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][lower-alpha 1] 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 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

2021 UA1
Orbit of 2021 UA1
Discovery[1]
Discovered byCatalina Sky Survey
Discovery date25 October 2021
Designations
2021 UA1
Orbital characteristics[3]
Epoch 2021-Jul-01 (JD 2459396.5)
Uncertainty parameter 6
Observation arc0.9 days[2]
Aphelion1.35 AU (Q)
Perihelion0.6139 AU (q)
0.98 AU (a)
Eccentricity0.3750 (e)
0.97 years
312.8° (M)
Inclination10.19° (i)
211.6° (Ω)
66.27° (ω)
Earth MOID0.000064 AU (9,600 km)
Jupiter MOID3.7 AU (550,000,000 km)
Physical characteristics
Dimensions
  • ~2 m (7 ft)[2]
  • 1–3 meters
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] 355.61.3510.6140.9820.375010.19°
    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. "MPEC 2021-U95 : 2021 UA1". IAU Minor Planet Center. 26 October 2021. Retrieved 26 October 2021. (K21U01A)
    2. "Earth Impact Risk Summary: 2021 UA1". NASA/JPL Near-Earth Object Program Office. Retrieved 26 October 2021.
    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. "Horizons Batch for 2021-10-25 03:06 UT". JPL Horizons. Archived from the original on 26 October 2021. Retrieved 26 October 2021.
    6. "Horizons Batch showing epoch 2021-Jul-01 and 2022-Jan-01". JPL Horizons. Retrieved 26 October 2021.
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