More Information
About the Solar
System
The lightest and simplest elements, hydrogen and
helium, are abundant in the universe. Heavier
elements, such as iron and silicon, are created by
thermonuclear reactions in the interiors of stars,
and then ejected into space by those stars.
FORMATION OF
PLANETARY
NEBULA
SUPERNOVA
EXPLOSIONS
Great clouds of
gas and dust
ejected from old
stars are
gathered into
regions from
which new stars
can be made.
This region in the
constellation of
Orion shows new
stars in nebula
from which they
were formed.
The Formation of a Solar System
A solar system begins as a gas
cloud that collapses toward the
center under the influence of
gravity.
A condensation forms at the
center, which is called a
protostar.
A flattened disk of matter
surrounds the protostar, which
begins to shine.
The Formation of a Solar System
The rising temperature from the
sun removes the gas from the
inner regions, leaving dust and
larger debris.
The planets establish dominance
in their regions of the solar
system.
After almost all of the remaining
gas, dust, and small debris has
been collected by the larger
objects, the solar system takes
on the form we recognize
today.
Other Star Systems FormingWe can look at young star
systems developing today.
The planets orbiting these
stars are formed from the
surrounding disks of gas
and dust, called
protoplanetary disks or
proplyds.
PLANET FORMATIONWithin the disk that
surrounds the protosun,
solid grains collide and
clump together into
planetesimals.
The terrestrial planets
are built up by collisions
and the accretion of
planetesimals by
gravitational attraction.
The jovian planets are
formed by gas accretion.
COMPUTER SIMULATION OF THE
FORMATION OF THE SOLAR SYSTEM
Two Basic Groups of Planets
TERRESTRIAL
Small size
Low Mass
Higher density
Mostly rock
Mercury, Venus, Earth,
Mars
JOVIAN
Large size
Massive
Low density
Mostly gas
Jupiter, Saturn,
Uranus, Neptune
Common Properties of
Planet Orbits in Our
Solar System
As viewed from above,
all of the planets orbit
the Sun in a counter-
clockwise direction.
The planets orbit in
nearly the same plane.
All planets except Pluto
have an orbital
inclination of less than
7°.
Debris in Our Solar System TodayAsteroids—rocky bodies several kilometers
across which orbit the sun—are found
mainly in the asteroid belt located between
the orbits of Mars and Jupiter
Even smaller rocky objects are called
meteoroids, and are scattered throughout
the solar system.
Billions of chunks of rock and ice
called comets are located beyond the
orbit of Neptune. Occasionally, one of
these will be pulled toward the inner
solar system and form the familiar
“tails” as it orbits close to the Sun.
Other Objects
The asteroid belt is the
circumstellar disc in the Solar
System located roughly
between the orbits of the
planets Mars and Jupiter. It is
occupied by numerous
irregularly shaped bodies
called asteroids or minor
planets.
Kuiper BeltThe Kuiper belt is
a region of the
Solar System
beyond the
planets,
extending from
the orbit of
Neptune. It is
similar to the
asteroid belt, but
it is far larger-20
times as wide and
20 to 200 times as
massive. The
Kuiper belt is
home to at least
three dwarf
planets: Pluto,
Haumea, and
Makemake.
The International
Astronomical
Union (IAU) defines
a dwarf planet as
a celestial body in
direct orbit of
the Sun that is
massive enough for
its shape to be
controlled by gravity,
but that unlike a
planet has
not cleared its
orbit of other objects.
Dwarf
Planets
A dwarf planet is an object the
size of a planet (a planetary-
mass object) that is neither
a planet nor a natural satellite.
Till 2006 there were nine planets in our solar system. Pluto was farthest planet from the sun.
In 2006, the international Astronomical Union (IAU) adopted a new definition for planets. Pluto does not fit on this definition. So it demoted to a dwarf planet.
IAU Definition of a Planet A planet is a celestial body that (a) is in
orbit around the Sun, (b) has sufficient
mass for its self-gravity to overcome rigid
body forces so that it assumes a
hydrostatic equilibrium (nearly round)
shape, and (c) has cleared the
neighborhood around its orbit.
Pluto meets only two of these criteria,
losing out on the third. In all the billions of
years it has lived there, it has not
managed to clear its neighborhood.
The Oort cloud, or Öpik–Oort cloud, is a cloud of
comets and other objects. Astronomers believe it is
way beyond the orbits of Pluto and the Kuiper belt.
The Oort cloud is believed to be the source of long-
period comets in the Solar System.
Oort cloud