Page 305 - NS-2 Textbook

300 NAUTICAL SCIENCES

The best time for viewing Mars is when it is nearest
to Earth in August and September. In those months it
sometimes comes as close as 30 million miles. In Febru-
ary and March it is over 60 million miles away and much
less easily vieV\Ted. It is best seen ·when in direct opposi-
tion-in other words, when Earth is directly between the
Sun and Mars.
Many scientists of the past thought Mars capable of
supporting some kind of life. TIle Italian astronomer Gio-
vanni Schiaparelli annotmced that he had observed a se-
ries of intersecting lines on the Martian surface in 1877.
He called them canali, Italian for "channels" or "canals,"
Many people believed that the canali must have been
made by intelligent beings because they were so straight.
Or they thought that perhaps they were created by
free-flowing water, indicating that Mars could be capable
of supporting life. But subsequent observations and ex-
tensive photography from the Mariner and Viking series
of space probes definitively proved the canali to be an
illusion.
In 1969 and 1970 Mariller 6 and Mariller 7 made six-
month-long journeys to photograph Mars, looking
A photograph of a densely cratered region of the planet Mercury,
taken by a TV camera aboard Mariner 10 in 1974. The photo was specifically for life on the planet. They found no sign of
taken from a range of about 47,000 miles above the planet's living things or an environment that could support them.
surface.
TIle landscape appeared barren, and there was no evi-
dence of water.
Mari1ler 9, by extensive photography of the Martian
ution of volcanoes is also interesting. On Venus hun-
surface, revealed that large mnounts of water must have
dreds of thousands, perhaps millions, of them appear to
once washed over the planet to form great canyons, me-
be randomly distributed around its surface, rather than
distributed in groups such as in the "Ring of Fire" around andering hWldreds of miles across the surface. Today,
however, Mars has a grim, lWlarlike landscape, pock-
Earth's Pacific rim.
With its power supplies nearly depleted, Magel/ail's marked with craters.
mission ended with a dramatic plwlge into the Venusian The Martian ahnosphere contains small amounts of
oxygen and ,vater vapOl~ but not enough to sustain life as
atmosphere in October 1994, the first time an operating
we know it on Earth. It is mostly carbon dioxide, and
planetary spacecraft was intentionally destroyed. TIle
only about 1 percent as dense as Earth's-about the same
purpose of the maneuver was to gather data on Venus's
as our atmosphere 20 miles up. Thin white clouds occa-
atmosphere before Magel/all ceased to nmction.
sionally appear in the Martian atmosphere, and a veil of
So Venus, named for the Roman goddess of beauty,
is in fact a grim and lifeless inferno hidden behind its
clouds. But to us on Earth, Venus is often the brightest
object in the sky, besides the Moon and Sun. Venus shines
most brightly when it is between us and the Sun, even
though the sunlight falls on the side away from us, for
the planet is closest to us at that time.

MARS
Of all the planets in our solar system, Mars, the fourth
from the Stm and the next one beyond Earth, has aroused
the greatest interest. Named after the Roman god of war,
it is often called the "red planet." It is not as easily recog-
A view of Mars from the Mariner 9 spacecraft. Several theories have
nized as Venus or Jupiter because it is not as bright. But
been proposed to account for the channels in the middle of the pic-
Mars's red color and its rapid lllovement from V\Test to ture, but final determination of their origin will probably have to
east among the stars make it stand out in the sky. await a manned exploration mission.