Planetary Science Glossary

The gradual growth of a planetary body by gravitational accumulation of surrounding material from a protoplanetary disk.

The ratio of reflected to incident light on a surface, expressed as a value between 0 and 1.

A small rocky body orbiting the Sun, most commonly found in the asteroid belt between Mars and Jupiter.

A small icy body that, when close to the Sun, develops a visible atmosphere (coma) and sometimes a tail of gas and dust.

The study of planetary bodies by comparing their physical and chemical properties to derive general principles of planetary behavior.

Volcanic activity involving the eruption of volatile ices such as water, ammonia, or methane from the interior of an icy body.

The process by which a planetary body separates into concentric layers of different density and composition, such as a metallic core and silicate mantle.

A planet that orbits a star outside our solar system, detected via methods such as the transit method or radial velocity.

The distance from a star beyond which volatile compounds can condense into solid ices, influencing the types of planets that form.

A large planet composed predominantly of hydrogen and helium without a well-defined solid surface, such as Jupiter and Saturn.

The orbital region around a star where conditions may permit liquid water to exist on a planet's surface.

A giant planet composed largely of elements heavier than hydrogen and helium, particularly water, ammonia, and methane. Uranus and Neptune are ice giants.

A region of icy bodies beyond Neptune's orbit, extending from about 30 to 55 AU from the Sun, home to dwarf planets like Pluto.

The region surrounding a planet that is controlled by the planet's magnetic field, deflecting solar wind particles.

The visible streak of light produced when a small piece of space debris burns up upon entering a planetary atmosphere.

A fragment of a meteoroid or asteroid that survives passage through the atmosphere and reaches the surface of a planet or moon.

A hypothetical spherical shell of icy bodies at the outermost edges of the solar system, believed to be the source of long-period comets.

A situation in which two orbiting bodies exert regular gravitational influence on each other due to their orbital periods being in a ratio of small integers.

A solid object in a protoplanetary disk, typically ranging from meters to kilometers in size, that serves as a building block for planet formation.

A rotating circumstellar disk of gas and dust from which planets and other bodies form around a young star.

The layer of loose, unconsolidated material covering the solid bedrock of a planetary body, formed by impacts, weathering, and other surface processes.

The minimum orbital distance at which a satellite held together only by gravity can survive without being torn apart by tidal forces from the primary body.

A continuous stream of charged particles (mostly protons and electrons) emitted by the Sun's corona into interplanetary space.

A planet composed primarily of silicate rocks and metals with a solid surface. Mercury, Venus, Earth, and Mars are the solar system's terrestrial planets.

The internal heating of a planetary body caused by frictional dissipation of tidal forces from a nearby massive body.