A planet is a celestial body that revolves around a central star and does not
shine by its own light " (Grolier, 1992). The only planetary system that is
known to man is our solar system. It is made up of nine planets which range in
size and make-up. 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. In this paper I will discuss the planets and
how they are each unique. Mercury which is the planet that is closest to the sun
is the first planet I will discuss. Mercury is the smallest of the inner
planets. It is speculated that the heat from the sun made it impossible for the
gases present to become part of the planetary formation. The surface of Mercury
is extremely hot. It is approximately 470 degrees celsius on the surface and is
thought to be even hotter at the two " hot spots." These " hot
spots " are on opposite ends of the equator. It is the heat of the surface
that makes it impossible for Mercury to have any type of atmosphere. Mercury
orbits the sun once every 88 days and has a true rotation period of 58.6 days.
" It is the closest planet to the sun and therefore orbits faster than any
other planet " (Thompson/Turk, 542, 1993). It is said that Mercury rotates
three times for every two trips around the sun, so that during Planets 3 every
alternate perihelon passage the same face points directly at the sun. "
Geologically, the most remarkable features of Mercury are compressional cliffs
or faults, just the sort of wrinkles that might form in the crust if the
interior of the planet shrank slightly " (Morrison, 74, 1993). It is
speculated that it was the solidification of Mercury's metallic core that caused
this global shrinkage. Mercury is also " . . . enriched in metal or
depleted of rock " (Morrison, 74, 1993). It is also believed that some of
the inner core of Mercury is still in a fluid state. Scientists also believe
that Mercury's surface is made partially of silicate rock. The best way to
describe Mercury is, " . . . small, heavily cratered and airless "
(Morrison, 71, 1993). 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 " (Thompson/Turk, 542, 1993). Venus is known to most 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. Planets 4 The
atmosphere of Venus made up of 98% carbon dioxide and 2% Nitrogen. This
atmosphere also has the presence of helium, neon and argon. This is yet another
thing which makes Venus different from Earth. The surface of Venus is quite a
bit like that of the Earth. The surface has volcanoes and smooth plains. "
Much of the volcanic activity on Venus takes the form of Basaltic eruptions that
inundate large ares, much as the mare volcanism flooded the impacted basins on
the near side of the moon " (Morrison, 93, 1993). One thing that differs
from Earth is that there is no water liquid on the Venusian surface. Some of the
scientific data that follows was taken out of Cattermole's book. The mean
distance from the sun is 108.20 Km. The equatorial diameter is 12,012 Km and the
equatorial rotation is 243 days. Finally the mass of Venus is 4.87*10^24 (Cattermole,
63, 1993). Venus, although different than Earth, is still our sister planet.
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 thing that is very similar to Earth is the rotation
period. Mars rotation period is only thirty seven minutes longer than the
Earth's. This would explain why Mars has significant seasonal changes just as
Earth does. It is believed that the Planets 5 difference between winter and
summer on Mars is even greater than on Earth. Mars is extremely hard to
understand due to the effect of blurring that is caused by the two atmospheres
of Mars. Scientists do know, however, that Mars is relatively small and that
changes take place in the surface features when the seasons change. It is also
known that dust storms are prevalent and leaves the surface of Mars covered by a
red haze. Mars has a very thin atmosphere which is composed of carbon dioxide,
nitrogen, argon, water vapor and oxygen. Mars also has no 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. There are also some areas where the rock is " jumbled."
The poles of Mars are iced over and the temperature is about 160 - 170 degrees
K. Mars also has its share of volcanoes. Most of these volcanoes are shield
volcanoes. The surface is littered 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. Jupiter
is the fifth planet and is the most massive of all Planets 6 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. Jupiters density is
quite low at 1.3 g/cubic cm. The atmosphere of Jupiter contains water, ammonia,
methane and carbon. It is thought by scientists that there are three cloud
layers. The wind activity on Jupiter is quite fierce and moves in jet streams
parallel to the equator. The weather on Jupiter is still very hard for
scientists to understand. There is not enough information to truly understand
how the weather is on this planet. Jupiter is most known by the normal citizen
by the rings it has. These " rings are very diffuse. The ring particles
must generally be about as big as the wavelength of light, that is, only a few
microns " (Grolier, 1992). That is why these rings are faint or diffuse.
The rings are what Jupiter is known for. Saturn is a planet which is also known
for its rings and when viewed has a yellow or grayish color. The color is from
the gaseous atmosphere and the dust particles in that atmosphere. The atmosphere
is mostly a clear hydrogen-helium atmosphere. There are also traces of methane,
phosphine, ethane, and acetylene. This atmosphere is much different than that of
the Earth's. 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 a cold planet. It has an
equatorial diameter of 120,660 Km which Planets 7 makes it the second largest
planet in our solar system. The next planet is Uranus. The main problem
scientists have with Uranus is that, "the lack of visible surface features
means that it is difficult to measure the rotation period of Uranus
"(Hunt/Moore, 388, 1983). 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. Neptune is the last of the
gaseous planets in our solar system. Its atmosphere is much like Uranus's
because it is mostly helium and hydrogen. It also contains methane. Neptune has
a diameter of 49,500 Km and a mass 17.22 times that of the Earth. It has an
average density of 1.67 /cm^3 (Grolier, 1992). 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. The final planet, which is also the smallest, and the furthest away from
the sun is Pluto. This planet 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. Planets 8 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). Hunt, G. & Moore, P.
(1983). Atlas of the Solar System. Chicago: Rand Mc Nally & Company.
Morrison, D. (1993). Exploring Planetary Worlds. New York: Scientific American
Library. Thompson, G. & Turk, J. (1993). Earth Science and the Environment.
New York: Saunders College Publishing & Harcourt Brace College Publishers.