mainbelt

Main belt, sometimes written as mainbelt, refers to the region of the Solar System between Mars and Jupiter that contains a large population of rocky bodies known as asteroids. Most belt objects orbit the Sun in a near-plane, with modest orbital eccentricities, and collectively they span a wide range of sizes.

The belt lies roughly 2.1 to 3.3 astronomical units from the Sun and contains millions of asteroids; the total mass is estimated at about 2 to 4 × 10^21 kilograms, a small fraction of the Moon’s mass.

The largest object is Ceres, a dwarf planet about 940 kilometers in diameter. Among others are Vesta, Pallas, and Hygiea. The belt shows a mix of compositions, with carbonaceous (C-type), silicaceous (S-type), and metal-rich (M-type) bodies, though composition varies by region.

Its orbital structure includes gaps known as Kirkwood gaps, created by mean-motion resonances with Jupiter that clear or destabilize orbits. Numerous collisional families, formed by past impacts, populate the belt with fragments and can be traced to common origins.

Formation and significance: The belt formed from the early solar nebula but did not coalesce into a planet because of Jupiter’s perturbations. Studying belt objects helps scientists understand planetary formation, and missions such as Dawn have explored Vesta and Ceres. Belt material also contributes meteorites found on Earth.