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 by	Zwicky Transient Facility
Discovery site	Palomar Obs.
Discovery date	17 September 2020
Designations
MPC designation	2021 SG
Alternative designations	ZTF0MtF [3]
Minor planet category	NEO · Apollo [4]
Orbital characteristics [4]
Epoch 21 January 2022 (JD 2459600.5)
Uncertainty parameter 7
Observation arc	7 days
Aphelion	2.953 AU
Perihelion	0.4730 AU
Semi-major axis	1.713 AU
Eccentricity	0.7238
Orbital period (sidereal)	2.24 yr (818.77 days)
Mean anomaly	76.606°
Mean motion	0° 26m 22.869s / day
Inclination	3.176°
Longitude of ascending node	352.203°
Argument of perihelion	256.579°
Earth MOID	0.00157 AU (235,000 km)
Physical characteristics
Mean diameter	42–94 m [5]
Apparent magnitude	13.4 (discovery) [2]
Absolute magnitude (H)	24.01±0.24 [4][1]

References

External links

Wikimedia Commons has media related to 2021 SG.

• 2021 SG at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

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