100-C 25-C 50-C 75-C C+M 50-C+M C+Y 50-C+Y M+Y 50-M+Y 100-M 25-M 50-M 75-M 100-Y 25-Y 50-Y 75-Y 100-K 25-K 25-19-19 50-K50-40-40 75-K 75-64-64

CHAPTER 16

Mars: Surface

and Interior

Michael H. Carr

U. S. Geological Survey

Menlo Park, California

1. Mars Exploration 5. Tectonics 9. The View from the Surface


2. General Characteristics 6. Canyons 10. Summary


3. Impact Cratering 7. Erosion and Deposition Bibliography


4. Volcanism 8. Poles

M

ars, the outermost of the four terrestrial planets—
Mercury, Venus, Earth, and Mars—is intermediate
in size between Earth and the Moon. The terrestrial plan-
ets all have solid surfaces, and on these surfaces is preserved
a partial record of how each planet has evolved. Successive
events, such as volcanic eruptions or meteorite impacts,
both create a new record and partly destroy the old. The
task of the geologist is to reconstruct the history of the planet
from what is preserved at the surface. Both Mercury and the
Earth’s moon appear to have become geologically inactive
early in their history so most of the preserved record dates
from very early in the history of the solar system prior to
3.5 billion years ago. The geologic record on Venus is rela-
tively young, most of the surface apparently having formed
in the last half billion years. The record on Earth is also
mostly young although ancient records are preserved on
some continents. On Mars we have a record that spans al-
most the entire history of the solar system. Although much
of the martian surface dates back to the first billion years,
volcanism, tectonism, fluvial activity, glaciation, and so forth
appear to have continued at a low rate until the recent geo-
logic past so that we can follow the evolution of the planet
for almost its entire history.
Our knowledge of the geologic evolution of the Earth
has been largely derived from the study of the lithology,
chemistry, mineralogy, and distribution of rocks at the sur-
face. Geomorphology has played a relatively minor role.

On Mars, however, much of what we know about its ge-

ology is derived from the morphology of the surface. Even

though the geomorphologic data are being increasingly sup-

plemented by information from martian meteorites and lan-

ders on the surface, our understanding is still largely based

on the appearance of the surface from orbit, and this is the

main subject of this chapter.

1. Mars Exploration

The modern era of Mars exploration began on July 14, 1965,

when theMariner 4spacecraft flew by the planet and trans-

mitted to Earth 22 close-up pictures of the planet, with res-

olutions of several kilometers. Prior to that time, we were

dependent on telescopic observations, whose resolution at

best is 100–200 kilometers, and which reveal no topogra-

phy, only surface markings. We knew from the telescopic

observations that Mars has a thin CO 2 atmosphere, polar

caps that advance and recede with the seasons, and surface

markings that undergo annual and secular change, but ge-

ologic studies of the planet could realistically begin only

when we acquired spacecraft data.

TheMariner 4pictures revealed an ancient surface that

resembled the lunar highlands. These results were disap-

pointing because it had been speculated that Mars, which

has an atmosphere and is larger than the Moon, might be

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