2021 SG

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
Mean diameter
42–94 m [5]
13.4 (discovery) [2]
24.01±0.24 [4][1]

    References
    1. "2021 SG". Minor Planet Center. International Astronomical Union. Retrieved 11 December 2021.
    2. "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. "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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