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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 44 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]
| Discovery[1] | |
|---|---|
| Discovered by | Siding Spring Obs. |
| Discovery site | Siding Spring Obs. |
| Discovery date | 11 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 arc | 3.9 days[4] |
| Aphelion | 3.8±0.7 AU (Q) |
| Perihelion | 0.65±0.01 AU (q) |
| 2.2±0.4 AU (a) | |
| Eccentricity | 0.7±0.06 (e) |
| 3.3±0.9 years | |
| 346°±4° (M) | |
| 0° 17m 46.68s / day | |
| Inclination | 24.7°±1.6° (i) |
| 86°±0.12° (Ω) | |
| 75.6°±0.7° (ω) | |
| Earth MOID | 0.02 AU (7.8 LD)? |
| Physical characteristics | |
| 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.
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]
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]
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]
| Date | Impact probability (1 in) |
JPL Horizons nominal geocentric distance (AU) |
NEODyS nominal geocentric distance (AU) |
uncertainty region |
|---|---|---|---|---|
| 2056-12-12 | 5 million | 3 AU (450 million km)[10] | 3.6 AU (540 million km)[9] | ±13 billion km[10] |
| 2113-12-14 | 2 million | 3.9 AU (580 million km) | 4.2 AU (630 million km)[11] | ±5 billion km |
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