Knowra Moon (astronomy) Moon (astronomy) A natural satellite bound by gravity to a planet, dwarf planet, or smaller Solar System body. Moons range from captured asteroids to worlds with atmospheres, subsurface oceans, and geological activity.
Orbital resonance : A configuration in which orbiting bodies exert regular, repeating gravitational influences on one another. Resonances can stabilize moon systems and drive tidal heating, as in Jupiter’s inner large moons.
Earth's Moon : Earth’s sole natural satellite, a rocky world with a large iron-poor body and a heavily cratered surface. It is the closest and most extensively studied example of a natural satellite.
Giant-impact hypothesis : The hypothesis that Earth’s Moon formed from debris ejected by a collision between the young Earth and a large impactor. It is the leading explanation for the origin of Earth’s unusually large moon relative to its planet.
Lunar exploration : Robotic and crewed investigation of Earth’s Moon using spacecraft, landers, rovers, and human missions. The Moon is the only natural satellite visited by humans and a major target for sustained exploration.
Planet : A celestial body that orbits a star, is massive enough for gravity to make it nearly round, and has cleared its orbital neighborhood. Unlike a moon, a planet orbits a star directly and meets the recognized criteria for planetary status.
Tidal locking : A state in which a body's rotation period matches its orbital period, keeping one side facing its companion. Many moons became tidally locked to their planets through long-term tidal interactions.
Io : Jupiter’s moon and the most volcanically active known world in the Solar System. Its extreme volcanism shows how gravitational tides can power a moon’s geology.
Circumplanetary disk : A rotating disk of gas and solids surrounding a forming planet. Large regular moon systems can assemble from material in these disks, much as planets form around stars.
Europa Clipper : A NASA spacecraft mission launched in 2024 to investigate Europa’s habitability through repeated flybys. It will map Europa’s surface and measure properties relevant to its subsurface ocean.
Dwarf planet : A nearly round body orbiting the Sun that has not cleared its orbital neighborhood and is not a satellite. A dwarf planet can itself host moons, while remaining distinct from its satellites.
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