Editing List of minor-planet groups (section)

==The asteroid belt==
{{main|Asteroid belt}}
[[File:Kirkwood Gaps.svg|thumb|[[Histogram]] showing the four most prominent [[Kirkwood gap]]s and a possible division into inner, middle and outer [[main-belt]] asteroids:<br />{{legend2|#005aff|border=1px solid #333|inner main-belt ([[Semi-major axis|''a'']] &lt; 2.5 [[Astronomical unit|AU]])}}<br />{{legend2|#ffa500|border=1px solid #222|middle main-belt (2.5 AU &lt; ''a'' &lt; 2.82 AU)}}<br />{{legend2|#55d400|border=1px solid #333|outer main-belt (''a'' &gt; 2.82 AU}}]]
[[File:Main belt i vs a.png|thumb|Asteroid groups out to the orbit of Jupiter. The asteroid belt is shown in red]]

The overwhelming majority of known asteroids have orbits lying between the orbits of [[Mars]] and [[Jupiter]], roughly between 2 and 4&nbsp;[[astronomical unit|AU]]. These could not form a planet due to the gravitational influence of Jupiter. Jupiter's gravitational influence, through [[orbital resonance]], clears [[Kirkwood gap]]s in the asteroid belt, first recognised by [[Daniel Kirkwood]] in 1874.

The region with the densest concentration (lying between the Kirkwood gaps at 2.06 and 3.27&nbsp;AU, with [[eccentricity (orbit)|eccentricities]] below about 0.3, and inclinations smaller than 30°) is called the [[asteroid belt]]. It can be further subdivided by the Kirkwood Gaps into the:
* '''Inner asteroid belt''', inside of the strong Kirkwood gap at 2.50&nbsp;AU due to the 3:1 Jupiter [[orbital resonance]]. The largest member is [[4&nbsp;Vesta]].
** It apparently also includes a group called the main-belt I asteroids which have a semi-major axis between 2.3&nbsp;AU and 2.5&nbsp;AU and an inclination of less than 18°.
* '''Middle''' (or intermediate) '''asteroid belt''', between the 3:1 and 5:2 Jupiter orbital resonances, the latter at 2.82&nbsp;AU. The largest member is [[Ceres (dwarf planet)|Ceres]]. This group is apparently split into the:
** Main-belt IIa asteroids which have a semi-major axis between 2.5&nbsp;AU and 2.706&nbsp;AU and an inclination less than 33°.
** Main-belt IIb asteroids which have a semi-major axis between 2.706&nbsp;AU and 2.82&nbsp;AU and an inclination less than 33°.
* '''Outer asteroid belt''' between the 5:2 and 2:1 Jupiter orbital resonances. The largest member is [[10&nbsp;Hygiea]]. This group is apparently split into the:
** Main-belt IIIa asteroids which have a semi-major axis between 2.82&nbsp;AU and 3.03&nbsp;AU, an eccentricity less than .35, and an inclination less than 30°.
** Main-belt IIIb asteroids which have a semi-major axis between 3.03&nbsp;AU and 3.27&nbsp;AU, an eccentricity less than .35, and an inclination less than 30°.

===Other groups out to the orbit of Jupiter===

There are a number of more or less distinct asteroid groups outside the asteroid belt, distinguished either by mean distance from the Sun, or particular combinations of several orbital elements:
* The [[Hungaria family|Hungaria asteroid]]s, with a mean orbital radius between 1.78&nbsp;AU and 2&nbsp;AU, an eccentricity less than 0.18, and inclination between 16° and 34°. Named after [[434&nbsp;Hungaria]], these are just outside Mars's orbit, and are possibly attracted by the 9:2 Jupiter resonance or the 3:2 Mars resonance.
* The [[Phocaea family|Phocaea asteroid]]s, with a mean orbital radius between 2.25&nbsp;AU and 2.5&nbsp;AU, an eccentricity greater than 0.1, and inclination between 18° and 32°. Some sources group the Phocaeas asteroids with the Hungarias, but the division between the two groups is real and caused by the 4:1 resonance with Jupiter. Named after [[25&nbsp;Phocaea]].
* The [[Alinda asteroid]]s have a mean orbital radius of 2.5&nbsp;AU and an eccentricity between 0.4 and 0.65 (approximately). These objects are held by the 3:1 resonance with Jupiter and a 4:1 resonance with [[Earth]]. Many Alinda asteroids have perihelia very close to Earth's orbit and can be difficult to observe for this reason. Alinda asteroids are ''not'' in stable orbits and eventually will collide either with Jupiter or terrestrial planets. Named after [[887&nbsp;Alinda]].
* The [[Pallas family]] asteroids have a mean orbital radius between 2.7 and 2.8&nbsp;AU and an inclination between 30° and 38°. Named after [[2&nbsp;Pallas]].
* The [[Griqua group|Griqua asteroid]]s have an orbital radius between 3.1&nbsp;AU and 3.27&nbsp;AU and an eccentricity greater than 0.35. These asteroids are in stable 2:1 [[libration]] with Jupiter, in high-inclination orbits. There are about 5 to 10 of these known so far, with [[1362&nbsp;Griqua]] and [[8373&nbsp;Stephengould]] the most prominent.
* The [[Cybele asteroids]] have a mean orbital radius between 3.27&nbsp;AU and 3.7&nbsp;AU,<ref name="Carruba-2013" /> an eccentricity less than 0.3,<ref name=tanton /> and an inclination less than 30°.<ref name="Carruba-2013" /> This group appears to cluster around the 7:4 resonance with Jupiter. Named after [[65&nbsp;Cybele]].<ref name=tanton />
* [[Hilda group|Hilda asteroid]]s have a mean orbital radius between 3.7&nbsp;AU and 4.2&nbsp;AU, an eccentricity greater than 0.07, and an inclination less than 20°. These asteroids are in a 3:2 resonance with Jupiter. Named after [[153&nbsp;Hilda]].
* The [[Thule asteroid]]s are in a 4:3 resonance with Jupiter and the group is known to consist of [[279&nbsp;Thule]], {{mpl|(186024) 2001 QG|207}}, and {{mpl|(185290) 2006 UB|219}}.<ref name="Broz-2008" />
* The [[Jupiter trojan]]s have a mean orbital radius between 5.05&nbsp;AU and 5.4&nbsp;AU, and lie in elongated, curved regions around the two [[Lagrangian point]]s 60° ahead and behind of Jupiter. The leading point, {{L4}}, is called the [[Greek camp]] and the trailing {{L5}} point is called the [[Trojan camp]], after the two opposing camps of the legendary [[Trojan War]]; with one exception apiece, objects in each node are named for members of that side of the conflict. [[617&nbsp;Patroclus]] in the Trojan camp and [[624&nbsp;Hektor]] in the Greek camp are "misplaced" in the enemy camps.

There is a forbidden zone between the Hildas and the Trojans (roughly 4.05&nbsp;AU to 4.94&nbsp;AU). Aside from [[279&nbsp;Thule]] and 228 objects in mostly unstable-looking orbits, Jupiter's gravity has swept everything out of this region.