English: This histogram clearly shows the primary Kirkwood gaps in the asteroid main belt. These gaps (labeled "4:1", "3:1", "5:2", "7:3", "2:1") are caused by mean-motion resonances between an asteroid and Jupiter. For example, the 3:1 Kirkwood gap is located where the ratio of an asteroid's orbital period to that of Jupiter is 3/1 (the asteroid completes 3 orbits for every 1 orbit of Jupiter). The effect of these mean-motion resonances is a change in the asteroid's orbital elements (particularly semimajor axis) sufficient to create these gaps in semimajor axis space. The inner main-belt (a < 2.5 AU), middle main-belt (2.5 AU < a > 2.82 AU), and outer main-belt (a > 2.82 AU) are colored in blue, orange, and green respectively. Asteroid osculating elements are from JPL SSDB (accessed 13 May 2026) https://ssd.jpl.nasa.gov/tools/sbdb_query.html.