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]

    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

    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.
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