Definition
Gigantides are massive planets primarily composed of hydrogen and helium. They are typically located in the outer regions of stellar systems and exhibit atmospheres in continuous dynamic states, with no observable solid surface.
Structure
The main structural component is a vast gaseous envelope divided into layers. Convective transport and radiative transfer alternate with depth, producing zones and cloud bands visible in the upper atmosphere.
Atmosphere and dynamics
The atmosphere shows high wind speeds and long-lasting cyclonic and anticyclonic systems. The planet’s rotation and latitudinal variation of heat flux generate zonal winds, waves, and strong shear visible in cloud bands.
Rings and satellites
Many Gigantides have ring systems composed of icy and rocky particles in Keplerian orbits. Gravitational resonances with satellites control gaps, density, and the distribution of ring material. Satellites regulate dynamical evolution through tidal interactions.
Interior
At depth, gas becomes compressed; a region of molecular hydrogen transitions to a metallic hydrogen state, which sustains strong magnetic fields through dynamo effects. The inner core is likely rocky or icy, enriched with heavy elements and subjected to extremely high pressures.
Role in stellar systems
The large mass of Gigantides modifies the orbits of neighboring bodies through migration and resonances, influencing planetary formation and system stability. Their observation provides information on accretion, migration, and the distribution of matter in circumstellar disks.