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]
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]
^"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)
^ abGo 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)