icybody

Icybody is a term used in planetary science to refer to a natural astronomical object whose mass is dominated by volatile ices, such as water ice, methane ice, ammonia ice, or carbon dioxide ice. Icy bodies are most common in the outer solar system but can be found in distant regions such as the Oort cloud. The term encompasses a range of objects, including comets, centaurs, trans-Neptunian objects, dwarf planets with substantial ice, and icy moons.

Composition and structure: Surfaces often display a mix of water ice and other volatiles. Ice may be crystalline or amorphous, influenced by temperature, radiation, and internal heating. Interiors may consist of a rocky core with an icy mantle, and in some cases sub-surface oceans. Activity occurs when ices sublimate or melt, producing comas, tails, jets, or cryovolcanic plumes.

Formation and distribution: Icy bodies formed beyond the solar system’s snow line, where ices could condensate with dust. Over time, gravitational interactions distributed them into the Kuiper belt, Oort cloud, and around giant planets. Icy bodies preserve information about the conditions of the early solar system and the distribution of volatile compounds.

Observation and exploration: Icy bodies are studied via ground-based telescopes, space telescopes, and spacecraft flybys or orbiters. Techniques include spectroscopy to identify ices, thermal infrared measurements to determine temperatures and compositions, and occultations to measure size. Some missions have returned data and observed plumes, such as Cassini–Huygens at Enceladus and Rosetta at comet 67P.

Notable examples: Comets such as Halley’s Comet are classic icy bodies; Pluto and its moon Charon are icy dwarf planet systems; Enceladus and Triton show active icy surfaces; many trans-Neptunian objects, such as Pluto, Eris, and Haumea, are composed largely of ice. The study of icy bodies informs models of solar system formation and the delivery of volatiles to the inner planets.