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
2025 UC112025-10-30 12:11237 km±11 km1 day (41 obs)data
2020 VT42020-11-13 17:21368 km±11 km5 days (34 obs)data
2020 QG2020-08-16 04:092939 km±11 km2 days (35 obs)data
2021 UA12021-10-25 03:073049 km±10 km1 day (22 obs)data
2023 BU2023-01-27 00:293589 km±<1 km10 days (231 obs)data
2011 CQ12011-02-04 19:395474 km±5 km1 day (35 obs)data
2019 UN132019-10-31 14:456235 km±189 km1 day (16 obs)data
2008 TS262008-10-09 03:306260 km±970 km1 day (19 obs)data
2004 FU1622004-03-31 15:356535 km±13000 km1 day (4 obs)data

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] 355.61.3510.6140.9820.375010.19°
Post-flyby 2022-Jan-01[6] 413.11.5250.6461.0860.40460.006°
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.

References

  1. 1 2 "MPEC 2021-U95 : 2021 UA1". IAU Minor Planet Center. 26 October 2021. Retrieved 26 October 2021. (K21U01A)
  2. 1 2 3 "Earth Impact Risk Summary: 2021 UA1". NASA/JPL Near-Earth Object Program Office. Retrieved 26 October 2021.
  3. 1 2 3 "JPL Small-Body Database Browser: (2021 UA1)" (Under Close Approach Data select km for distance units). Jet Propulsion Laboratory. Retrieved 26 October 2021.
  4. ↑ "2021 UA1 Orbit". Minor Planet Center. Retrieved 26 October 2021.
  5. 1 2 "Horizons Batch for 2021-10-25 03:06 UT". JPL Horizons. Archived from the original on 26 October 2021. Retrieved 26 October 2021.
  6. 1 2 "Horizons Batch showing epoch 2021-Jul-01 and 2022-Jan-01". JPL Horizons. Retrieved 26 October 2021.
source: https://en.wikipedia.org/wiki/2021_UA1