How do scientists map a planet they cannot visit?

They use orbiting spacecraft that image the surface, measure its topography, and analyze reflected and emitted light to map composition, building detailed geological maps from afar.

What landforms are common across the Solar System?

Impact craters are nearly universal, and volcanoes, fault systems, and wind-blown dunes appear on many bodies, shaped by the same basic processes under different conditions.

Planetary Surfaces and Landforms

The varied landscapes of planets and moons, and how their landforms record the processes that built and modified them.

Definition

Planetary surfaces and landforms is the study of the morphology of the solid surfaces of planets and moons and of the geological processes recorded in their landforms.

Scope

This topic covers the morphology of planetary surfaces and the interpretation of landforms across the Solar System. It treats the major surface-shaping processes, impact, volcanic, tectonic, and erosional, and the distinctive landforms each produces, along with the remote-sensing and mapping methods used to study surfaces. It also covers how landform assemblages and crater records are combined to reconstruct the geological history and relative ages of planetary terrains.

Core questions

What processes create the major landforms seen on planetary surfaces?
How can surface morphology be used to reconstruct a body's geological history?
How do remote sensing and mapping reveal composition and topography from afar?
How do gravity, atmosphere, and materials make the same process look different on different worlds?

Key theories

Surface-process geomorphology: Planetary landforms result from a limited set of processes, impact, volcanism, tectonism, and gradation, whose products can be recognized and used to infer the history of a surface.
Stratigraphy and relative dating: Superposition relationships and crater densities establish the relative ages and sequence of geological units on a planetary surface even without returned samples.

Mechanisms

Impacts excavate craters and basins, volcanism builds plains and edifices, tectonics fractures and warps the crust, and gradational processes erode and deposit material. The resulting landforms are layered in time, so their geometry and crater densities encode the sequence and relative ages of events, read through orbital imaging, spectroscopy, altimetry, and radar.

Clinical relevance

Surface morphology is the primary record of a planet's geological evolution and the main basis for choosing and interpreting landing sites and for relating remote observations to processes.

History

Telescopic mapping of the Moon and Mars gave way to spacecraft imaging that revealed surfaces in detail: lunar orbiters and Apollo, the Viking and later Mars orbiters and rovers, Magellan's radar of Venus, and outer-planet missions all built a comparative catalogue of landforms, with geomorphologists such as Greeley systematizing planetary landscapes.

Debates

Interpreting ambiguous landforms: Some features can form by more than one process, for example channels carved by water or by lava, so distinguishing among origins from imagery alone can be contested.

Key figures

Ronald Greeley
H. Jay Melosh
Eugene Shoemaker
Michael Carr

Seminal works

melosh2011
greeley1985

Frequently asked questions

How do scientists map a planet they cannot visit?: They use orbiting spacecraft that image the surface, measure its topography, and analyze reflected and emitted light to map composition, building detailed geological maps from afar.
What landforms are common across the Solar System?: Impact craters are nearly universal, and volcanoes, fault systems, and wind-blown dunes appear on many bodies, shaped by the same basic processes under different conditions.