2021 UA1

2021 UA₁ is a small (~2 meter) near-Earth object that passed about 3047 km from the surface of Earth while passing over Antarctica on 25 October 2021 around 03:07 UT.^[5][a] Given the small size of the asteroid it only reached the brightness of Pluto at around apparent magnitude 14.^[5] Since it approached from the direction of the Sun, it was not discovered until 4 hours after closest approach.^[1]

Closest non-impacting asteroids to Earth, except Earth-grazing fireballs
(using JPL SBDB numbers and Earth radius of 6,378 km)

Asteroid	Date	Distance from surface of Earth	Uncertainty in approach distance	Observation arc	Reference
2020 VT4	2020-11-13 17:21	368 km	±11 km	5 days (34 obs)	data
2020 QG	2020-08-16 04:09	2939 km	±11 km	2 days (35 obs)	data
2021 UA1	2021-10-25 03:07	3049 km	±10 km	1 day (22 obs)	data
2023 BU	2023-01-27 00:29	3589 km	±<1 km	10 days (231 obs)	data
2011 CQ1	2011-02-04 19:39	5474 km	±5 km	1 day (35 obs)	data
2019 UN13	2019-10-31 14:45	6235 km	±189 km	1 day (16 obs)	data
2008 TS26	2008-10-09 03:30	6260 km	±970 km	1 day (19 obs)	data
2004 FU162	2004-03-31 15:35	6535 km	±13000 km	1 day (4 obs)	data

2021 UA₁

Orbit of 2021 UA1
Discovery[1]
Discovered by	Catalina Sky Survey
Discovery date	25 October 2021
Designations
MPC designation	2021 UA1
Minor planet category	NEO Aten (pre-flyby) Apollo (post-flyby) risk listed[2]
Orbital characteristics[3]
Epoch 2021-Jul-01 (JD 2459396.5)
Uncertainty parameter 6
Observation arc	0.9 days[2]
Aphelion	1.35 AU (Q)
Perihelion	0.6139 AU (q)
Semi-major axis	0.98 AU (a)
Eccentricity	0.3750 (e)
Orbital period (sidereal)	0.97 years
Mean anomaly	312.8° (M)
Inclination	10.19° (i)
Longitude of ascending node	211.6° (Ω)
Argument of perihelion	66.27° (ω)
Earth MOID	0.000064 AU (9,600 km)
Jupiter MOID	3.7 AU (550,000,000 km)
Physical characteristics
Dimensions	~2 m (7 ft)[2] 1–3 meters
Absolute magnitude (H)	31.8[3][4]

The 2021 Earth approach lifted the orbit and increased the orbital period from 356 days to 413 days.^[6] This changed it from an Aten asteroid to an Apollo asteroid.

Orbital Elements

Parameter	Epoch	Period (p)	Aphelion (Q)	Perihelion (q)	Semi-major axis (a)	Eccentricity (e)	Inclination (i)
Units		(days)	AU				(°)
Pre-flyby	2021-Jul-01[3]	355.6	1.351	0.614	0.982	0.3750	10.19°
Post-flyby	2022-Jan-01[6]	413.1	1.525	0.646	1.086	0.4046	0.006°

Animation of 2021 UA1's orbit around Sun - 2021 Earth approach
  2021 UA1 ·   Mercury  ·   Venus  ·   Earth ·   Mars  ·   Sun

Notes

1. Geocentric approach distance 0.000063 AU – 6378 km (Earth radius) is 3047 km. It passed within 4 degrees of the South celestial pole near closest approach.