Definition
A terrestrial planet with a thick and toxic atmosphere is a rocky body whose surface is covered by a heavy gaseous layer. This envelope acts as a thermal and chemical insulator, trapping energy and profoundly altering surface conditions.
Structure
Beneath its thick atmosphere, the planet has a solid crust made of silicates and metals, overlying a mantle and an inner core. The atmosphere, rich in opaque and corrosive gases, extends through several layers, from the lower troposphere to the upper mesosphere.
Atmosphere and composition
The main gases often include carbon dioxide, nitrogen, and traces of sulfur compounds. This composition creates a strong greenhouse effect, trapping heat and producing extreme surface temperatures. The clouds are dense, reflective, and limit visibility from space.
Surface and conditions
Under this heavy atmosphere, the surface endures immense pressure and constant heat. The landscape may feature volcanic plains, mountains, and tectonic fractures. Interactions between the crust and the atmosphere are slow but continuous, affecting the planet’s overall chemistry.
Evolution
Such a planet results from an evolution where volatile gases accumulated instead of being absorbed or dissipated. Volcanism, limited atmospheric loss, and proximity to an active star maintain the density and toxicity of the gaseous envelope.
Limits and observation
The extreme conditions prevent any known form of life and make direct exploration difficult. Observation relies mainly on spectroscopy and radar, allowing analysis of chemical composition and topography beneath the opaque clouds.