1979 XB

{{Short description|Lost near-Earth asteroid}} {{Use dmy dates|date=August 2019}} {{Infobox planet | minorplanet = yes | name = 1979 XB | background = #FFC2E0 | image = | image_size = | caption = | discovery_ref = <ref name="MPC-object" /> | discoverer = Siding Spring Obs. | discovery_site = Siding Spring Obs. | discovered = 11 December 1979 {{small|(first observed only)}} | mpc_name = 1979 XB | alt_names = | mp_category = {{nowrap|Lost<ref name="lost"/>{{·}}Apollo{{·}}NEO{{·}}PHA<ref name="MPC-object" /><ref name="jpldata"/>}}{{·}}risk listed<ref name=sentry/> | orbit_ref = <ref name="jpldata" /> | epoch = 14 December 1979 (JD 2444221.5) | uncertainty = 9 | observation_arc = 3.9 days<ref name=sentry/> | aphelion = {{val|3.8|0.7|ul=AU}} (Q) | perihelion = {{val|0.65|0.01|u=AU}} (q) | semimajor = {{val|2.2|0.4|u=AU}} (a) | eccentricity = {{val|0.7|0.06}} (e) | period = {{val|3.3|0.9|u=years}} | mean_anomaly = {{val|346|4|ul=°}} (M) | mean_motion = {{Deg2DMS|0.2963|sup=ms}} / day | inclination = {{val|24.7|1.6|u=°}} (i) | asc_node = {{val|86|0.12|u=°}} (Ω) | arg_peri = {{val|75.6|0.7|u=°}} (ω) | moid = {{convert|0.02|AU|LD|abbr=on}}? | mean_diameter = {{val|660|ul=m}} {{small|(est.)}}<ref name=sentry/> 500–1000 meters | rotation = | albedo = | spectral_type = | abs_magnitude = 18.6?<ref name="MPC-object" /><ref name="jpldata" /> }}

'''1979 XB''' is a lost asteroid<ref name="lost"/> 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<ref name="jpldata" /> and is estimated to be {{convert|660|m|ft|abbr=off|sp=us|sigfig=2}} in diameter.<ref name=sentry/> The unnumbered minor planet has a poorly constrained orbit and has not been observed in {{age|1979|12|11}} years. It has been listed on the Sentry Risk Table since the list started in 2002. {{As of|2025|2|11}}, With a cumulative Palermo scale rating of −2.70, the poorly known orbit and assumed size place 1979 XB fourth on an unconstrained listing of the Sentry Risk Table.<ref name="risk-table"/>

1979 XB was first observed on 11 December 1979 by astronomers at the Siding Spring Observatory, Australia, when the asteroid was estimated to be {{convert|0.09|+/-|0.02|AU|e6km|abbr=unit|lk=in}} from Earth and had a solar elongation of 127°. The object has never been confirmed by a second observatory.<ref name="MPC-object" /> 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.<ref name="jpldata"/>

{| class="wikitable sortable" style="font-size: 0.9em;" |+Epoch 2019 orbit fits for 1979 XB ! Source ! Aphelion ! Orbital period ! Earth MOID |- |MPC<ref name="MPC-object"/> || {{Convert|3.8|AU|e6km|abbr=unit}} || {{Convert|3.31|years|days}} || {{Convert|0.02|AU|e6km|abbr=unit}} |- |NEODyS<ref name="NEODyS-orbit"/> || {{Convert|4.5|AU|e6km|abbr=unit}} || {{Convert|1496|days|years|order=flip}} || {{Convert|0.001|AU|e3km|abbr=unit}} |}

== 2024 == Around mid-December 2024 the asteroid had about a 0.05% chance of making an Earth approach within 0.1 AU.<ref name="NEODyS-CA"/> If it did make an Earth approach, it did not come any closer than {{convert|0.005|AU|km mi|abbr=on}}.<ref name="NEODyS-CA"/> The nominal JPL Horizons December 2024 Earth distance is {{convert|4|AU|km mi|abbr=on}} with an uncertainty of more than a billion km.<ref name=Horizons/>

== 2056 virtual impactor == JPL Horizons suggests that the closest approach the asteroid will make to Earth in 2056 is a distant {{convert|1.2|AU|km mi|abbr=on}} on 4 August 2056.<ref name=Horizons/> NEODyS expects the closest Earth approach to be an even more distant {{convert|3.1|AU|km mi|abbr=on}} on 2 October 2056.<ref name="NEODyS2056"/>

With a short 4-day observation arc, {{As of|2025|2|lc=y}}, the Sentry Risk Table shows an estimated 1 in 5.3 million chance of the asteroid impacting Earth on 12 December 2056.<ref name=sentry/> The nominal JPL Horizons 12 December 2056 Earth distance is {{convert|3|AU|km mi|abbr=on}} with a 3-sigma uncertainty of ±13 billion km.<ref name="Horizons2056"/> NEODyS lists the nominal 12 December 2056 Earth distance as {{convert|3.6|AU|km mi|abbr=on}}.<ref name="NEODyS2056"/>

The Sentry Risk Table also lists potential impacts in 2086, 2102 and 2113.<ref name=sentry/>

{| class="wikitable sortable" style="font-size: 0.9em;" |+Virtual impactors ! Date ! Sentry impact probability<ref name=sentry/> (1 in) ! JPL Horizons nominal geocentric distance & uncertainty region (AU) ! NEODyS nominal geocentric distance (AU) |- |2056-12-12 || 5.3 million ||{{Convert|3.0|AU|e6km|abbr=unit}} ±{{Convert|89.6|AU|e6km|abbr=unit}}<ref name="Horizons2056"/> ||{{Convert|3.2|AU|e6km|abbr=unit}}<ref name="NEODyS2056"/> |- |2086-12-16 || 9.1 million ||{{Convert|3.3|AU|e6km|abbr=unit}} ±{{Convert|64.9|AU|e6km|abbr=unit}}<ref name="Horizons2086"/> ||{{Convert|3.3|AU|e6km|abbr=unit}}<ref name="NEODyS2086"/> |- |2102-12-16 || 8.3 billion ||{{Convert|0.4|AU|e6km|abbr=unit}} ±{{Convert|76.8|AU|e6km|abbr=unit}}<ref name="Horizons2102"/> ||{{Convert|0.6|AU|e6km|abbr=unit}}<ref name="NEODyS2102"/> |- |2113-12-14 || 1.8 million ||{{Convert|3.9|AU|e6km|abbr=unit}} ±{{Convert|32.0|AU|e6km|abbr=unit}}<ref name="Horizons2113"/> ||{{Convert|3.9|AU|e6km|abbr=unit}}<ref name="NEODyS2113"/> |}

== See also == * {{mpl|2007 FT|3}} * {{Section link|List of unnumbered minor planets|1970–1979}}

== References == {{Reflist|refs=

<ref name="jpldata">{{cite web |type = 1979-12-15 last obs. |title = JPL Small-Body Database Browser: (1979 XB) |url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3012393 |publisher = Jet Propulsion Laboratory |accessdate = 31 August 2019}} [https://web.archive.org/web/20180130130300/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1979XB;cad=1 (Wayback Machine 2018-01-30)]</ref>

<ref name="MPC-object">{{cite web |title = 1979 XB |work = Minor Planet Center |url = https://www.minorplanetcenter.net/db_search/show_object?object_id=1979+XB |accessdate = 31 August 2019}}</ref>

<ref name="risk-table">{{cite web |title= Sentry: Earth Impact Monitoring |publisher=NASA/JPL Center for NEO Studies |url=https://cneos.jpl.nasa.gov/sentry/ |access-date=2025-02-11}} (Use Unconstrained Settings to reveal 1979 XB with impact probability below 1e-7)</ref>

<ref name=sentry>{{cite web |title=Earth Impact Risk Summary: 1979 XB |publisher=NASA/JPL CNEOS |url=https://cneos.jpl.nasa.gov/sentry/details.html#?des=1979%20XB |accessdate=2025-02-11 |url-status=live |archive-url=https://web.archive.org/web/20250210173009/https://cneos.jpl.nasa.gov/sentry/details.html#?des=1979%20XB |archive-date=2025-02-10}}</ref>

<ref name="NEODyS-CA">{{cite web |title=1979XB Close Approaches |publisher=NEODyS (Near Earth Objects – Dynamic Site) |url=https://newton.spacedys.com//neodys/index.php?pc=1.1.8&n=1979XB |archive-url=https://archive.today/20190830150644/https://newton.spacedys.com//neodys/index.php?pc=1.1.8&n=1979XB |archive-date=30 August 2019 |url-status=live |accessdate=2019-08-30 }}</ref>

<ref name="NEODyS-orbit">{{cite web |title=1979XB Orbital Information |publisher=NEODyS (Near Earth Objects – Dynamic Site) |url=https://newton.spacedys.com//neodys/index.php?pc=1.1.1&n=1979XB |archive-url=https://web.archive.org/web/20190831213944/https://newton.spacedys.com//neodys/index.php?pc=1.1.1&n=1979XB |archive-date=2019-08-31 |url-status=live |accessdate=2019-08-31 }}</ref>

<ref name="lost">{{cite web |title=NEODyS-2 Risk List |publisher=NEODyS (Near Earth Objects – Dynamic Site) |url=https://newton.spacedys.com/neodys/index.php?pc=4.1 |archive-url=https://web.archive.org/web/20181120220955/https://newton.spacedys.com/neodys/index.php?pc=4.1 |archive-date=2018-11-20 |url-status=live |accessdate=2021-03-08 }}</ref>

<ref name=Horizons>Go to [https://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=1979XB 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)</ref>

<ref name="Horizons2056">{{cite web |title=Horizons Batch for 2056-12-12 Virtual Impactor |publisher=JPL Horizons |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%271979+XB%27&START_TIME=%272056-12-12%27&STOP_TIME=%272056-12-13%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27 |accessdate=2025-02-11}}</ref>

<ref name="Horizons2086">{{cite web |title=Horizons Batch for 2086-12-16 Virtual Impactor |publisher=JPL Horizons |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%271979+XB%27&START_TIME=%272086-12-16%27&STOP_TIME=%272086-12-17%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27 |accessdate=2025-02-11}}</ref>

<ref name="Horizons2102">{{cite web |title=Horizons Batch for 2102-12-16 Virtual Impactor |publisher=JPL Horizons |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%271979+XB%27&START_TIME=%272102-12-16%27&STOP_TIME=%272102-12-17%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27 |accessdate=2025-02-11}}</ref>

<ref name="Horizons2113">{{cite web |title=Horizons Batch for 2113-12-14 Virtual Impactor |publisher=JPL Horizons |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%271979+XB%27&START_TIME=%272113-12-14%27&STOP_TIME=%272113-12-15%27&STEP_SIZE=%272%20days%27&QUANTITIES=%2720,39%27 |accessdate=2025-02-11}}</ref>

<ref name="NEODyS2056">{{cite web |title=1979XB Ephemerides for 2056 |publisher=NEODyS (Near Earth Objects – Dynamic Site) |url=https://newton.spacedys.com/neodys/index.php?pc=1.1.3.1&n=1979XB&oc=500&y0=2056&m0=1&d0=1&h0=0&mi0=0&y1=2056&m1=12&d1=31&h1=0&mi1=0&ti=1.0&tiu=days |accessdate=2025-02-11}}</ref>

<ref name="NEODyS2086">{{cite web |title=1979XB Ephemerides for 2086 |publisher=NEODyS (Near Earth Objects – Dynamic Site) |url=https://newton.spacedys.com/neodys/index.php?pc=1.1.3.1&n=1979XB&oc=500&y0=2086&m0=1&d0=1&h0=0&mi0=0&y1=2086&m1=12&d1=31&h1=0&mi1=0&ti=1.0&tiu=days |accessdate=2025-02-11}}</ref>

<ref name="NEODyS2102">{{cite web |title=1979XB Ephemerides for 2102 |publisher=NEODyS (Near Earth Objects – Dynamic Site) |url=https://newton.spacedys.com/neodys/index.php?pc=1.1.3.1&n=1979XB&oc=500&y0=2102&m0=1&d0=1&h0=0&mi0=0&y1=2102&m1=12&d1=31&h1=0&mi1=0&ti=1.0&tiu=days |accessdate=2025-02-11}}</ref>

<ref name="NEODyS2113">{{cite web |title=1979XB Ephemerides for 2113-12-14 |publisher=NEODyS (Near Earth Objects – Dynamic Site) |url=https://newton.spacedys.com/neodys/index.php?pc=1.1.3.1&n=1979XB&oc=500&y0=2113&m0=12&d0=13&h0=0&mi0=0&y1=2113&m1=12&d1=15&h1=0&mi1=0&ti=1.0&tiu=days |accessdate=2025-02-11}}</ref>

}}

== External links == * {{NeoDys|1979+XB}} * {{ESA-SSA|1979XB}} * {{JPL small body|id=3012393}}

{{Small Solar System bodies}} {{Authority control}}

{{DEFAULTSORT:1979 XB}} # Category:Minor planet object articles (unnumbered) # Category:Lost minor planets # Category:Potential impact events caused by near-Earth objects 19791211