gasgigant

Gasgigant is a term used in planetary science to classify planets whose mass is dominated by light gases, primarily hydrogen and helium, resulting in a thick gaseous envelope and little to no solid surface. In many contexts the term is synonymous with gas giant, particularly when distinguishing from ice giants and terrestrial planets.

They are among the largest planets, radii typically 1–2 times that of Jupiter and masses from about 0.3 to several tens of Jupiter masses. They feature deep atmospheres with cloud layers of ammonia, water, and hydrocarbons, extreme winds, and strong internal heat.

Internal structure is thought to consist of a possible rocky or icy core surrounded by metallic hydrogen, with a molecular hydrogen envelope. The exact arrangement and composition vary by formation history and age; heat from formation can produce a hotter, puffed-up exterior in young systems.

Formation and occurrence: Gasgigants form in gas-rich protoplanetary disks through core accretion or disk instability, and are common around sun-like stars. In our solar system, Jupiter and Saturn are archetypal gasgigants; Uranus and Neptune are ice giants rather than gas-dominated giants.

Observation and research: Gasgigants are detected by transit and radial-velocity methods, with direct imaging and microlensing contributing for distant or young objects. Their atmospheres are studied via spectroscopy, revealing weather patterns, chemical composition, and thermal structure; many display inflated radii and strong magnetic fields.

Impact and context: As the most massive planets in many systems, gasgigants influence the dynamical evolution of their orbits and moons, shape circumstellar environments, and help inform theories of planet formation and migration.