Planetary Physics

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