CHAPTER 22 | COMPARATIVE PLANETOLOGY OF VENUS AND MARS 477
could not see the canals at all, but others drew maps showing
hundreds (■ Figure 22-10).
In the decades that followed Schiaparelli’s “discovery,” many
people assumed that the canals were watercourses built by an
intelligent race to carry water from the polar caps to the lower
latitudes. Much of this excitement was generated by Percival
Lowell, a wealthy Bostonian who, in 1894, founded Lowell
Observatory in Flagstaff , Arizona, principally for the study of
Mars. He not only mapped hundreds of canals but also popular-
ized his results in books and lectures. Although some astrono-
mers claimed the canals were merely illusions, by 1907 the
general public was so sure that life existed on Mars that the Wall
Street Journal suggested that the most extraordinary event of the
previous year had been “the proof by astronomical observa-
tions... that conscious, intelligent human life exists upon the
planet Mars.” Further sightings of bright clouds and fl ashes of
light on Mars strengthened this belief, and some urged that
gigantic geometrical diagrams be traced in the Sahara Desert to
signal to the Martians that Earth, too, is inhabited. All seemed to
agree that the Martians were older and wiser than humans.
Th is fascination with men from Mars was not a passing
fancy. Beginning in 1912, Edgar Rice Burroughs (author of the
Tarzan stories) wrote a series of 11 novels about the adventures
of the Earthman John Carter, lost on Mars. Burroughs made the
geography of Mars, named by Schiaparelli after Mediterranean
lands both real and mythical, into household words. He also
made his Martians small and gave them green skin.
By Halloween night of 1938, people were so familiar with
life on Mars that they were ready to believe that Earth could be
invaded. When a radio announcer repeatedly interrupted dance
music to report the landing of a spaceship in New Jersey, the
emergence of monstrous creatures, and their destruction of
whole cities, thousands of otherwise sensible people fl ed in panic,
not knowing that Orson Welles and other actors were dramatiz-
ing H. G. Wells’s book Th e War of the Worlds.
Public fascination with Mars, its canals, and its little green
men lasted right up until July 15, 1965, when Mariner 4, the
fi rst spacecraft to fl y past Mars, radioed back photos of a dry,
cratered surface and proved that there are no canals and no
Martians. Th e canals are optical illusions produced by the human
brain’s powerful ability to assemble a fi eld of disconnected marks
into a coherent image. If your brain could not do this, the photos
on these pages would be nothing but swarms of dots, and the
images on a TV screen would never make sense. Th e downside of
this is that the brain of an astronomer looking for something at
the edge of visibility is capable of connecting faint, random
markings on Mars into the straight lines of canals.
Even today, Mars holds some fascination for the general pub-
lic. Grocery store tabloids regularly run stories about a giant face
carved on Mars by an ancient race. Although planetary scientists
recognize it as nothing more than chance shadows in a photo-
graph and dismiss the issue as a silly hoax, the stories persist.
Mars is only half the diameter of Earth and probably retains
some internal heat, but the size and composition of its core are
not well known. (NASA)Celestial Profi le 6: Mars
Motion:
Average distance from the sun 1.52 AU (2.28 108 km)
Eccentricity of orbit 0.093
Inclination of orbit to ecliptic 1.9°
Average orbital velocity 24.1 km/s
Orbital period 1.881 y (687.0 days)
Period of rotation 24.62 h
Inclination of equator to orbit 25.2°Characteristics:
Equatorial diameter 6.79 103 km (0.531 D⊕)
Mass 6.42 1025 kg (0.108 M⊕)
Average density 3.94 g/cm^3 (3.3 g/cm^3 uncompressed)
Surface gravity 0.38 Earth gravity
Escape velocity 5.0 km/s (0.45 V⊕)
Surface temperature −140° to 15°C (−220° to 60°F)
Average albedo 0.16
Oblateness 0.009Personality Point:
Mars is named for the god of war. Minerva was the goddess of defensive
war, but Bullfi nch’s Mythology refers to Mars’s “savage love of violence and
bloodshed.” You can see how the planet glows blood red in the evening
sky because of iron oxides in its soil.