FREE ESSAY ON THE SOLAR SYSTEM

THE SOLAR SYSTEM

The Solar System consists of the Sun, the nine planets and their satellites; the comets,
asteroids, meteoroids, and interplanetary dust and gas. It is composed of two systems,
the inner solar system and the outer solar system. The inner solar system contains the
Sun, Mercury, Venus, Earth and Mars. The outer solar system contains Jupiter, Saturn,
Uranus, Neptune and Pluto.
The inner planets are relatively small and made primarily of rock and iron. The asteroids
orbit the sun in a belt beyond the orbit of Mars, tumbling and sometimes colliding with
one another. Made mostly of rock and iron, the asteroids may be the remnants of a planet
that never formed. The outer planets, with the exception of Pluto, are much larger and
made mainly of hydrogen, helium, and ice. Many astronomers believe that Pluto was and
interstellar wanderer that was captured by the Sun's gravity and was not an original part
of the solar system.
The orbits of the planets are ellipses with the sun at one focus, though all except
mercury and Pluto are very nearly circular. The orbits of the planets are all more or
less in the same plane that is called the ecliptic. The ecliptic is inclined only seven
degrees from the plane of the ecliptic with and inclination of seventeen degrees. Again
with the exception of Pluto, the planets all orbit the sun in almost the same plane.
The average distance of the earth to the sun is used as a standard for measuring
distances in the solar system and is called an astronomical unit (AU). One AU is about 93
million miles or 150 million kilometers. Mercury the planet closest to the sun is at
about 0.387 AU. Pluto is the outermost planet, and it is 39.44 AU from the sun. The
heilopause is the boundary between the solar system and interstellar space, and it is
about 100 AU from the sun. The comets, however, achieve the greatest distance from the
Sun; they have highly eccentric orbits ranging out to 50,000 AU or more.
The Sun is a regular star of intermediate size and luminosity. It is one of more than 100
billion stars in our galaxy. The Sun is by far the largest object in our solar system.
The Sun is personified in many mythologies, the Greeks called it Helios and the Romans
called it Sol. Sunlight and other radiation are produced by the conversion of hydrogen
into helium in the Sun's hot, dense interior. The Sun is, at present, about 75% hydrogen
and 25% helium by mass; everything else amounts to only 0.1%. This changes slowly over
time as the Sun converts hydrogen to helium in its core. The Sun's outer layers exhibit
different rotation, at the equator the surface rotates once every 25.4 days: near the
poles it's as much as 36 days. This weird behavior is caused by the fact that the Sun is
not a solid body like the Earth. The different rotation extends considerably down into
the interior of the Sun but the core of the Sun rotates as a solid body. The Sun's core
conditions are extreme. The pressure is 250 billion and the temperature is 15.6 million
Kelvin. At the center of the core the Sun's density is more than 150 times that of water.
The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. For
the Sun's entire steadiness, it is an extremely active star. On its surface dark sunspots
bounded by intense magnetic fields come and go in 11-year cycles. Sudden bursts of
charged particles from solar flares can cause auroras and disturb radio signals on Earth;
and a continuous stream of protons, electrons and ions leave the Sun and move out through
the solar system, spiraling with the Sun's rotation. This solar wind shapes the ion tails
of comets and leaves its traces in the lunar soil. The Sun is about 4.5 billion years
old. Since its birth it has used up about half of the hydrogen in its core. It will
continue to radiate "peacefully" for another 5 billion years or so. But eventually it
will run out of hydrogen fuel. It will then be forced into radical changes which, though
commonplace by stellar standards will result in the total destruction of the Earth and
probably the creation of a nebula.
Today there are nine major planets in the solar system. They are currently known as
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. 
The planet that is closest to the Sun is Mercury. It is about 36 million-miles from the
Sun and its period of revolution is 88 days. Mercury is surprisingly dense, apparently
because it has an unusually iron core. With only a transient atmosphere, Mercury has a
surface that still bears the record of bombardment by asteroidal bodies early in its
history. Mercury passes through phases similar to those of the moon as it completes each
revolution around the Sun. It has such a thin atmosphere that in a single day it reaches
temperatures of up to 750*F. At night, it gets as cold as -300*F. This planet can only be
seen for a short time before or after sunset. Mercury is the second smallest planet in
the solar system, having a diameter of about 3,000 miles. Its mean density can compare to
the earth. Its small mass and proximity to the Sun prevent it from having an appreciable
atmosphere. The surface of Mercury is lots like that of the moon.
Venus is the second planet from the Sun. It is often called the Evening Star or Morning
Star, and it is brighter than any object in the sky except the Sun and the moon. Venus
can really never be seen much longer than 3 hrs. before or after sunrise. Venus revolves
around the Sun at a distance of about 67 million miles. Venus is often referred to as the
sister planet of the Earth because it is only slightly smaller in size and mass. Venus is
covered with a thick blanket of clouds that hides its surface from view. The thick
atmosphere is composed mainly of carbon dioxide, with a slight amount of water vapor and
some nitrogen and their elements. The high surface temperature is assumed to result
partly from the greenhouse effect because it is blocked out by the top layer. Venus
rotates on its axis in a retrograde direction with a period of about 243 days. As a
result of the Greenhouse effect Venus is the hottest of any planet about 477*C. Venus
lies between the orbit of the Sun and Earth, so Venus passes through phases like the
moon, varying from a large bright crescent (when it is close) to a silvery disk (when it
is far away). Venus comes closer to the Earth than any other planet. The surface of Venus
is thought to be erratic and stormy, but radio waves indicate the possibilities of two
long mountain ranges. Scientists have estimated that the surface of Venus is only about
800 million years old.
Earth is the fifth largest planet and the only planet definitely known to support life.
Due to gravitational forces the earth is molded into a sphere. However, the earth is not
an exact sphere, being slightly flattened at the poles and bulging at the equator. The
earth's surface is divided into dry lands and oceans. Surrounding the earth is an
envelope of gases called the atmosphere, which is mostly made of nitrogen and oxygen. The
Earth is divided into several layers which have distinct chemical and seismic properties.
The crust varies considerably in thickness; it is thinner under the oceans, and thicker
under the continents. The inner core and crust are solid; the outer core and mantle
layers are plastic or semi-fluid. Most of the mass of the Earth is in the mantle, the
rest is in the core, and the part we inhabit is a tiny fraction of the whole. Unlike the
other planets, Earth's crust is divided into several separate solid plates, which float
around independently on top of the hot mantle below. The Earth is 4.5 to 4.6 billion
years old, but the oldest known rocks are about 4 billion years. Rocks older than 3
billion years are rare. The surface of the Earth is made up of 71% water.
Mars is known as the "Red Planet", because of its striking red appearance. The planet has
a very thin atmosphere consisting mainly of carbon dioxide, with some nitrogen and argon.
The average distance of Mars from the Sun is about 141 million miles. Mars has an extreme
day-to-night temperature range, resulting from its thin atmosphere. Strong evidence
exists that Mars once had liquid water on its surface, but now its carbon dioxide
atmosphere is so thin that the planet is dry and cold, with polar caps of frozen water
and solid carbon dioxide, or dry ice.
Jupiter is the first of the "Gas Giants", and the fifth planet from the Sun. Its "Great
Red Spot" is its most well known feature. If Jupiter was hollow, you could fit over 1,000
earths inside it. Jupiter's orbit lies beyond the "asteroid" belt at a average distance
of 483.6 million miles from the Sun. Jupiter is the first planet of the outer planets.
The atmosphere of Jupiter is composed mainly of hydrogen, helium, methane, and ammonia.
The atmosphere appears to be divided into a number of light and dark bands parallel to
its equator and shows a range of complex features, including a storm called the Great Red
Spot. Located in the Southern Hemisphere the storm rotates counterclockwise and has been
observed ever since 1664. Also in the Southern Hemisphere are three white ovals that
formed in 1939. According to Scientists Jupiter has no solid rock surface. Jupiter
radiates about four times as much heat energy as it receives from the sun, implying an
internal heat source. The temperature on Jupiter ranges from about 190*F to 9*F. Its
magnetosphere, rings and satellites make it a planetary system unto itself. One of
Jupiter's largest moons, Io, has volcanoes that produce the hottest surface temperature
in the Solar System. At least four of Jupiter's moons have atmospheres, and at least
three show evidence that they contain liquid or partially-frozen water.
Saturn is the sixth planet from the Sun. It is also the second largest in mass, but has
the largest equatorial distance. Winds on Saturn can reach up to 1,100 miles per hour.
Saturn is less dense than water by 30%. Saturn's orbit lies between those of Jupiter and
Uranus, its average distance from the Sun is about 886 million miles, almost twice that
of Jupiter. Saturn appears in the sky as a yellow, starlike object of the first
magnitude. When viewed through a telescope, it is seen as a golden sphere, crossed by a
series of lightly colored bands parallel to the equator. Saturn is covered with a thick
atmosphere composed mainly of hydrogen and helium, with some methane and ammonia. Its
temperature is believed to be about 270*F. Saturn rivals Jupiter, with a much more
intricate ring structure and more satellites. One of Saturn's moons, Titan, has an
atmosphere thicker than that of any other satellite in the solar system.
Uranus is the seventh planet from the Sun, and it is the largest. Uranus is titled to the
side. It spins north-south instead of east-west. It's many rings go around the north and
south poles instead of around the equator. Uranus has a diameter roughly four times that
of Earth. Through a telescope, Uranus appears as a greenish disk, slightly elliptical
because of its rapid rotation. The temperature is estimated to be about -330*F. Uranus
has twenty known natural satellites with a diameter ranging in size from 986 miles down
to 14 miles.
Neptune is the outer most of the "Gas Giants". Its orbit is 165 Earth years. Methane
gases give Neptune its blue/green color. It has a Great Dark Spot, much like Jupiter. The
average distance from Neptune to the Sun is about 2.8 billion miles. Neptune has a thick
atmosphere along with the other outer planets. It has about the same temperature as
Uranus.
Pluto is the farthest from the Sun, but because of its eccentricity in orbit, it is
closer that Neptune's 20 years of its 249 year orbit. Pluto is mostly ice and rock.
Pluto's diameter is about 12,200 miles. Pluto and Charon (moon) are unique in that they
both keep the same side facing one another at all time because they rotate synchronously
as Chiron orbits Pluto.
The asteroids are small rocky bodies that move in orbits primarily between the orbits of
Mars and Jupiter. Numbering in thousands, asteroids range in size from Ceres, to
microscopic grains. Some asteroids are perturbed, or pulled by forces other than their
attraction to the Sun, into eccentric orbits that can bring them closer to the Sun. If
the orbits of such bodies intersect that of Earth, they are meteors and recovered
fragments are termed meteorites. Laboratory studies of meteorites have revealed much
information about primitive conditions in our solar system. The surfaces of Mercury,
Mars, and several satellites of the planets show the effects of an intense bombardment by
asteroidal objects early in the history of the solar system. On Earth that record has
eroded away, except for a few recently found impact craters.
Some meteors and interplanetary dust may also come from comets, which are basically
aggregates of dust and frozen gases. Comets orbit the Sun at distances so great that
stars enter orbits that bring them into the inner solar system can perturb them. As
comets approach the Sun, they released their dust and gases to form as spectacular coma
and tail.
The planet is a very broad term to discuss because there are so many different parts that
you can explore. The solar system is huge and just imagine what would happen if we found
another solar system! The inner planets are Mercury, Venus, Earth and Mars. The outer
planets are Jupiter, Saturn, Uranus, Neptune and Pluto. There is a big difference between
the two different groups.