Minimum orbit intersection distance

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Measure of close approach in astronomy

title: "Minimum orbit intersection distance" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["near-earth-objects", "space-hazards", "orbits", "astrodynamics", "solar-system"] description: "Measure of close approach in astronomy" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/Minimum_orbit_intersection_distance" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Measure of close approach in astronomy ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/9/9e/4953_DYK.svg" caption="The orbit of [[(4953) 1990 MU]], 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. 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.

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.

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 0.00026 AU. 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. The first two objects that were detected and had their Earth-MOID calculated before Earth impact were the small asteroids and 2014 AA. 2014 AA is listed with a MOID of 0.00000045 AU, and is the second smallest MOID calculated for an Apollo asteroid after with an Earth-MOID of 0.00000039 AU.

::data[format=table title="[[Potentially hazardous asteroid]]s with Earth MOID < 0.0004 AU (~60,000 km or ~5 [[Earth radius|Earth diameters]]) include:"] | Object | Earth MOID (AU) | Size (m) (approximate) | (H) | |---|---|---|---| | | 0.000076 AU | 300 | 21.1 | | | 0.000107 AU | 320 | 19.8 | | | 0.000131 AU | 260 | 20.4 | | | 0.000148 AU | 180 | 21.5 | | | 0.000153 AU | 1300 | 17.9 | | | 0.000177 AU | 170 | 21.7 | | | 0.000179 AU | 490 | 19.4 | | | 0.000187 AU | 210 | 21.2 | | | 0.000238 AU | 695 | 19.3 | | | 0.000252 AU | 200 | 21.3 | | 99942 Apophis | 0.000257 AU | 370 | 19.7 | | | 0.000261 AU | 1300 | 17.2 | | | 0.000305 AU | 704 | 17.0 | | 162173 Ryugu | 0.000315 AU | 896 | 19.6 | | | 0.000321 AU | 2300 | 16.1 | | | 0.000335 AU | 500 | 18.8 | | | 0.000368 AU | 150 | 21.4 | ::

::data[format=table title="[[List of numbered comets|Numbered periodic comets]] with Earth MOID < 0.02 AU (~3 million km) include:"] | Object | Epoch | Earth MOID (AU) | |---|---|---| | 3D/Biela | 1832 | 0.0005 AU | | 109P/Swift-Tuttle | 1995 | 0.0009 AU | | 55P/Tempel–Tuttle | 1998 | 0.0085 AU | | 255P/Levy | 2007 | 0.0088 AU | | 15P/Finlay | 2015 | 0.0092 AU | | 73P–BW | 2022 | 0.0093 AU | | 252P/LINEAR | 2016 | 0.0122 AU | | 460P/PanSTARRS | 2016 | 0.0163 AU | | 289P/Blanpain | 2019 | 0.0165 AU | | 21P/Giacobini–Zinner | 2017 | 0.0179 AU | ::

::data[format=table title="Some well known [[Main-belt asteroid]]s
with Earth MOID < 1 AU"] | Object | Earth MOID (Asteróide) | |---|---| | 6 Hebe | 0.975 AU | | 7 Iris | 0.850 AU | | 8 Flora | 0.873 AU | | 12 Victoria | 0.824 AU | | 18 Melpomene | 0.811 AU | | 84 Klio | 0.798 AU | | 228 Agathe | 0.657 AU | ::

References

|title=JPL Small-Body Database Search Engine: Group: PHA and Orbit Constraint: Earth MOID |type=currently defined at an epoch of 2023-Sep-13 |publisher=JPL Solar System Dynamics |url=https://ssd.jpl.nasa.gov/tools/sbdb_query.html |access-date=2023-09-20}}

|type=last observation: 2020-06-17; arc: 4.29 years |title=JPL Small-Body Database: (2016 FG60) |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2016FG60 |publisher=Jet Propulsion Laboratory |archive-url=https://web.archive.org/web/20190528050554/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2016FG60 |archive-date=2019-05-28 |url-status=live |accessdate=2023-09-23}}

References

  1. [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.
  2. 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.
  3. 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.
  4. [https://newton.spacedys.com/neodys/index.php?pc=4.5 List of Prior Impacts], NEODyS, retrieved 23 September 2023.
  5. [https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2014AA JPL SBDB: 2014 AA] (Earth impactor on 1 January 2014)
  6. [https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2020QY2 JPL SBDB: 2020 QY2] (Near-Earth asteroid roughly 2–meters in diameter)
  7. [https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?des=73P-BW JPL SBDB: 73P-BW] (Short-lived comet fragment)
  8. Prado, Antônio F. B. A.. (2013-10-17). "Mapeamento de órbitas em torno do asteróide 2001SN263". SBMAC.

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