minimum orbit intersection distance

{{short description|Measure of close approach or collision risk in astronomy}}

{{Use dmy dates|date=March 2015}}

File:4953 DYK.svg, which, with a MOID of 0.0263 AU, is classified as a potentially hazardous object]]

Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects.[https://solarsystem.nasa.gov/basics/chapter1-3 Basics of Space Flight: The Solar System, p. 3], NASA Science, retrieved 14 May 2009 (from JPL site), [https://web.archive.org/web/20210917185720/https://solarsystem.nasa.gov/basics/chapter1-3/ archived] 17 September 2021. It is defined as the distance between the closest points of the osculating orbits of two bodies. Of greatest interest is the risk of a collision with Earth. Earth MOID is often listed on comet and asteroid databases such as the JPL Small-Body Database. MOID values are also defined with respect to other bodies as well: Jupiter MOID, Venus MOID and so on.

An object is classified as a potentially hazardous object (PHO) – that is, posing a possible risk to Earth – if, among other conditions, its Earth MOID is less than 0.05 AU. For more massive bodies than Earth, there is a potentially notable close approach with a larger MOID; for instance, Jupiter MOIDs less than 1 AU are considered noteworthy since Jupiter is the most massive planet.Bruce Koehn, "[http://www.lowell.edu/users/elgb/moid.html Minimum Orbital Intersection Distance]", Lowell Observatory, retrieved online 14 May 2009, [https://web.archive.org/web/20150715151635/https://lowell.edu/users/elgb/moid.html archived] 15 July 2015.

A low MOID does not mean that a collision is inevitable as the planets frequently perturb the orbit of small bodies. It is also necessary that the two bodies reach that point in their orbits at the same time before the smaller body is perturbed into a different orbit with a different MOID value. Two objects gravitationally locked in orbital resonance may never approach one another. Numerical integrations become increasingly divergent as trajectories are projected further forward in time, especially beyond times where the smaller body is repeatedly perturbed by other planets. MOID has the convenience that it is obtained directly from the orbital elements of the body and no numerical integration into the future is used.Brian G. Marsden, [http://www.cfa.harvard.edu/iau/pressinfo/100PHAs.html "Press Information Sheet:Potentially Hazardous Asteroids"], Harvard-Smithsonian Center for Astrophysics, retrieved online 3 May 2009, [https://web.archive.org/web/20091122010157/http://www.cfa.harvard.edu/iau/pressinfo/100PHAs.html archived] 22 November 2009.

The only object that has ever been rated at 4 on the Torino Scale (since downgraded), the Aten asteroid (99942) Apophis, has an Earth MOID of {{convert|0.00026|AU|km mi|abbr=on|lk=on}}. This is not the smallest Earth MOID in the catalogues; many bodies with a small Earth MOID are not classed as PHO's because the objects are less than roughly 140 meters in diameter (or absolute magnitude, H > 22). Earth MOID values are generally more practical for asteroids less than 140 meters in diameter as those asteroids are very dim and often have a short observation arc with a poorly determined orbit. As of September 2023, there have been seven objects detected and their Earth-MOID calculated before the Earth impact.[https://newton.spacedys.com/neodys/index.php?pc=4.5 List of Prior Impacts], NEODyS, retrieved 23 September 2023. The first two objects that were detected and had their Earth-MOID calculated before Earth impact were the small asteroids {{mpl|2008 TC|3}} and 2014 AA. 2014 AA is listed with a MOID of {{convert|0.00000045|AU|km mi|abbr=on}},[https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2014AA JPL SBDB: 2014 AA] (Earth impactor on 1 January 2014) and is the second smallest MOID calculated for an Apollo asteroid after {{mpl|2020 QY|2}} with an Earth-MOID of {{convert|0.00000039|AU|km mi|abbr=on}}.[https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2020QY2 JPL SBDB: 2020 QY2] (Near-Earth asteroid roughly 2–meters in diameter)

class="wikitable sortable" |+Potentially hazardous asteroids with Earth MOID < 0.0004 AU (~60,000 km or ~5 Earth diameters) include:
Object	Earth MOID (AU)	Size (m) (approximate)	(H)
{{mpl|2016 FG|60}}	{{convert|0.000076|AU|km mi|abbr=on|lk=on}}	align="center"|300	align="center"|21.1
{{mpl|(177049) 2003 EE|16}}	{{convert|0.000107|AU|km mi|abbr=on}}	align="center"|320	align="center"|19.8
{{mpl|2012 HZ|33}}	{{convert|0.000131|AU|km mi|abbr=on}}	align="center"|260	align="center"|20.4
{{mpl|2010 JE|88}}	{{convert|0.000148|AU|km mi|abbr=on}}	align="center"|180	align="center"|21.5
{{mpl|(137108) 1999 AN|10}}	{{convert|0.000153|AU|km mi|abbr=on}}	align="center"|1300	align="center"|17.9
{{mpl|2022 BX|1}}	{{convert|0.000177|AU|km mi|abbr=on}}	align="center"|170	align="center"|21.7
{{mpl|2003 EG|16}}	{{convert|0.000179|AU|km mi|abbr=on}}	align="center"|490	align="center"|19.4
{{mpl|2021 NQ|5}}	{{convert|0.000187|AU|km mi|abbr=on}}	align="center"|210	align="center"|21.2
{{mpl|(442037) 2010 PR|66}}	{{convert|0.000238|AU|km mi|abbr=on}}	align="center"|695	align="center"|19.3
{{mpl|(216985) 2000 QK|130}}	{{convert|0.000252|AU|km mi|abbr=on}}	align="center"|200	align="center"|21.3
99942 Apophis	{{convert|0.000257|AU|km mi|abbr=on}}	align="center"|370	align="center"|19.7
{{mpl|(89958) 2002 LY|45}}	{{convert|0.000261|AU|km mi|abbr=on}}	align="center"|1300	align="center"|17.2
{{mpl|(35396) 1997 XF|11}}	{{convert|0.000305|AU|km mi|abbr=on}}	align="center"|704	align="center"|17.0
162173 Ryugu	{{convert|0.000315|AU|km mi|abbr=on}}	align="center"|896	align="center"|19.6
{{mpl|(143651) 2003 QO|104}}	{{convert|0.000321|AU|km mi|abbr=on}}	align="center"|2300	align="center"|16.1
{{mpl|(85236) 1993 KH

} || {{convert|0.000335|AU|km mi|abbr=on}} ||align="center"|500 ||align="center"|18.8

|-

| {{mpl|(471240) 2011 BT|15}} || {{convert|0.000368|AU|km mi|abbr=on}} ||align="center"|150 ||align="center"|21.4

|}

class="wikitable sortable" |+Numbered periodic comets with Earth MOID < 0.02 AU (~3 million km) include:
Object	Epoch	Earth MOID (AU)
3D/Biela	1832	{{convert|0.0005|AU|km mi LD|abbr=on|lk=on}}
109P/Swift-Tuttle	1995	{{convert|0.0009|AU|km mi LD|abbr=on}}
55P/Tempel–Tuttle	1998	{{convert|0.0085|AU|km mi LD|abbr=on}}
255P/Levy	2007	{{convert|0.0088|AU|km mi LD|abbr=on}}
15P/Finlay	2015	{{convert|0.0092|AU|km mi LD|abbr=on}}
73P–BW	2022	{{convert|0.0093|AU|km mi LD|abbr=on}}[https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?des=73P-BW JPL SBDB: 73P-BW] (Short-lived comet fragment)
252P/LINEAR	2016	{{convert|0.0122|AU|km mi LD|abbr=on}}
460P/PanSTARRS	2016	{{convert|0.0163|AU|km mi LD|abbr=on}}
289P/Blanpain	2019	{{convert|0.0165|AU|km mi LD|abbr=on}}
21P/Giacobini–Zinner	2017	{{convert|0.0179|AU|km mi LD|abbr=on}}

class="wikitable sortable" |+Some well known Main-belt asteroids with Earth MOID < 1 AU
Object	Earth MOID (AU)
6 Hebe	{{Convert|0.975|AU|e6km e6mi LD|abbr=unit|lk=on}}
7 Iris	{{Convert|0.850|AU|e6km e6mi LD|abbr=unit}}
8 Flora	{{Convert|0.873|AU|e6km e6mi LD|abbr=unit}}
12 Victoria	{{Convert|0.824|AU|e6km e6mi LD|abbr=unit}}
18 Melpomene	{{Convert|0.811|AU|e6km e6mi LD|abbr=unit}}
84 Klio	{{Convert|0.798|AU|e6km e6mi LD|abbr=unit}}
228 Agathe	{{Convert|0.657|AU|e6km e6mi LD|abbr=unit}}