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