1979 XB

1979 XB is a lost asteroid[2] with a short observation arc of 3.9 days that cannot be recovered with targeted observations and awaits serendipitous survey observations. It is classified as a near-Earth object and potentially hazardous asteroid of the Apollo group[3] and is estimated to be 660 meters (2,200 feet) in diameter.[4] The unnumbered minor planet has a poorly constrained orbit and has not been observed in 40 years. It has been listed on the Sentry Risk Table since the list started in 2002. With a cumulative Palermo Technical Impact Hazard Scale of −2.72, the poorly known orbit and assumed size place 1979 XB third on an unconstrained listing of the Sentry Risk Table.[5]

1979 XB
Discovery[1]
Discovered bySiding Spring Obs.
Discovery siteSiding Spring Obs.
Discovery date11 December 1979
(first observed only)
Designations
1979 XB
Lost[2] · Apollo · NEO · PHA[1][3] · risk listed[4]
Orbital characteristics[3]
Epoch 14 December 1979 (JD 2444221.5)
Uncertainty parameter 9
Observation arc3.9 days[4]
Aphelion3.8±0.7 AU (Q)
Perihelion0.65±0.01 AU (q)
2.2±0.4 AU (a)
Eccentricity0.7±0.06 (e)
3.3±0.9 years
346°±4° (M)
0° 17m 46.68s / day
Inclination24.7°±1.6° (i)
86°±0.12° (Ω)
75.6°±0.7° (ω)
Earth MOID0.02 AU (7.8 LD)?
Physical characteristics
Mean diameter
660 m (est.)[4]
500–1000 meters
18.6?[1][3]

    1979 XB was first observed on 11 December 1979 by astronomers at the Siding Spring Observatory, Australia, when the asteroid was estimated to be 0.09 ± 0.02 AU (13.5 ± 3.0 million km) from Earth and had a solar elongation of 127°. The object has never been confirmed by a second observatory.[1] The uncertainty region for this asteroid is now hundreds of millions of kilometers long.

    Orbit-fit

    With a short 4-day observation arc, the trajectory is poorly constrained and the uncertainties fit numerous different orbits. The perihelion point (closest approach to the Sun) is better known than the aphelion point (furthest distance from the Sun). Due to the uncertainty, the orbital period ranges from 2.4 to 4.2 years.[3]

    Epoch 2019 orbit fits for 1979 XB
    Source Aphelion Orbital period Earth MOID
    MPC[1]3.8 AU (570 million km)3.31 years (1,210 d)0.02 AU (3.0 million km)
    NEODyS[6]4.5 AU (670 million km)4.10 years (1,496 d)0.001 AU (150 thousand km)

    2024

    Around mid-December 2024 the asteroid has about a 0.05% chance of making an Earth approach within 0.1 AU.[7] But it will not pass any closer than 0.005 AU (750,000 km; 460,000 mi).[7] The nominal JPL Horizons December 2024 Earth distance is 4 AU (600,000,000 km; 370,000,000 mi) with an uncertainty of more than a billion km.[8]

    2056 virtual impactor

    JPL Horizons suggests that the closest approach the asteroid will make to Earth in 2056 is a distant 1.2 AU (180,000,000 km; 110,000,000 mi) on 4 August 2056.[8] NEODyS expects the closest Earth approach to be an even more distant 3.1 AU (460,000,000 km; 290,000,000 mi) on 2 October 2056.[9]

    With a short 4-day observation arc, the Sentry Risk Table shows an estimated 1 in 5 million chance of the asteroid impacting Earth on 12 December 2056.[4] The nominal JPL Horizons 12 December 2056 Earth distance is 3 AU (450,000,000 km; 280,000,000 mi) with a 3-sigma uncertainty of ±13 billion km.[10] NEODyS lists the nominal 12 December 2056 Earth distance as 3.6 AU (540,000,000 km; 330,000,000 mi).[9]

    Virtual impactors
    Date Impact
    probability
    (1 in)    		 JPL Horizons
    nominal geocentric
    distance (AU)    		 NEODyS
    nominal geocentric
    distance (AU)    		 uncertainty
    region
    2056-12-125 million3 AU (450 million km)[10]3.6 AU (540 million km)[9]±13 billion km[10]
    2113-12-142 million3.9 AU (580 million km)4.2 AU (630 million km)[11]±5 billion km

    See also

    References
    1. "1979 XB". Minor Planet Center. Retrieved 31 August 2019.
    2. "NEODyS-2 Risk List". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 20 November 2018. Retrieved 8 March 2021.
    3. "JPL Small-Body Database Browser: (1979 XB)" (1979-12-15 last obs.). Jet Propulsion Laboratory. Retrieved 31 August 2019. (Wayback Machine 2018-01-30)
    4. "Earth Impact Risk Summary: 1979 XB". NASA/JPL Near-Earth Object Program Office. Archived from the original on 19 August 2019. Retrieved 30 August 2019. (Wayback Machine 2002)
    5. "Sentry: Earth Impact Monitoring". NASA/JPL Center for NEO Studies. Retrieved 7 August 2021. (Use Unconstrained Settings to reveal 1979 XB with impact probability below 1e-7)
    6. "1979XB Orbital Information". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 31 August 2019. Retrieved 31 August 2019.
    7. "1979XB Close Approaches". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 30 August 2019. Retrieved 30 August 2019.
    8. Go to JPL Horizons. Table Settings: only need "20. Observer range & range-rate" AND "39. Range & range-rate 3-sigmas".
      RNG_3sigma = uncertainty range in km. (Soln.date: 2017-Apr-06 generates RNG_3sigma = 1.211291E9 for 2024-Dec-08)
    9. "1979XB Ephemerides for 2056". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 4 April 2021. Retrieved 4 April 2019.
    10. "Horizons Batch for 2056-12-12 Virtual Impactor". JPL Horizons. Retrieved 20 April 2021. RNG_3sigma = uncertainty range in km. (JPL#13/Soln.date: 2021-Apr-14 generates RNG_3sigma = 1.3E10 for 2056-Dec-12.)
    11. "1979XB Ephemerides for 2113-12-14". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 31 August 2019. Retrieved 31 August 2019.

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