Asteroid

A map of planets and asteroid groups of the inner solar system. Distances from sun are to scale, object sizes are not.

Various dynamical groups of asteroids have been discovered orbiting in the inner Solar System. Their orbits are perturbed by the gravity of other bodies in the Solar System and by the Yarkovsky effect. Significant populations include:

Asteroids are commonly categorized according to two criteria: the characteristics of their orbits, and features of their reflectance spectrum.

The proportion of known asteroids falling into the various spectral types does not necessarily reflect the proportion of all asteroids that are of that type; some types are easier to detect than others, biasing the totals.

Asteroids and comets visited by spacecraft as of 2019 (except Ceres and Vesta), to scale
Artist's concept of the asteroid Psyche, the focal point of NASA's mission of the same name

Currently, several asteroid-dedicated missions are planned by NASA, JAXA, ESA, and CNSA.

Cumulative discoveries of just the near-Earth asteroids known by size, 1980–2022

Asteroids and the asteroid belt are a staple of science fiction stories. Asteroids play several potential roles in science fiction: as places human beings might colonize, resources for extracting minerals, hazards encountered by spacecraft traveling between two other points, and as a threat to life on Earth or other inhabited planets, dwarf planets, and natural satellites by potential impact.