Planets and Solar System



The Planets and the Solar System


Planets 2

" 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