The earth is only one small planet in an extremely large system of planets,
satellites, asteroids, meteors and comets that revolve around the sun. This
system is referred to as the solar system. A planet is defined as a “celestial
body that revolves around a central star and does not shine by its own light
" (Grolier,1992). The only planetary system known to our civilization is
our solar system. It is made up of nine planets that differ greatly size and
physical characteristics. The nine major planets in our solar system are
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. There
are also many other minor planets which are also in our solar system, but they
are unimportant compared to the nine major planets. Following are descriptions
of the differences that each of the nine planets have. The first planet to be
discussed is Mercury. Mercury is the planet that is closest to the sun at an
average distance of about 58 million km, or about 36 million miles. It takes
58.7 days for Mercury to rotate. The planet rotates one and one half times
during each revolution. Mercury has a density and composition close to that of
Earth and, like Earth has a magnetic field. This magnetic field is produced from
the planet’s outer core, which is said to be liquid iron. This liquid iron
generates a magnetic field with its movement. The atmosphere is extremely thin
and contains sodium and potassium. The photographs that have been taken of
Mercury's surface show the planet having craters and steep cliffs. The
temperatures on Mercury reach amazingly high levels of about 430° C, which is
about 810° F on the side facing the sun and about -180° C, or about 290° F on
the side facing away from the sun. It is speculated that these high
temperatures, resulting from the planet’s proximity to the sun made it
impossible for the gases present to become part of the planetary formation or
for Mercury to have any type of atmosphere. Venus is the second closest planet
to the sun and is said to most closely resemble Earth in size, density, and
distance from the sun. Venus is known as the sister planet to the Earth. One
differences is that Venus is shrouded in thick clouds that completely hide the
surface of the planet. The surface temperature is also much warmer than that of
Earth. Venus completes one revolution around the sun in 224.7 days. This makes
the a day on Venus equal to 117 earth days. It is thought that this slow
rotation may be the reason why Venus has no magnetic field. The atmosphere of
Venus made up of 98% carbon dioxide and 2% Nitrogen. This atmosphere also has
the presence of helium, neon, and argon. The surface of Venus is quite a bit
like that of the Earth. Cloud particles on Venus are mostly concentrated
sulfuric acid. Water and water vapor are very uncommon on Venus. Many scientists
hold the opinion that Venus, being close to the sun, was subjected to a kind of
extreme greenhouse effect. This effect caused any oceans to evaporate into the
atmosphere. Another viewpoint that is held is that Venus had very little water
to begin with. The surface has volcanoes and smooth plains. Much of the volcanic
activity on Venus takes the form of Basaltic eruptions that inundate large
areas, much as the mare volcanism flooded the impacted basins on the near side
of the moon. Because of the distances of the orbits of Venus and Earth from the
sun, Venus can never be seen for than three hours before sunrise or three hours
after sunset. When Venus is viewed through a telescope, it shows phases like the
moon. Venus rotates very slowly on its axis, in a direction that is opposite to
that of Earth. Cloud particles on Venus are mostly concentrated sulfuric acid.
Water and water vapor are very uncommon on Venus. Many scientists hold the
opinion that Venus, being close to the sun, was subjected to a kind of extreme
greenhouse effect. This effect caused any oceans to evaporate into the
atmosphere. Another viewpoint that is held is that Venus had very little water
to begin with. Higher-level winds circle the entire planet at 360 km/hr., or 225
mph. However, even with these high velocity winds, near the planet’s surface
more than half of Venus's tremendously dense atmosphere is practically still.
From the surface up to 10 km, or 6 mi. altitude, wind speeds are only about 3 to
18 km/hr, or about 2 to 11 mph. In the upper atmosphere, the night side of Venus
is extremely cold. Day-side temperatures are 40° C, or 104° F but night-side
temperatures are -170° C, or 274° F. Scientists theorize that strong winds
blow from the day side toward the near vacuum that is caused by the low
temperatures on the night-side. Venus has huge active volcanoes, large
solidified lava flows, and a vast number of meteorite craters. The composition
of Venus's dense atmosphere apparently prevents smaller meteorites from crashing
into the surface of the planet. A great deal of tectonic activity has taken
place on Venus, at least in the past. Venus is the second closest planet to the
sun and is said to " . . . most closely resemble Earth in size, density,
and distance from the sun ". Venus is often referred to by scientists as
the sister planet to the Earth. It is called this because it closely resembles
the Earth's mass, density and diameter. The only thing different is that Venus
" is shrouded in thick clouds that completely hide the surface of the
planet " (Grolier, 1992). The surface temperature is also much warmer than
that of Earth. Venus completes one revolution around the sun in 224.7 days. This
makes the Venusian day equal to 117 earth days. It is thought that this slow
rotation may be the reason why Venus has no magnetic field. Mars is the fourth
furthest away from the sun and is recognized by its reddish color. Mars is also
very much like the Earth. " More than any other planet in the solar system,
Mars has characteristics that make it an Earth-like world "(Grolier, 1992).
One similarity that Mars shares with Earth is the rotation period. Mars’
rotation period is only thirty-seven minutes longer than Earth's. This explains
the seasonal change similarity that Mars shares with Earth. It is said that the
differences between winter and summer on Mars is more extreme than that on
Earth. Mars is extremely hard to analyze and study due blurred effect that is a
direct result of the two atmospheres of Mars. Scientists have been able to
discover that Mars is fairly small and that changes take place in the surface
features upon seasonal changes. The red haze that covers Mars is a result of
dust storms. The thin atmosphere of Mars is composed of carbon dioxide,
nitrogen, argon, water vapor and oxygen. Mars is only one of the planets that
does not have a magnetic field. " Because the atmosphere of mars is so
thin, wind velocities up to several hundred Km per hour are required to raise
the dust particles during a dust storm, and these fast-moving particles erode
structures with a sand-blasting effect " (Grolier, 1992). Therefore, the
surface is basically plain-like and covered with large craters. The poles of
Mars are iced over and the temperature is about 160 - 170 degrees. Mars shares
the volcano characteristic with Venus. The surface is covered with winding
channels that resemble river channels that have dried up over time. Scientists
believe that water once existed and caused the formation of these channels. It
is said that, " Mars remains the best candidate for life in the solar
system outside of the Earth," and that is what makes Mars so interesting to
scientists, and what compels them to gain access to its surface as they once did
the moon. Jupiter is the fifth planet and is the most massive of all the planets
in this solar system. " Its mass represents more than two-thirds of the
total mass of all the planets, or 318 times the mass of the Earth. Jupiter's
magnetic field is 14 times stronger than Earth's. This magnetic field is
responsible for the huge belts of trapped charged particles that circle the
planet out to a distance of 10 million km. The atmosphere of Jupiter is made up
of water, ammonia, methane and carbon. Scientists feel that there are three
different layers of clouds. The wind activity on Jupiter is volatile, and moves
in jet streams parallel to the equator. The weather on Jupiter is still very
hard for scientists to understand. There has not been nearly enough information
compiled about conditions on Jupiter to truly understand, or describe the nature
of the weather is on this planet. Its weather conditions remain something of a
mystery, or puzzle, to scientists. One feature of Jupiter that is recognizable
by most individuals is its rings. These rings are very diffused and unclear. The
ring particles are extremely small, approximately a few microns. The size of the
particles explains why the rings are not more clearly visible. Sixteen
satellites of Jupiter have been seen so far. Io and Europa, which are close to
Jupiter, are dense and rocky. Ganymede and Callisto, at greater distances, are
mostly water ice at low densities. Callisto is almost as big as Mercury, and
Ganymede is bigger than Mercury. The surface of Europa is covered by a layer of
water ice, and a layer of liquid water may lie beneath the ice. Europa also has
a thin oxygen atmosphere. Io has volcanoes, powered by tides created in this
satellite's interior by Jupiter's gravitational force, that release hydrogen
sulfide and other sulfur compounds, giving it a mottled yellow, brown, and white
surface. The remaining moons are very much smaller. Between Jupiter and Io are
the moons Metis, Adrastea, Amalthea, and Thebe. Outside Callisto are Leda,
Himalia, Lysithea, Elara, Ananke, Carma, Pasiphae, and Sinope. Saturn is the
second largest planet and is sixth in its distance from the sun. Saturn is
famous for its rings, which first seen in 1610 by Italian scientist Galileo and
identified as rings by Dutch astronomer Christiaan Huygens in 1655. These
“famous” rings contain more than 100,000 individual ringlets. The visible
rings stretch out to a distance of 136,200 km from Saturn's center, but in many
areas they may be only 5 m thick. They are thought to contain rocks, frozen
gases, and water ice in lumps of various sizes from extremely small to large.
One of Saturn’s rings is dense enough to block sunlight. The atmosphere of
Saturn is predominantly made up of a clear hydrogen-helium atmosphere. Methane,
phosphine, ethane, and acetylene are also identifiable in smaller amounts.
Saturn orbits the sun with a period of 29.4577 tropical years. It is 1.427
billion Km away from the sun and is therefore an extremely cold planet. However,
the gravitational situation of Saturn causes it to emit three times as much heat
as it receives from the sun. Uranus is the seventh planet from the sun, and is
located between Saturn and Neptune. Uranus was discovered in 1781 by the British
astronomer Sir William Herschel and was originally named Georgium Sidus, or the
Star of George, in honor of King George III of Great Britain. The name Uranus,
proposed by German astronomer Johann Elert Bode, was in use by the late 19th
century. Uranus has a diameter of 51,120 km, and its average distance from the
sun is 2.87 billion km. It has a mass greater than Earth's. Uranus orbits the
sun once every 84 years and rotates on its axis in 17 hours 15 minutes. Its
atmosphere is mostly hydrogen and helium, with a trace of methane. Through a
telescope it appears as a blue-green disk with a faint green rim. Nine rings
orbit Uranus, which also has 15 satellites revolving around its equator. The
largest moons are named Oberon, Titania, Umbriel, Ariel, and Miranda. Even
though there have been estimates made, the main problem scientists have with
Uranus is that this planet does not have visible surface features, which means
that it is difficult to measure the rotation period of Uranus because they are
not sure which part of the planet they are viewing. Uranus has an equatorial
diameter of 51,000 Km which is almost four times as much as Earth. The
atmosphere is mostly methane gas and therefore the planet has a red tint or a
blueish green color. Uranus also has rings but unlike Saturn these rings have
almost no small particles. Scientists are not as concerned with this planet, and
have not determined that there are any significant scientific findings to be
made on its surface. Neptune is the last of the gaseous planets in our solar
system. Neptune is the fourth largest planet in the solar system, and eighth in
its distance from the sun. Its atmosphere is much like Uranus's because it
contains predominantly helium and hydrogen. It also contains methane which gives
it its blue color. Neptune has a diameter of 49,500 Km and a mass 17 times
greater than that of the Earth. Neptune is about 4.5 billion km from the sun. It
is about 49,400 km in diameter, almost 4 times as wide as Earth. Neptune’s
deep atmosphere surrounds a liquid surface and a solid core. Neptune rotates on
its axis every 16 hours and orbits the sun in 164.79 Earth years. Because of the
lack of light on the planet It cannot be seen with the naked eye, but rather
requires the usage of a telescope. Neptune has five thin rings and eight known
satellites. The largest is of the satellites is Triton, with a diameter of 2705
km, which is only slightly smaller than Earth's moon. Triton has a nitrogen
atmosphere, with some methane, and an active planetary surface with geysers. The
satellite Nereid has a diameter of about 320km. Neptune also has rings like its
other gaseous partners, but they are very faint. Not a great deal is known about
Neptune. It is widely studied by scientists and that makes it an important
planet. Pluto, the last planet to be discussed, is the smallest of the planets
and the farthest from the son. This planet, like Neptune, is not extremely
visibly, and cannot be studied extensively. Pluto is made of much rockier
material than are the other planets of the outer solar system. Many astronomers
think Pluto may be a former satellite of Neptune, which was possibly knocked
into a separate orbit during the early days of the solar system. is very hard to
see therefore not a lot is known about its physical characteristics. Scientists
do know that it has a thin methane atmosphere. Little is known about this planet
because it is so far away from the Earth and the sun. Scientists are always
learning new things and more data will arise in the future. As one can see the
planets of most importance are the ones closest to the sun and Earth. Little is
known about the far off planets therefore it is hard to give them full
recognition. Much is known about Mercury, Venus, Earth, Mars, Jupiter and
Saturn. The other three planets are not as well known as these six are. Whether
more planetary systems exist doesn't really matter. There are still plenty of
things we don't understand about our own solar system. Scientists will have
their work cut out for them in the future. Each and every planet has distinct
differences and that helps show us how truly great God is. The planets will
never fully be understood and will always be a great topic of discussion.

Bibliography
Cattermole, P. (1995). Earth and Other Planets. New York: Oxford University
Press. Grolier Electronic Publishing, Inc. (1992).