Why do some planets have thick atmospheres and others almost none?

It depends on a planet's gravity, temperature, and history of outgassing and escape; massive, cooler planets retain gas more easily, while small, hot, or unmagnetized bodies lose their atmospheres to space.

Are there familiar landforms on other worlds?

Yes, dunes, river-like channels, volcanoes, and impact craters appear across the Solar System, shaped by the same physics as on Earth but under different gravity and materials.

Planetary Atmospheres and Surfaces

The gaseous envelopes and the landscapes of planets and moons, and the processes that couple them across the Solar System.

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Definition

Planetary atmospheres and surfaces is the comparative study of the gaseous envelopes of planets and moons, their surfaces, and the processes that shape and connect them.

Scope

This area covers the atmospheres of planets and moons and the surfaces with which they interact, treated comparatively. It includes atmospheric composition, structure, circulation, and climate; the escape and evolution of atmospheres over geological time; and the surface processes that shape landforms, including wind-driven and water-driven erosion and deposition. By comparing diverse worlds, from thick-atmosphere Venus and Titan to airless bodies, the area isolates the physical principles governing atmospheres and surfaces in general.

Sub-topics

Core questions

What controls the composition, structure, and circulation of planetary atmospheres?
How do atmospheres form, escape, and evolve over a planet's lifetime?
What processes sculpt planetary surfaces into their observed landforms?
How do atmospheres and surfaces exchange material and influence each other?

Key theories

Radiative-convective atmospheric structure: The vertical temperature structure of an atmosphere is set by the balance between radiative transfer and convection, defining tropospheres, stratospheres, and the greenhouse warming of the surface.
Comparative surface processes: The same physical processes, impact, volcanism, tectonics, and erosion by wind, water, or ice, operate across planetary surfaces with outcomes that depend on gravity, atmosphere, and materials.

Clinical relevance

Atmospheres and surfaces are where planetary processes become observable and where climate and habitability are determined, making them central to interpreting both Solar System worlds and exoplanets.

History

Comparative study of planetary atmospheres and surfaces grew from telescopic observation to spacecraft exploration: probes and orbiters measured the atmospheres of Venus, Mars, the giant planets, and Titan, while imaging and landed missions revealed dunes, channels, and volcanic and impact landforms across the Solar System, unifying these phenomena under common physical theory.

Debates

Drivers of long-term planetary climate change: How orbital, volcanic, escape, and surface-feedback processes combine to drive long-term climate change on planets like Mars is an area of active investigation.

Key figures

Fredric Taylor
H. Jay Melosh
Andrew Ingersoll
James Pollack

Seminal works

taylor2010
melosh2011

Frequently asked questions

Why do some planets have thick atmospheres and others almost none?: It depends on a planet's gravity, temperature, and history of outgassing and escape; massive, cooler planets retain gas more easily, while small, hot, or unmagnetized bodies lose their atmospheres to space.
Are there familiar landforms on other worlds?: Yes, dunes, river-like channels, volcanoes, and impact craters appear across the Solar System, shaped by the same physics as on Earth but under different gravity and materials.