1979 XB

1979 XB
Discovery [1]
Discovered by	Siding Spring Obs.
Discovery site	Siding Spring Obs.
Discovery date	11 December 1979; (first observed only)
Designations
MPC designation	1979 XB
Minor planet category	Apollo · NEO · PHA [1][2] · risk listed
Orbital characteristics [2]
	Epoch 14 December 1979 (JD 2444221.5)
	Uncertainty parameter 9
Observation arc	3.9 days[3]
Aphelion	3.8±0.7 AU (Q)
Perihelion	0.65±0.01 AU (q)
Semi-major axis	2.2±0.4 AU (a)
Eccentricity	0.7±0.06 (e)
Orbital period	3.3±0.9 years
Mean anomaly	346°±4° (M)
Mean motion	0° 17m 46.68s / day
Inclination	24.7°±1.6° (i)
Longitude of ascending node	86°±0.12° (Ω)
Argument of perihelion	75.6°±0.7° (ω)
Earth MOID	0.02 AU (7.8 LD)?
Physical characteristics
Mean diameter	660 m (est.)[3]; 500–1000 meters
Absolute magnitude (H)	18.6?[1][2]

1979 XB is a lost asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group.[2] It has a short observation arc of 3.9 days and is roughly estimated to be 660 meters (2,200 feet) in diameter.[3] 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.

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 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.[2]

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[4]	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.[5] But it will not pass any closer than 0.005 AU (750,000 km; 460,000 mi).[5] 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.[6]

2056 virtual impactor

With a short 4 day observation arc, the Sentry Risk Table shows an estimated 1 in 6 million chance of the asteroid impacting Earth on 12 December 2056.[3] 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 ±14 billion km.[6] NEODyS lists the nominal 12 December 2056 Earth distance as 3.6 AU (540,000,000 km; 330,000,000 mi).

Virtual impactors
Date	Impact probability (1 in)	JPL Horizons nominal geocentric distance (AU)	NEODyS nominal geocentric distance (AU)	uncertainty region
2056-12-12	6 million	3 AU (450 million km)	3.6 AU (540 million km)	±14 billion km
2113-12-14	2 million	3.9 AU (580 million km)	4.2 AU (630 million km)[7]	±6 billion km

References

"1979 XB". Minor Planet Center. Retrieved 31 August 2019.
"JPL Small-Body Database Browser: (1979 XB)" (1979-12-15 last obs.). Jet Propulsion Laboratory. Retrieved 31 August 2019. (Wayback Machine 2018-01-30)
"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)
"1979XB Orbital Information". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 31 August 2019. Retrieved 31 August 2019.
"1979XB Close Approaches". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 30 August 2019. Retrieved 30 August 2019.
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)
"1979XB Ephemerides for 2113-12-14". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 31 August 2019. Retrieved 31 August 2019.

External links

Four asteroids on COLLISION course with Earth, 31 July 2019
1979 XB at NeoDyS-2, Near Earth Objects—Dynamic Site
- Ephemeris · Obs prediction · Orbital info · MOID · Proper elements · Obs info · Close · Physical info · NEOCC
1979 XB at ESA–space situational awareness
- Ephemerides · Observations · Orbit · Physical Properties · Summary
1979 XB at the JPL Small-Body Database
- Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

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[MPC-object-1] "1979 XB". Minor Planet Center. Retrieved 31 August 2019.

[jpldata-2] "JPL Small-Body Database Browser: (1979 XB)" (1979-12-15 last obs.). Jet Propulsion Laboratory. Retrieved 31 August 2019. (Wayback Machine 2018-01-30)

[sentry-3] "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)

[NEODyS-orbit-4] "1979XB Orbital Information". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 31 August 2019. Retrieved 31 August 2019.

[NEODyS-CA-5] "1979XB Close Approaches". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 30 August 2019. Retrieved 30 August 2019.

[Horizons-6] 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)

[NEODyS2113-7] "1979XB Ephemerides for 2113-12-14". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 31 August 2019. Retrieved 31 August 2019.