2020 QG

2020 QG, also known by its internal designation ZTF0DxQ,[3] is an Earth-crossing asteroid, a few meters in diameter. It belongs to the Apollo group, and passed above the surface of Earth approximately 2,950 kilometres (1,830 mi) away[lower-alpha 2] (less than one-quarter of Earth's diameter) on 16 August 2020 at 04:09 UT.[4] It was first imaged by the Zwicky Transient Facility (ZTF) at the Palomar Observatory about 6 hours after this closest approach, and was later identified by Kunal Deshmukh, a student at the Indian Institute of Technology Bombay, along with colleagues Kritti Sharma, Chen-Yen Hsu and Bryce T. Bolin analyzing images from the ZTF.[5][2]

2020 QG
2020 QG imaged as a streak of light by the Zwicky Transient Facility on 16 August 2020
Discovery [1][2]
Discovered byZwicky Transient Facility
Discovery sitePalomar Obs.
Discovery date16 August 2020
Designations
2020 QG
ZTF0DxQ[3]
NEO · Apollo [1]
Orbital characteristics [4]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 6
Observation arc1.6 days[1][lower-alpha 1]
Aphelion2.8933±0.0009 AU
Perihelion0.99628 AU
1.9448±0.0006 AU
Eccentricity0.48772±0.0002
2.71 yr (990.51±0.47 d)
337.41±0.011°
0° 21m 48.696s / day
Inclination5.4727±0.004°
143.50°
1 August 2020 03:43 UT
162.01±0.003°
Earth MOID0.00027 AU (40,000 km)
Physical characteristics
Mean diameter
~3 m (est. at ~0.17)[3]
2–14 m (est. at 0.01–0.60)[3]
29.87±0.25[4]

    At the time, 2020 QG passed closer to Earth than any known asteroid, except for those that became meteors. It passed closer than 2011 CQ1 and 2020 JJ.[lower-alpha 3] Given an absolute magnitude of 29.8, it is estimated to be around 3–6 metres (10–20 ft) in diameter[3] so similar to Earth-impactors 2008 TC3, 2014 AA, 2018 LA, and 2019 MO.

    Orbit and classification

    2020 QG orbits the Sun at approximately 1.0–2.9 AU every 964.2 days (2.64 years) after its 2020 orbital perturbation by its close approach with Earth.[6] Before perturbation, it orbited every 990.5 days (with a semi-major axis of 1.9 AU).[4]

    Before its perturbation, flying by Earth, the asteroid's orbit had an eccentricity of 0.49 and an inclination of 5.5° (with respect to the ecliptic).[4] The asteroid came to perihelion (closest approach to the Sun) on 1 August, and then on 16 August 2020 the close approach to Earth reduced its orbital period. From the encounter with the larger gravity field, the orbital eccentricity became 0.48 and the inclination stands at 4.7°.[6]

    In May 2020, before any perturbation, the asteroid had an Earth-MOID (Minimum orbit intersection distance) of 0.00027 AU (40,000 km; 25,000 mi).[4] Hours before the close approach the Earth-MOID was 0.0001 AU (15,000 km; 9,300 mi),[2] the close-approach perturbation (change to orbit) bringing it closer.

    Orbital Elements[7]
    Parameter Epoch Period
    (p)    		 aphelion
    (Q)    		 perihelion
    (q)    		 Semi-major
    axis
    (a)    		 eccentricity
    (e)    		 inclination
    (i)
    Units (days) AU (°)
    Pre-flyby 2020-May-31[4] 990.6 2.893 0.9962 1.945 0.4877 5.473°
    Post-flyby 2020-Dec-01[6] 964.2 2.829 0.9908 1.910 0.4813 4.737°
    Animations of 2020 QG's orbit
    Asteroid 2020 QG trajectory
    (16 August 2020)
    Around the Sun
    Around the Earth
    View of flyby
      Sun ·    Earth ·    2020 QG

    Detectability

    Asteroids that are similar in size to 2020 QG are difficult to detect because they are small and therefore dim. Between 2010–2020, the asteroid was never brighter than about apparent magnitude 31[8] making it about 10 thousand times fainter than a typical discovery magnitude of 21.[lower-alpha 4] The Hubble Space Telescope needs 3 weeks of exposure time to image magnitude 31 objects and has an extremely small field of view, making serendipitous discoveries essentially impossible at those magnitudes. During the 2020 approach, the asteroid appeared dimmer than magnitude 24 until it had a solar elongation of only 60 degrees. The asteroid was imaged when it had a solar elongation of 125 degrees and was around magnitude 19.

    Future approaches

    2020 QG will make several close approaches with Earth in the future, albeit at larger distances compared to the August 2020 encounter. The next close approach by 2020 QG will be in May 2028, which it will pass by Earth from a nominal distance of 0.31 AU (120 LD).[4]

    See also
    Closest non-impacting asteroids to Earth, except Earth-grazing fireballs
    Asteroid Date Distance from
    surface of Earth    		 Uncertainty in
    approach distance    		 Reference
    2020 VT42020-11-13374 km±25 kmdata
    2020 QG2020-08-162946 km±20 kmdata
    2011 CQ12011-02-045481 km±5 kmdata
    2019 UN132019-10-316242 km±200 kmdata
    2008 TS262008-10-096259 km±1000 kmdata
    2004 FU1622004-03-316542 km±15000 kmdata

    Notes
    1. The Minor Planet Center's solution uses only 28 of the 35 observations.
    2. The asteroid passed about 9317±20 km from the center of Earth and Earth has a radius of 6371 km. (9317 – 6371 = 2946)
    3. Due to short arcs and the uncertainty in their approach distances asteroids such as 2004 FU162 and 2014 LY21 may have passed closer to Earth, but their nominal solutions did not.
    4. Asteroids are generally discovered when they are around apparent magnitude 19–21 because that is when they are bright enough to be detected by automated astronomical surveys. The Catalina Sky Survey and ATLAS have a limiting magnitude of 19.5. The Zwicky Transient Facility has a limiting magnitude of 20.5 and Pan-STARRS has a limiting magnitude of 24.

    References
    1. "2020 QG". Minor Planet Center. International Astronomical Union. Archived from the original on 24 August 2020. Retrieved 17 August 2020.
    2. Bolin, B.; Bhalerao, V.; Copperwheat, C.; Deshmukh, K.; Hsu, C.-Y.; Lin, Z.-Y.; Purdum, J.; Sharma, K.; et al. (17 August 2020). "MPEC 2020-Q51 : 2020 QG". Minor Planet Electronic Circular. Minor Planet Center. Archived from the original on 24 August 2020. Retrieved 17 August 2020.
    3. "2020 QG". NEO Exchange. Las Cumbres Observatory. 16 August 2020. Archived from the original on 24 August 2020. Retrieved 17 August 2020.
    4. "JPL Small-Body Database Browser: (2020 QG)" (2020-08-18 last obs.). Jet Propulsion Laboratory. Archived from the original on 19 August 2020. Retrieved 18 August 2020.
    5. Clavin, Whitney (18 August 2020). "ZTF Finds Closest Known Asteroid to Fly By Earth". Caltech. Archived from the original on 19 August 2020. Retrieved 18 August 2020.
    6. Horizons output. "Orbital Elements for Asteroid (2020 QG)" (based on JPL #3 with solution date: 2020-Aug-20). Archived from the original on 24 August 2020. Retrieved 24 August 2020. ("Ephemeris Type" select "Orbital Elements"  · "Center" should already be set for "Sun (body center)" (aka @sun)  · "Time Span" I selected "2020-May-31" to match the current JPL SBDB numbers and "2020-Dec-01" with a step size of 6 months.)
    7. "Ephemeris". Horizons.
    8. "2020QG Ephemerides for 2010–2020". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 24 August 2020. Retrieved 18 August 2020.

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