orbit, its motion relative to Earth is low, allowing for it to slowly approach the planet and get captured.[5] Nominal orbit solutions for 2020 CD3 suggest that it was captured by Earth between 2015–2016, and is expected to leave its geocentric orbit by May 2020 according to simulations of its orbit.[5] The geocentric orbit of 2020 CD3 is chaotic due to the combined effects of tidal forces from the Sun and Earth as well as repeated close encounters with the Moon.[19][17] The Moon gravitationally perturbs 2020 CD3's geocentric orbit, causing it to be unstable. Over the course of 2020 CD3's orbit around Earth, repeated close encounters with the Moon will eventually lead to ejection from its geocentric orbit as the Moon's perturbations can transfer enough momentum for 2020 CD3 to escape Earth's gravitational influence.[20][19][21]

    2020 CD3's orbit around Earth is highly variable and eccentric, hence predictions of its past trajectory are uncertain.[14][21] According to the JPL Small-Body Database, the closest approach to Earth has already occurred, on 4 April 2019, when it approached to a distance of 13,121 km (8,153 mi).[6][lower-alpha 3] The previous close approach by 2020 CD3 had occurred on 13 February 2020, at a distance of about 41,000 km (25,000 mi) from Earth's surface.[21] The orbital period of 2020 CD3 around Earth is currently around 47 days,[17] though on larger orbits around Earth, 2020 CD3's orbital period can range from 70 to 90 days.[21] However, these estimates are very uncertain due to the chaotic dynamics of 2020 CD3's orbit.[21]

    Being captured into a temporary orbit around Earth, 2020 CD3 is a temporarily captured object or a temporary satellite of Earth.[1][22] 2020 CD3 has also been widely referred to in the media as a "mini-moon" of Earth, due to its small size.[7][13][14][23] 2020 CD3 is the second known temporary captured object discovered in situ around Earth, with the first being 2006 RH120, which was discovered in 2006.[23] Other objects have also been suspected to have once been temporarily captured, including the small near-Eath asteroid 1991 VG and the bolide DN160822 03.[24][25] Objects that get temporarily captured by Earth are thought to be common, though larger objects over 0.6 m (2 ft) in diameter are believed to be less likely to be captured by Earth and detected by modern telescopes.[23]

    Future approaches

    After its departure from Earth, 2020 CD3 will continue orbiting the Sun and will approach Earth in March 2044, from a nominal distance of 0.0245 AU (3.67 million km; 2.28 million mi). Accounting for uncertainties in its orbit, the minimum approach distance from Earth is expected to be 0.0237 AU (3.55 million km; 2.20 million mi).[11] It is unlikely that 2020 CD3 will be captured by Earth in the March 2044 encounter, as the approach distance is too large for capture.[12] Assuming that 2020 CD3's orbit does not change after the 2044 close approach, the next encounter would be around 2061, when it is expected to approach Earth from a nominal distance of 0.0375 AU (5.61 million km; 3.49 million mi). However, uncertainties in the 2061 approach distance are greater; 2020 CD3's minimum approach distance could be 0.0131 AU (1.96 million km; 1.22 million mi).[11]

    The possibility of 2020 CD3 impacting Earth has been considered by the Jet Propulsion Laboratory's Sentry risk table.[8] Being only a few meters in size, an impact by 2020 CD3 would pose no significant threat to Earth as it would most likely fragment and disintegrate upon atmospheric entry.[16] Because of the minimal impact hazard of 2020 CD3, it is given a Torino Scale rating of 0 and a cumulative Palermo Scale rating of –5.22.[8] Over a period of 100 years from the present, the cumulative impact probability of 2020 CD3 is estimated to be 0.022%. Within this time frame, the date with the highest probability of impact is probably 14 September 2061, which is estimated to have an impact probability of 0.0073% and a negligible Palermo Scale rating of –5.55.[8]

    Physical characteristics

    2020 CD3 is estimated to have an absolute magnitude (H) around 31.7, indicating that it is very small in size.[6] The rotation period and albedo of 2020 CD3 have not been measured due to the limited number of observations.[17] Assuming that the albedo of 2020 CD3 is similar to those of dark, carbonaceous C-type asteroids, the diameter of 2020 CD3 is around 1.9–3.5 m (6–11 ft), comparable to in size to that of a small car.[14][22] The JPL Sentry risk table estimates 2020 CD3 to have a mass of 4,900 kg (10,800 lb), based on the assumption that the asteroid has a diameter of 2 m (6.6 ft).[8]

    See also

    Notes
    1. The celestial coordinates of 2020 CD3 at the time of discovery were  13h 03m 33.11s +09° 10′ 43.1″.[1] See Virgo for constellation coordinates.
    2. JPL Horizons 28 Feb 2020 solution[6]
    3. 2020 CD3's 4 April 2019 close approach distance from Earth listed as 8.77114878745299×10−5 AU on the JPL Small-Body Database.[6]

    References
    1. "MPEC 2020-D104 : 2020 CD3: Temporarily Captured Object". Minor Planet Electronic Circular. Minor Planet Center. 25 February 2020. Retrieved 25 February 2020.
    2. "2020 CD3". Minor Planet Center. International Astronomical Union. Retrieved 25 February 2020.
    3. "2020 CD3". NEO Exchange. Las Cumbres Observatory. 15 February 2020. Retrieved 25 February 2020.
    4. ""Pseudo-MPEC" for C26FED2". Project Pluto. 24 February 2020. Retrieved 25 February 2020.
    5. de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (7 April 2020). "On the orbital evolution of meteoroid 2020 CD3, a temporarily captured orbiter of the Earth-Moon system". Monthly Notices of the Royal Astronomical Society. 494 (1): 1089–1094. arXiv:2003.09220. Bibcode:2020MNRAS.494.1089D. doi:10.1093/mnras/staa809.
    6. "JPL Small-Body Database Browser: 2020 CD3" (2020-03-22 last obs.). Jet Propulsion Laboratory. Retrieved 25 February 2020.
    7. "Gemini Telescope Images "Minimoon" Orbiting Earth — in Color!". National Optical-Infrared Astronomy Research Laboratory (Press release). National Science Foundation. 27 February 2020. Retrieved 28 February 2020.
    8. "2020 CD3 -- Earth Impact Risk Summary". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 3 March 2020.
    9. "2020CD3". Near Earth Objects – Dynamic Site. Department of Mathematics, University of Pisa, Italy. Retrieved 25 February 2020.
    10. Taylor Redd, Nola (9 April 2020). "Is Earth's Minimoon Still Here?". Sky & Telescope. Retrieved 9 May 2020.
    11. "2020CD3 Close Approaches". Near Earth Objects – Dynamic Site. Department of Mathematics, University of Pisa, Italy. Retrieved 1 March 2020.
    12. Koren, Marina (20 March 2020). "A Fleeting Moment in the Solar System". The Atlantic. Retrieved 2 April 2020.
    13. Byrd, Deborah (26 February 2020). "New image of Earth's new mini-moon". EarthSky. Retrieved 26 February 2020.
    14. Crane, Leah (26 February 2020). "Earth has acquired a brand new moon that's about the size of a car". New Scientist. Retrieved 27 February 2020.
    15. "2020 CD3 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at discovery). Department of Mathematics, University of Pisa, Italy. Retrieved 28 February 2020.
    16. King, Bob (2 March 2020). "Earth Has A Mini-Moon — But Not for Long!". Sky & Telescope. Retrieved 3 March 2020.
    17. Howell, Elizabeth (28 February 2020). "How scientists found Earth's new minimoon and why it won't stay here forever". Space.com. Retrieved 29 February 2020.
    18. "How Are Minor Planets Named?". Minor Planet Center. International Astronomical Union. Retrieved 29 February 2020.
    19. Plait, Phil (27 February 2020). "The Earth has a new minimoon! But not for long..." Bad Astronomy. Syfy Wire. Retrieved 29 February 2020.
    20. Baoyin, He-Xi; Chen, Chen; Li, Jun-Feng (June 2010). "Capturing Near Earth Objects". Research in Astronomy and Astrophysics: Letters. 10 (6): 587–598. arXiv:1108.4767. Bibcode:2010RAA....10..587B. doi:10.1088/1674-4527/10/6/008.
    21. Naidu, Shantanu; Farnocchia, Davide. "Tiny Object Discovered in Distant Orbit Around the Earth". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 3 March 2020.
    22. Gough, Evan (27 February 2020). "Astronomers Discover a Tiny New Temporary Moon for the Earth. Welcome to the Family 2020 CD3". Universe Today. Retrieved 29 February 2020.
    23. Boyle, Rebecca (27 February 2020). "A New Mini-Moon Was Found Orbiting Earth. There Will Be More". The New York Times. Retrieved 29 February 2020.
    24. Tancredi, G. (September 1997). "An Asteroid in a Earth-like Orbit". Celestial Mechanics and Dynamical Astronomy. 69 (1/2): 119–132. Bibcode:1997CeMDA..69..119T. doi:10.1023/A:1008378316299.
    25. Gohd, Chelsea (2 December 2019). "Scientists Spot Rare Minimoon Fireball Over Australia". Space.com. Retrieved 29 February 2020.
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