2021 SG is a near-Earth asteroid, with an estimated diameter of 42 to 94 meters, that passed about half a lunar distance from Earth on 16 September 2021. It approached from the direction of the Sun, so it was invisible until a day later.[6] It completes its highly eccentric orbit in 2.24 years. 2021 SG is an Apollo asteroid with a 1.71 AU semimajor axis, and a 0.473 AU perihelion (near Mercury at perihelion) out to a 2.95 AU aphelion (between Mars and Jupiter). With an absolute magnitude (H) of 24.0, it is possibly the largest asteroid to pass within 1 lunar distance of Earth during 2021.[2]

2021 SG
Orbit of 2021 SG
Discovery [1][2]
Discovered byZwicky Transient Facility
Discovery sitePalomar Obs.
Discovery date17 September 2020
Designations
2021 SG
ZTF0MtF [3]
NEO · Apollo[4]
Orbital characteristics[4]
Epoch 21 January 2022 (JD 2459600.5)
Uncertainty parameter 7
Observation arc7 days
Aphelion2.953 AU
Perihelion0.4730 AU
1.713 AU
Eccentricity0.7238
2.24 yr (818.77 days)
76.606°
0° 26m 22.869s / day
Inclination3.176°
352.203°
256.579°
Earth MOID0.00157 AU (235,000 km)
Physical characteristics
42–94 m [5]
13.4 (discovery) [2]
24.01±0.24[4][1]

References

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  1. ^ a b "2021 SG". Minor Planet Center. International Astronomical Union. Retrieved 11 December 2021.
  2. ^ a b c "MPEC 2021-S24 : 2021 SG". Minor Planet Electronic Circular. Minor Planet Center. 17 September 2021. Retrieved 11 December 2021.
  3. ^ "2021 SG". NEO Exchange. Las Cumbres Observatory. 17 September 2021. Retrieved 11 December 2021.
  4. ^ a b c "JPL Small-Body Database Browser: (2021 SG)" (2021-09-24 last obs.). Jet Propulsion Laboratory. Retrieved 11 December 2021.
  5. ^ "NEO Earth Close Approaches". Center for Near Earth Asteroid Studies. Jet Propulsion Laboratory. Retrieved 11 December 2021.
  6. ^ "EarthSky | Asteroid 2021 SG came from the sun's direction". 20 September 2021.
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