Gasplanet

Gasplanet is a general term used to describe large planets whose bulk is dominated by light gaseous constituents, primarily hydrogen and helium, and that lack a well-defined solid surface. In planetary science, gas planets are contrasted with terrestrial planets, which are smaller and composed largely of rock and metal. Gas planets can possess extensive atmospheres and thick envelopes that extend over most of their radius.

Internally, gas planets are theorized to have relatively small, dense cores surrounded by gradually increasing pressure zones that transform hydrogen into metallic hydrogen in the deeper layers. The outer atmosphere features complex weather systems, strong winds, and variable cloud decks. Many gas planets also host magnetic fields generated by conducting material in their interiors. Ring systems and numerous natural satellites are common around the larger gas giants in the solar system.

Formation and classification: Gas planets form in the outer regions of protoplanetary disks where ices and gases are abundant. They grow by accreting hydrogen and helium gas onto a solid core, or, in some cases, by rapid disk instability. In our solar system, Jupiter and Saturn are the classic gas giants; Uranus and Neptune are often referred to as ice giants, a related class with more ices and a thinner gaseous envelope. Among exoplanets, a large number are gas-rich, including many hot Jupiters and warm gas giants.

Observation and significance: Gas planets are primary targets in exoplanet surveys. They produce detectable signals via planetary transits, radial velocity wobbles, direct imaging, and microlensing. Spectroscopy reveals atmospheric composition, temperature, and weather patterns. Their relatively low densities and large sizes influence planetary system dynamics and can affect the formation and migration of close-in planets.