468 PART 4^ |^ THE SOLAR SYSTEM
(■ Figure 22-4) that bounce the radar signal around
and shoot it back the way it came. Th ese rough lava
fl ows look very bright in radar maps. Certain mineral
deposits are also bright. Radar maps do not show how
the surface would look to human eyes but rather pro-
vide information about altitude, roughness, and, in
some cases, chemical composition.
Th e big map in ■ Figure 22-5 is a map of all of
Venus except the polar regions. (Note that this map
has been color coded by altitude.) By international
agreement, the names of celestial bodies and features
on celestial bodies are assigned by the International
Astronomical Union, which has decided that all
names on Venus should be feminine. Th ere are only a
few exceptions, such as the mountain Maxwell
Montes, 50 percent higher than Mount Everest. It was discov-
ered during early Earth-based radar mapping and named for
James Clark Maxwell, the 19th-century physicist who fi rst
described electromagnetic radiation. Alpha Regio and Beta
Regio, later found to be volcanic peaks, were also discovered
by radar before the naming convention was adopted. Other
names on Venus are feminine, such as the highland regions
Ishtar Terra and Aphrodite Terra, named for the Babylonian
and Greek goddesses of love. Th e insets in Figure 22-5 show
roughness and composition of the surface in maps made by
diff erent satellites and color coded in diff erent ways. All of
these radar maps paint a picture of a hot, violent, desert
world.
Radar maps show that the surface of Venus consists of
low, rolling plains and highland regions. Th e rolling plains
appear to be large-scale smooth lava fl ows, and the highlands
are regions of deformed crust.
Just as in the case of the lunar landscape, craters are the
key to fi guring out the age of the surface. With nearly 1000
impact craters on its surface, Venus has more craters than
The horizon of Venus
is visible at the top
corners of the image.Edge of
spacecraftInstrument cover
ejected after landingAtla RegioBeta RegioAtla RegioBeta RegioRadar map■ Figure 22-2
The Venera lander touched down on Venus in 1982 and carried
a camera that swiveled from side to side to photograph the
surface. The orange glow is produced by the thick atmosphere;
when that is corrected to produce the view as it would be under
white light, you can see that the rocks are dark gray. Isotopic
analysis suggests they are basalts.
■ Figure 22-3
Venus without its clouds: This mosaic of Magellan radar maps has been
given an orange color to mimic the sunset coloration of daylight at the
surface of the planet. The image shows scattered impact craters and
volcanic regions such as Beta Regio and Atla Regio. (NASA)