# 2020 CD3

Discovery [1][2] 2020 CD3 imaged in color by Gemini North Mt. Lemmon Survey Mt. Lemmon Obs. (CSS) 15 February 2020 2020 CD3 C26FED2 [3][4] temporarily captured [1] · co-orbital [5] Epoch 1 July 2021 (JD 2459396.5) Uncertainty parameter 0 2.03 yr (742 days) 9 May 2018 1.0416 AU 1.0160 AU 1.0288 AU 0.01246 1.04 yr (381.13 d) 129.525° 0° 56m 40.373s / day 0.6342° 82.210° 50.016° 0.02102 AU 0.9±0.1 m (albedo of 0.35)[7]1.2±0.1 m (albedo of 0.23)[7] ~4,900 kg (est.)[8] 2.1±0.7 g/cm3[7] 1,146.8 s or19.114 min (double-peaked solution)573.4 s (single-peaked solution)[7] 0.35 (assumed V-type)[7]0.23 (assumed from main belt) V[7]B–V=0.90±0.07[7]V–R=0.46±0.08R–I=0.44±0.06 >30 (current)[9]20 (at discovery)[2] 31.80±0.34[6]31.8[2] .mw-parser-output .reflist{font-size:90%;margin-bottom:0.5em;list-style-type:decimal}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}

2020 CD3 (also 2020CD3 or CD3 for short)[10][11] is a tiny near-Earth asteroid (or minimoon) that ordinarily orbits the Sun but makes close approaches to the Earth–Moon system, in which it can temporarily enter Earth orbit through temporary satellite capture (TSC). 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 was orbiting 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 around 2016–2017, and escaped Earth's gravitational sphere of influence around 7 May 2020.[5][7][12] 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.[13][14]

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).[15][16] 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[17]

2020 CD3 was discovered on 15 February 2020, by astronomers Theodore Pruyne and Kacper Wierzchoś 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][17] 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.[18][19][a] 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 an artificial object, such as a dead satellite or rocket booster, had not yet been fully ruled out.[20][19]

Precovery images of 2020 CD3 have been identified back to May 2018.[2]

## 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 modest observation arc of a couple years and that it has not been observed at enough oppositions.[21]

## 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.[b]

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 2016–2017, and left geocentric orbit by May 2020 according to simulations of its orbit.[5][7] 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.[22][20] 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 leads to ejection from its geocentric orbit as the Moon's perturbations can transfer enough momentum for 2020 CD3 to escape Earth's gravitational influence.[23][22][24]

2020 CD3's orbit around Earth is highly variable and eccentric, hence predictions of its past trajectory before mid-2017 are uncertain.[16][24] Due to the Yarkovsky effect on small asteroids, the first precovery image being from 2018, and numerous approaches to the Earth and Moon, it is unknown if the asteroid was closer than the Moon on Christmas Day 2015.[25]

Earth Approach Christmas Day 2015?[25]
Date JPL Horizons
nominal geocentric
distance (AU)
NEODyS
nominal geocentric
distance (AU)
Find_Orb
nominal geocentric
distance (AU)
ESA NEOCC
nominal geocentric
distance (AU)
MPC
nominal geocentric
distance (AU)
2015-Dec-25 0.0006 AU (90 thousand km) 0.0162 AU (2.42 million km) 0.288 AU (43.1 million km) 0.345 AU (51.6 million km) 0.834 AU (124.8 million km)

Between September 2017 and February 2020 it made 12 close approaches to Earth,[13] during which time it was never more than 0.0112 AU (1.68 million km) from Earth.[26] According to the JPL Small-Body Database, on 15 September 2017 it passed 12,000 km (7,500 mi) from the Moon.[6] The closest approach to Earth occurred on 4 April 2019, when it approached to a distance of 13,104 km (8,142 mi).[6][c] The final close approach in 2020 occurred on 13 February 2020 at a distance of about 41,000 km (25,000 mi) from Earth's surface.[24] The orbital period of 2020 CD3 around Earth ranged from 70 to 90 days.[24] 2020 CD3 escaped Earth's hill sphere at roughly 0.01 AU (1.5 million km) in March 2020[24][27] and returned to solar orbit on 7 May 2020.[5]

Escaping Geocentric Orbit 7 May 2020[d]
(assuming the Earth+Asteroid are the only objects in the Solar System)
Epoch Earth distance[27] Geocentric
eccentricity[12]
Apogee[12] Orbital period[12]
2020-May-07 0.0189 AU (2.83 million km) 0.9901 2.25 AU (337 million km) 693.61 years (253,341 d)
2020-May-08 0.0191 AU (2.86 million km) 1.0347 ${\displaystyle \infty }$ ${\displaystyle \infty }$

Being captured into a temporary orbit around Earth, 2020 CD3 is a temporarily captured object or a temporary satellite of Earth.[1][28] 2020 CD3 has also been widely referred to in the media as a "mini-moon" of Earth, due to its small size.[17][15][16][29] 2020 CD3 is the second known temporary captured object discovered in situ around Earth, with the first being 2006 RH120 discovered in 2006.[29] Other objects have also been suspected to have once been temporarily captured, including the small near-Earth asteroid 1991 VG and the bolide DN160822 03.[30][31] 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.[29]

### Future approaches

2020 CD3 will continue orbiting the Sun and will approach Earth on 20 March 2044, from a distance of 0.0245 AU (3.67 million km; 2.28 million mi).[13] 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[14] and outside of Earth's hill sphere. The next encounter will be August 2061, when it is expected to approach Earth from a nominal distance of 0.034 AU (5.1 million km; 3.2 million mi).[13] After the 2061 encounter the uncertainties in future encounters become much greater. By 2082 close approaches have a 3-sigma uncertainty of ±7 days.[6]

The possibility of 2020 CD3 impacting Earth has been considered by the Jet Propulsion Laboratory's Sentry risk table.[8] JPL's solution accounts for non-gravitational forces[6] as the multi-decade motion of a very small object is greatly affected by solar heating. Being only a few meters in size, an impact by 2020 CD3 would pose no threat to Earth as it would most likely fragment and disintegrate upon atmospheric entry.[19] With a cumulative impact probability of 2.5%,[8] it is listed as the second most likely object to impact Earth, but because of the harmless size of 2020 CD3, it is given a Torino Scale rating of 0 and a cumulative Palermo Scale rating of –5.20[8] Within the next 100 years, the date with the highest probability of impact is 9 September 2082, which is estimated to have an impact probability of 0.85% and a negligible Palermo Scale rating of –5.66.[8] JPL Horizon's nominal orbit has the asteroid passing 0.00251 AU (375 thousand km) from Earth on 8 October 2082 (29 days after the virtual impactor).[32]

## Physical characteristics

2020 CD3 is estimated to have an absolute magnitude (H) around 31.7, indicating that it is very small in size.[6] Studies reported in November 2020 have determined that the asteroid is about 1–2 m (3.3–6.6 ft) in diameter.[10][11] The rotation period and albedo of 2020 CD3 have not been measured due to the limited number of observations.[20] 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.[16][28] 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]

## 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. ^ 13104 km – Earth radius of 6371 km is 6733 km from the surface of Earth.
4. ^ Already outside of the Earth's Hill sphere which has a radius of roughly 0.01 AU (1.5 million km).

## 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. ^ a b c d "2020 CD3". Minor Planet Center. International Astronomical Union. Retrieved 25 February 2020.
3. ^ a b "2020 CD3". NEO Exchange. Las Cumbres Observatory. 15 February 2020. Retrieved 25 February 2020.
4. ^ a b c d ""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. S2CID 214605877.
6. "JPL Small-Body Database Browser: 2020 CD3" (2020-03-22 last obs.). Jet Propulsion Laboratory. Retrieved 25 February 2020.
7. Bolin, Bryce T.; Fremling, Christoffer; Holt, Timothy R.; Hankins, Matthew J.; Ahumada, Tomás; Anand, Shreya; et al. (August 2020). "Characterization of Temporarily-Captured Minimoon 2020 CD3 by Keck Time-resolved Spectrophotometry". The Astrophysical Journal. 900 (2): L45. arXiv:2008.05384. Bibcode:2020ApJ...900L..45B. doi:10.3847/2041-8213/abae69. S2CID 221103592.
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. ^ a b Crewe, Ralph (24 November 2020). "Here's what we know about Earth's new minimoon". Universe Today. Retrieved 25 November 2020.
11. ^ a b Fedorets, Grigori; et al. (23 November 2020). "Establishing Earth's Minimoon Population through Characterization of Asteroid 2020 CD3". The Astronomical Journal. 160 (6): 277. arXiv:2011.10380. Bibcode:2020AJ....160..277F. doi:10.3847/1538-3881/abc3bc. S2CID 227119071. Retrieved 25 November 2020.
12. ^ a b c d "JPL Horizons On-Line Ephemeris for 2020 CD3 orbit of Earth (geocentric) at epoch 2020-May-07". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Archived from the original on 8 June 2022. Retrieved 8 July 2022. Geocentric solution. Ephemeris Type: Orbital Elements / Center: @399
13. ^ a b c d "2020CD3 Close Approaches". Near Earth Objects – Dynamic Site. Department of Mathematics, University of Pisa, Italy. Archived from the original on 23 October 2021. Retrieved 1 March 2020.
14. ^ a b Koren, Marina (20 March 2020). "A Fleeting Moment in the Solar System". The Atlantic. Retrieved 2 April 2020.
15. ^ a b Byrd, Deborah (26 February 2020). "New image of Earth's new mini-moon". EarthSky. Retrieved 26 February 2020.
16. ^ a b c d 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.
17. ^ a b c "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.
18. ^ "2020 CD3 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at discovery). Department of Mathematics, University of Pisa, Italy. Retrieved 28 February 2020.
19. ^ a b c King, Bob (2 March 2020). "Earth Has A Mini-Moon — But Not for Long!". Sky & Telescope. Retrieved 3 March 2020.
20. ^ a b c 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.
21. ^ "How Are Minor Planets Named?". Minor Planet Center. International Astronomical Union. Retrieved 29 February 2020.
22. ^ a b Plait, Phil (27 February 2020). "The Earth has a new minimoon! But not for long..." Bad Astronomy. Syfy Wire. Retrieved 29 February 2020.
23. ^ Baoyin, He-Xi; Chen, Chen; Li, Jun-Feng (June 2010). "Capturing Near Earth Objects". Research in Astronomy and Astrophysics. 10 (6): 587–598. arXiv:1108.4767. Bibcode:2010RAA....10..587B. doi:10.1088/1674-4527/10/6/008. S2CID 119251954.
24. 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.
25. ^ a b "Horizons Batch for Christmas 2015 Geocentric distance" (Nominal is 0.0006 AU (90,000km)). JPL Horizons. Archived from the original on 13 July 2022. Retrieved 13 July 2022. (JPL#27/Soln.date: 2021-Jun-25) (NEODyS-2 on 25 Dec 2015) (Find_Orb on 25 Dec 2015) (ESA NEOCC on 25 Dec 2015)
26. ^ "Horizons Batch for September 2017 – April 2020 Geocentric distance" (Maximum Apogee occurs 2020-Jan-05 @ 0.011179 (1.7 million km)). JPL Horizons. Archived from the original on 11 July 2022. Retrieved 11 July 2022. (JPL#27/Soln.date: 2021-Jun-25) (NEODyS-2 for 5 Jan 2020)
27. ^ a b "Horizons Batch for March 2020 – May 2020 Geocentric distance" (Escaping Earth's Hill Sphere @ ~0.01au). JPL Horizons. Archived from the original on 8 June 2022. Retrieved 7 July 2022. (JPL#27/Soln.date: 2021-Jun-25)
28. ^ a b 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.
29. ^ a b c 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.
30. ^ 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. S2CID 189823446.
31. ^ Gohd, Chelsea (2 December 2019). "Scientists Spot Rare Minimoon Fireball Over Australia". Space.com. Retrieved 29 February 2020.
32. ^ "Horizons Batch for September 2082 – November 2082 Geocentric distance" (Earth approach occurs 2082-Oct-08 06:47 @ 0.002507 AU). JPL Horizons. Retrieved 10 July 2022. (JPL#27/Soln.date: 2021-Jun-25)