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The Planets .... brought to you by QuasArt Web Designs.
M A R S (4th planet)
Mars (Greek: Ares) is the god of War. The planet probably got this
name due to its red color; Mars is sometimes referred to as the
Red Planet. (An interesting side note: the Roman god Mars was a
god of agriculture before becoming associated with the Greek Ares;
those in favor of colonizing and terraforming Mars may prefer this
symbolism.) The name of the month March derives from Mars.
Men are supposedly from Mars.
CHAPTERS
I II III IV V VI VII VIII IX X XI
2 MOONS
INTRODUCTION
I
One of the planets in the solar system, it is the fourth
planet from the sun and orbits the sun at a distance
of about 228 million km (about 141 million mi). Mars is named for
the Roman god of war because it appears fiery red in the earth's night
sky.
Unpiloted
spacecraft from the United States, launched between 1964 and 1976,
have supplied the most detailed information on Mars. From this data,
scientists determined that the planet's atmosphere predominantly consists
of carbon dioxide ( CO2 ), with small amounts of nitrogen, oxygen,
and water vapor also present. Due to the thinness of the atmosphere,
daily temperatures often vary as much as 100 Celcius degrees (190
Fahrenheit degrees). In general, surface temperatures are too cold
and surface pressures too low for water to exist in a liquid state
on Mars, so the planet resembles a cold, high-altitude desert.
Mars is a relatively small planet, with about half the diameter of
Earth and about one-tenth Earth's mass. The force of gravity on the
surface of Mars is about one-third of that on Earth. Mars has twice
the diameter and twice the surface gravity of Earth's moon. The surface
area of Mars is almost exactly the same as the surface area of the
dry land on Earth.
The Martian day, or the time it takes Mars to rotate once on its axis,
is about a half an hour longer than an Earth day. Its year, or the
time it takes to revolve once around the sun, is about two Earth years
long. Mars has two moons, Phobos and Deimos, which are named after
the dogs of the Roman god Mars. These tiny bodies are heavily cratered
dark chunks of rock and may be asteroids captured by the gravitational
pull of Mars. Phobos orbits Mars once in less than one Martian day,
so it appears to rise in the west and set in the east, usually twice
each day. Deimos has the more ordinary habit of rising in the east
and setting in the west.
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OBSERVATION FROM
EARTH
II
Mars appears as a fairly bright, starlike object in the night sky
of Earth. It moves through Earth's sky fairly rapidly, on a timescale
of months. Because of the relative movements of Earth and Mars around
the sun, Mars appears to move backward in the sky for a short time
around opposition, when the two planets are closest. As Mars and Earth
orbit the sun, the distance between them varies from about 75 million
km (about 47 million mi) at opposition to about 375 million km (about
233 million mi) when the planets are on opposite sides of the sun.
This change in distance causes the apparent size of Mars to vary by
a factor of 5 and its brightness to vary by a factor of 25.
When Mars is viewed through a telescope, it looks like a red and orange
disk. An observer can easily see white ice caps at the north and south
poles of Mars. These caps grow and shrink throughout the Martian year,
just as the polar caps of Earth do. The darker areas of Mars's surface
may look greenish to the observer, but this is an optical illusion
caused by the contrast in color between the dark patches and brighter
areas. Scientists believe that the dark areas are regions of relatively
unweathered bare rock, while the bright areas are regions with deposits
of weathered material, especially fine dust. At certain times of the
year, usually the southern Martian spring and summer when Mars is
closest to the sun, great dust storms appear as yellow clouds. The
largest of these storms can cover the globe of Mars and last for months.
At other times white clouds of water vapor are visible. Scientists
now believe that the "canals" people observed on Mars during the 19th
century are actually another optical illusion, caused by the mind's
tendency to draw connections between irregular patches in a fuzzy
image. The Hubble Space Telescope (HST) provides the clearest Earth-based
views of Mars, and astronomers use it to study the weather on the
planet. The HST has provided images of dust storms with such detail
that scientists can pinpoint the areas on the planet in which the
storms started. The telescope also makes general studies of the atmosphere
possible. Using HST images, astronomers have determined that the atmosphere
of Mars is cooler, clearer, and drier than it was in the mid-1970s,
the last time scientists were able to monitor the atmosphere closely.
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THE INTERIOR OF MARS
III
Scientists believe that Mars's interior consists of a crust, mantle,
and core like Earth's interior (seeEarth: Composition), but they do
not know the relative sizes of these components. Because no spacecraft
has ever brought instruments that can study Mars's interior to the
planet, the only real data that scientists have about the planet's
structure are its mass, size, and the structure of the gravity field.
From that data scientists can learn some things about density in different
parts of the planet. Compared to Earth, Mars probably has a relatively
thick crust. Beneath the Tharsis bulge, an area of volcanic activity
in the northern hemisphere, it may be as thick as 130 km (80 mi).
Beneath the landing site of the United States spacecraft Viking 2,
it may be as thin as 15 km (9 mi). The core is probably mostly iron,
with a small amount of nickel. Other light elements, particularly
sulfur, could exist in the core as well. If so, the core may be quite
large. From studying the earth's magnetic field and core, scientists
theorize that the motions of the liquid rock in the earth's core generate
its magnetic field. Mars does not have a significant magnetic field,
so scientists believe that Mars's core is probably solid. Mars does
not, and probably did not ever, have active plate tectonics, or a
crust made up of separate sections that move about and sometimes crash
into each other. Because Mars is so much smaller than Earth, it cooled
quickly after formation and the crust thickened, forming one solid
piece and eliminating any possibility of plate tectonics as is seen
on Earth. Though the Martian crust is not broken into separate plates,
Mars's liquid mantle has sculpted the planet's surface. The molten
rock has broken through the crust to form volcanoes and its motion
has cracked the crust to form large rifts.
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THE
SURFACE OF MARS
IV
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The surface of Mars resembles a windblown desert. The two low hills in the distance may form part of a crater. Near the spacecraft itself,foreground, numerous rocks, many about 10 cm (about 4 in) across, cover the ground. |
more
carbon dioxide is frozen out in the south than the north because Mars
is farthest from the sun, and therefore coldest, in the southern winter.
Carbon dioxide may also make up the southern permanent cap. Regions
of striped-looking terrain, probably formed of layers of dust and ice,
occur at the edges of both polar caps. Climate cycles almost like the
ice ages on the earth may have caused this layering.TOP OF PAGE
THE ATMOSPHERE OF MARS
V
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On an overcast Mars morning, clouds drift through a pink skyscape. In late July 1997 the Mars Pathfinder lander returned the first pictures taken on Mars of an overcast sky. Scientists believe the Martian clouds are made up of water-ice crystals and dust. The clouds appear in the Martian sky in the early morning and dissipate as the sun warms the planet. |
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SPACECRAFT MISSIONS TO MARS
VI
The Mars Pathfinder spacecraft, launched by the United States in 1997, was made up of a lander containing weather equipment and cameras, and a small rover, which explored the surface of Mars around the lander. The lander folded up around the equipment and the rover for the journey to Mars, then unfolded when it reached the planet's surface.
Space probes have provided the most detailed information about Mars. Exploration of Mars began in 1960, when the former Union of Soviet Socialist Republics (USSR) launched its first probe to Mars. The United States National Aeronautics and Space Administration (NASA) launched the Mariner and Viking programs in the 1960s and 1970s. The programs returned vast amounts of data about the chemical and physical characteristics of Mars and a large number of photographs of its surface.
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Soviet and Russian Exploration of Mars
VII
The Soviet program to explore Mars suffered many setbacks. The USSR sent 12 probes to Mars before their first partial successes with missions Mars 4, 5, and 6 in 1973. The Soviets then waited 15 years to again explore Mars, until the Phobos missions in 1988. The Phobos probes primarily studied Mars's moon Phobos. Phobos 1 was lost on its way to Mars, but Phobos 2 sent back information on the composition of both Phobos and Mars for a limited time. Russia has continued scientific study of Mars after the dissolution of the Soviet Union, though on a more modest scale than the Soviet space program. In November 1996 the Russian spacecraft Mars 96 suffered an unsuccessful launch and crashed back to the earth. BUnited States Exploration of Mars The U.S. exploration of Mars began with the Mariner program. The spacecraft Mariner 4, launched in 1963, took the first close-up pictures of Mars. These pictures had a powerful impact because they only showed impact craters on Mars like those on Earth's moon. They did not reveal any evidence of the advanced civilizations that people in the 19th century imagined might exist on Mars. Mariners 6 and 7 took much more detailed pictures of the Martian surface and took measurements of the force of gravity and the atmosphere. Mariner 9, launched in 1971, revealed the volcanoes, canyons, and channels of Mars, showing that the planet was much more like Earth than like the moon. NASA launched another series of probes to Mars, Viking 1 and 2, in 1975.
These spacecraft provided scientists with most of the current data about Mars. The Viking probes included orbiters, which mapped Mars and made global studies of its geology and chemistry, and landers, which measured the composition of the surface and searched for life. These landers were the first probes to land successfully on Mars. Mars Observer, launched in 1992, was lost just before it reached Mars. Its near-twin, Mars Global Surveyor 96, was launched in 1996 and went into orbit around the planet in 1997. It was scheduled to reach its final orbit in early 1999, but it provided much useful data while it was adjusting its orbit. It carries instruments to measure the composition and topography of the surface and to monitor the weather conditions in much more detail than scientists can from the earth. Mars Pathfinder, also launched in 1996, consisted of a lander and a small rover. The lander studied weather conditions on Mars. The rover, called Sojourner, explored away from the lander and studied surface materials near the landing site. The Pathfinder spacecraft arrived on Mars on July 4, 1997, and operated until October 7, 1997. The lander sent back many photographs of its landing site, and Sojourner visited and analyzed 15 nearby rocks. Future missions to Mars currently under development include two spacecraft under the Mars Surveyor 98 program; both are scheduled for launch in late 1998 or early 1999. Mars Climate Orbiter will study the surface and climate of Mars, and Mars Polar Lander will land near the southern polar cap of the planet. INTERMARSNET is a program being planned by NASA and the European Space Agency (ESA) that will consist of a network of landers to study the surface and interior, complemented by an orbiter. Long-term plans for the exploration of Mars include a mission that will return samples from the planet and eventually a piloted mission.
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SEARCH FOR LIFE ON MARS
VIII
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This meteorite was probably blasted off of the surface of the planet Mars about 16 million years ago by an impact with an asteroid and travelled through space to the earth, where it landed on Antarctica about 13,000 years ago. Some scientists believe that the rod-shaped structures across the top and center of this image may be tiny fossilized bacteria. Many other scientists believe that the structures were formed by processes other than life. NASA/Science Source/Photo Researchers, Inc. |
Humans have looked for signs of life on Mars for over a hundred years. Italian astronomer Giovanni Schiaparelli and others in the middle and late 19th century believed they saw seasonal color changes that indicated a wave of greening in spring. Some people also believed that they saw canali (Italian for "channels"), or straight lines crisscrossing Mars's surface. Scientists now know that windblown dust causes the color changes and that the channels are an optical illusion. Astronomers of the early 20th century saw what they believed were more and more canals (as English-speaking observers termed them) as interest in them grew. American astronomer Percival Lowell was the most vocal proponent of these canals. He believed they indicated the existence of an advanced civilization on Mars and wrote several books on the subject in the early 20th century. He proposed that the canals carried water from the wet polar regions to the dry equatorial deserts. As telescopes improved, however, astronomers found it more and more difficult to see Lowell's canals. images of Mars's surface from the Mariner spacecraft finally proved that the canals did not exist. Lowell's beliefs about civilization on Mars have had a powerful effect on human perception of the planet. British author H. G. Wells's The War of the Worlds (1898) and American author Edgar Rice Burroughs's series of Mars books, starting with A Princess of Mars (1912), clearly show the influence of Lowell's ideas. Some people believe in the existence of a civilization on Mars even today. The so-called Face on Mars is thought by some people to be evidence of intelligent life on Mars. This feature, shown in Viking images of the Cydonia region of Mars, looks vaguely like a humanoid face. Geologists' views of these features are quite different. The Cydonia region lies near the boundary of the southern highlands and the northern plains and contains a large number of isolated hills, the eroded remnants of the edge of the highland terrain. These hills resemble the mesas of the U.S. Southwest. Their resemblance to human faces or pyramids is due to the low resolution and dark areas of missing data in the Viking images and to tricks of light and shadow. The camera on Mars Global Surveyor 96 took pictures of the region in 1998. These images revealed that the "face" was just a hill. One part of the Viking landers' mission was to search for evidence of life. One instrument was designed to detect organic molecules in the soil. It found no evidence of organic molecules. Three biological experiments tested soil samples for evidence of metabolism, growth, or photosynthesis. None of these experiments showed substantial evidence for the presence of life. Most scientists today believe that there is no life on Mars. Conditions there are extremely hostile to life as we know it. Because of the thin atmosphere, ultraviolet radiation that can destroy living matter reaches the surface. It is so cold that liquid water cannot exist on the surface during the night. If life ever had established a foothold on Mars, it would likely have affected the environment there in some way, but no evidence of this exists. However, it is not impossible that some form of life could exist on Mars today. Inside pores and cracks in rocks, where there is protection from the extreme conditions of the surface, and where liquid water can exist even at very low temperatures, it is theoretically possible that living organisms could survive. In August 1996 NASA scientists announced that a meteorite consisting of Martian rock contained possible fossil evidence of bacteria-like life. Further study of the chemical components of the rock offer little support for this theory, but the possibility that the rock contains fossils has not been eliminated. If confirmed, this discovery would be the first evidence for life outside the earth. It would increase the likelihood of life elsewhere in the universe, because it would mean that the conditions for the development of life are not specific to Earth.
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MARS MOONS
IX
DEIMOS
In Greek mythology, Deimos is one of the sons of Ares (Mars)
and Aphrodite (Venus); "deimos" is Greek for "panic".
Deimos ("DEE mos") is the smaller and outermost of Mars' two moons.
It is the smallest known moon in the solar system.
orbit: 23,459 km from Mars
diameter: 12.6 km (15 x 12.2 x 11)
mass: 1.8e15 kg
Discovered 1877 August 10 by Hall, photographed by Viking 1 in 1977.
Deimos and Phobos are composed of carbon-rich rock like C-type
asteroids and ice. Both are heavily cratered.
Deimos and Phobos are probably asteroids perturbed by Jupiter
into orbits that allowed them to be captured by Mars.
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PHOBOS
In Greek mythology, Phobos is one of the sons of Ares (Mars) and
Aphrodite (Venus). "phobos" is Greek for "fear" (the root of "phobia").
orbit: 9378 km from the center of Mars
diameter: 22.2 km (27 x 21.6 x 18.8)
mass: 1.08e16 kg
Phobos ("FOH bus") is the larger and innermost of Mars' two moons. Phobos is closer to its primary than any other moon in the solar system, less than 6000 km above the surface of Mars. It is also one of the smallest moons in the solar system.
Discovered 1877 August 12 by Hall; photographed by Mariner 9
in 1971, Viking 1 in 1977, and Phobos in 1988.
Phobos orbits Mars below the synchronous orbit radius. Thus it rises in the west, moves very rapidly across the sky and sets in the east, usually twice a day. It is so close to the surface that it cannot be seen above the horizon from all points on the surface of Mars.
And Phobos is doomed: because its orbit is below synchronous altitude tidal forces are lowering its orbit (current rate: about 1.8 meters per century). In about 50 million years it will either crash onto the surface of Mars or (more likely) break up into a ring. (This is the opposite effect to that operating to raise the orbit of the Moon.)
Phobos and Deimos may be composed of carbon-rich rock like C-type asteroids. But their densities are so low that they cannot be pure rock. They are more likely composed of a mixture of rock and ice. Both are heavily cratered. New images from Mars Global Surveyor indicate the Phobos is covered with a layer of fine dust about a meter thick, similar to the regolith on the Earth's Moon.
 |
The
Soviet spacecraft Phobos 2 detected a faint but steady outgassing
from Phobos. Unfortunately, Phobos 2 died before it could determine
the nature of the material; water is the best bet. Phobos 2 also
returned a few images (USSR IMAGE). |
The most prominent feature on Phobos is the large crater named Stickney, the maiden name of Hall's wife (above). Like Mimas' crater Herschel (on a smaller scale) the impact that created Stickney must have almost shattered Phobos. The grooves and streaks on the surface were probably also caused by the Stickney impact.
Phobos and Deimos are widely believed to be captured asteroids. There is some speculation that they originated in the outer solar system rather than in the main asteroid belt.
Phobos and Deimos may someday be useful as "space stations" from which to study Mars or as intermediate stops to and from the Martian surface; especially if the presence of ice is confirmed.
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RECOMMENED READING
X
Baugher, Joseph F. Space Age Solar System.
Wiley, 1987. One of the first post-Voyager texts.
Chapman, C. P. and Morrison, David.
Cosmic Catastrophes. Plenum, 1989.
Emphasis on asteroid collisions and other
disruptive events in solar system.
Davies, John Keith. Cosmic Impact. St. Martin's, 1986.
Meteorites, the solar system's wanderers from the asteroid belt.
Reidy, David and Wallace, Ken.
The Solar System: A Practical Guide. Paul, 1991.
Easy enough for high school, good enough for college beginners.
WEB LINKS
XI
Life On Mars ?
MORE COMING SOON
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