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The Solar System
Overview of the Solar System
Basics
Source: Nine Planets - A Multimedia Tour of the Solar System
* By Bill Arnett
The solar system
consists of the Sun,
the nine planets,
about 90 satellites of the planets,
a large number of small bodies (the
comets and asteroids),
and the interplanetary medium.
The nine planets are
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
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 (called the
ecliptic and defined by the plane of
the Earth's orbit).
How do they orbit?
They all orbit in the same direction
(counter-clockwise looking down
from above the Sun's north pole);
all but Venus, Uranus and Pluto
also rotate in that same sense.
The Nine Planets
Classification
Traditionally, the solar system has been
divided into planets (the big bodies
orbiting the Sun),
their satellites (a.k.a. moons, variously
sized objects orbiting the planets),
asteroids (small dense objects orbiting
the Sun) and comets (small icy objects
with highly eccentric orbits).
The Big Questions
What is the origin of the solar system? It
is generally agreed that it condensed
from a nebula of dust and gas. But the
details are far from clear.
Big questions, continued
What conditions allow the formation of
terrestrial planets? It seems unlikely
that the Earth is totally unique, but we
still have no direct evidence one way or
the other.
Big questions, continued
 Is there life elsewhere in the solar
system? If not, why is Earth special?
 Is there life beyond the solar system?
Intelligent life?
 Is life a rare and unusual or even
unique event in the evolution of the
universe or is it adaptable, widespread
and common?
The Earth
Earth
is the third planet from the Sun and the
fifth largest.
orbit:
149,600,000 km
(1.00 AU) from Sun
diameter: 12,756.3 km
mass:
5.972e24 kg
The Earth is divided
into several layers which have distinct
chemical and seismic properties
Earth’s division
(depths in km):
0- 40
40- 400
400- 650
650-2700
2700-2890
2890-5150
5150-6378
Crust
Upper mantle
Transition region
Lower mantle
D'' layer
Outer core
Inner core
The crust
varies considerably in thickness;
it is thinner under the oceans,
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,
most of the rest in the core;
the part we inhabit is a tiny
fraction of the whole
Parts of earth
(values below x10^24 kilograms):
atmosphere
= 0.0000051
oceans
= 0.0014
crust
= 0.026
mantle
= 4.043
outer core
= 1.835
inner core
= 0.09675
71% of the Earth's surface
is covered with water.
Earth is the only planet on which water
can exist in liquid form on the surface.
Liquid water is essential
for life as we know it.
The heat capacity of the oceans is also
very important in keeping the Earth's
temperature relatively stable.
Liquid water
is also responsible for most of the erosion
and weathering of the Earth's
continents, a process unique in the
solar system today (though it may have
occurred on Mars in the past).
The Earth's atmosphere
is 77% nitrogen, 21% oxygen, with
traces of argon, carbon dioxide and
water.
The tiny amount of
carbon dioxide resident in the atmosphere
at any time is extremely important to
the maintenance of the Earth's surface
temperature via the greenhouse effect.
The greenhouse effect
raises the average surface temperature
about 35 degrees C above what it
would otherwise be (from a frigid -21 C
to a comfortable +14 C);
without it the oceans would freeze and
life as we know it would be impossible.
The Moon
The Moon
is the only natural satellite of Earth:
orbit:
384,400 km from Earth
diameter: 3476 km
mass:
7.35e22 kg
The moon
is the second brightest object in the sky
after the Sun. As the Moon orbits
around the Earth once per month, the
angle between the Earth, the Moon and
the Sun changes; we see this as the
cycle of the Moon's phases. The time
between successive new moons is 29.5
days (709 hours)
The Moon was first visited
by the Soviet spacecraft Luna 2 in 1959.
It is the only extraterrestrial body to
have been visited by humans.
The first landing was on July 20, 1969;
the last was in December 1972.
The Moon is also the only body from
which samples have been returned to
Earth.
The gravitational forces
between the Earth and the Moon cause
some interesting effects. The most
obvious is the tides.
The Moon's gravitational
attraction
is stronger on the side of the Earth
nearest to the Moon and weaker on the
opposite side.
Since the Earth, and particularly the
oceans, is not perfectly rigid it is
stretched out along the line toward the
Moon.
The Moon has
no atmosphere. But evidence from
suggested that there may be water ice
in some deep craters near the Moon's
south pole which are permanently
shaded. There is apparently ice at the
north pole as well.
A piece of the moon
The End