Small Solar System body

A Solar System object that is neither a planet, dwarf planet, nor natural satellite. The category includes most asteroids, comets, and trans-Neptunian objects.

International Astronomical Union: The international organization that coordinates professional astronomy and defines astronomical nomenclature. Its 2006 definitions established the categories that exclude planets, dwarf planets, and natural satellites.
Asteroid: A small rocky or metallic body that orbits the Sun. Most asteroids fall within the small-body category rather than the planet categories.
Yarkovsky effect: A force on a rotating body caused by the anisotropic emission of absorbed thermal radiation. This subtle force can shift asteroid orbits and influence delivery into near-Earth space.
Hayabusa2: A Japanese spacecraft that returned samples from the near-Earth asteroid Ryugu in 2020. Its samples let researchers study a primitive small body directly in laboratories.
Late Heavy Bombardment: A proposed interval of elevated impact rates in the inner Solar System roughly 3.9 billion years ago. The timing and intensity of early impacts constrain models of small-body populations.
Planet: A celestial body that orbits the Sun, is nearly round, and has cleared its orbital neighborhood. Planets are explicitly excluded from the small-body category.
Comet: An icy Solar System body that releases gas and dust when heated near the Sun. Comets are small bodies whose activity makes them distinct from most asteroids.
Cometary activity: The release of gas and dust from a comet as solar heating drives volatile materials from its surface. Outgassing creates comae and tails and can also change a comet’s motion.
OSIRIS-REx: A NASA mission that collected samples from asteroid Bennu and returned them to Earth in 2023. Bennu’s returned material provides evidence about small-body composition and Solar System history.
Origin of Earth's water: The scientific question of how water accumulated on Earth during its formation and later history. Small bodies may have delivered some terrestrial water, but their relative contributions remain debated.

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