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Our Solar System
How our Solar System is Formed

Many First Nations and Métis peoples of Saskatchewan
understand that celestial bodies like the Sun, the stars,
and the Moon owe their origin to the Great Spirit.
Turtle Island

The story of Turtle Island and the Sky World is an example
of a creation story that explains the existence of Earth
(Turtle Island) and the heavens (Sky World). Some
Haudenosaunee of Ontario believe that the Great Spirit
(Gehi Mnidoo) fashioned both the sky and Earth. In the
story, a woman fell from the Sky World, a place that
existed like a dome over Earth. The animals of Earth, its
only inhabitants in that time, rushed to help her, but
without any land to rest upon, she would perish. The
animals tried to find land and all of them failed, except
Toad who dove deep into the ocean and brought up
dirt in his mouth. The animals spread the dirt over the
great Turtle’s back and created North America. Sky
Woman cast up a handful of dust from the land, making
the stars. Sky Woman then made the Sun and the Moon
The Solar System

Scientists describe our solar system as the Sun and all the
planets and other celestial objects, such as moons,
comets, and asteroids, that are held by the Sun’s gravity
and orbit around it.
The Nebular Theory

The most accepted scientific theory on how the solar system was
formed is called the nebular theory. A nebula is a cloud of dust and
gases in space, which scientists believe is an area of star formation. The
nebular theory explains that, after the Sun formed, the solar wind blew
against the nebula from which it formed. This pushed the gas and dust
away from the Sun. The leftover dust, gases, and other debris in the
nebula that remained continued to spin, creating a thin disk around the
new star. From within this disk, small bodies began to form, growing into
the planets, moons, asteroids, and comets that make up the solar
system. This process, astronomers believe, is how other star-and-planet
systems in the universe have formed as well.
The Sun

The Solar and Heliospheric Observatory (SOHO), a solar space
telescope, has had a clear view of the Sun since 1995.

Our Sun is of medium size by star standards and is composed mainly
of hydrogen (73 %) and helium (25 %).

The rest is made up of heavier elements including carbon, oxygen,
and iron. It formed in the same way that all stars do, taking shape
inside a nebula. The Sun is believed to have first begun shining, or
radiating energy, about 5 billion years ago and is expected to
continue shining for about 5 billion years more before it runs out of
fuel.
Measuring Distances in Space
The distances in space are so vast that astronomers
developed special units of measure.
 One unit used to measure distances in space is the
astronomical unit. One astronomical unit (AU) equals the
average distance between the Sun and Earth, or the
Diameter of Earth’s orbit, 1.49 x1011 m about 150 million
km.
 Mercury is 0.39 AU from the Sun. This value is less than 1
AU because Mercury is closer to the Sun than Earth is.
Mars is farther from the Sun than Earth is. It is 1.52 AU from
the Sun.

Measuring Distances in Space

Outside the solar system, the distance to other celestial
objects again becomes so great that even the AU is too
small to be a useful unit of measure. Instead,
astronomers usually use a unit called the light-year. One
light-year (ly) equals the distance that a beam of light
travels through space in 1 year. It is equivalent to 63 000
AU or 9000 billion km. At the speed of light, you could
travel around Earth seven times in 1 s.

Another measurement is the Parsec which is the average
distance to the edge of our galaxy = 3.26 Light Years.
Planets

After the Sun, the next largest astronomical bodies in the
solar system are the planets.

A planet is an astronomical body that orbits one or more
stars and is capable of forming into a spherical shape
under its own gravitational force, or gravity.

A planet does not create nor radiate its own energy like
a star does. It only reflects the light of the star or stars that
it orbits.
The Rocky Inner Planets

As the spinning particles of dust and gas slammed into
each other during the early stages of the solar system’s
formation, some of the particles began sticking together.

As these objects got bigger in mass, gravitational forces
caused them to contract and bind together even more
strongly. Objects orbiting too close to the Sun gradually
fell into it, drawn by its gravitational force. However, four
large objects lasted and eventually formed the four
rocky planets of the inner solar system: Mercury, Venus,
Earth, and Mars.
The Four Gas Giants

Astronomers believe that the four largest planets in the
solar system may have grown as they did because ice
acted as a kind of glue to cause gas and dust particles in
the outer regions of the solar system to stick together.

The result was the four outer planets: Jupiter, Saturn,
Uranus, and Neptune.

They are often referred to as the gas giants because their
atmospheres are made mostly of hydrogen and helium
and because they are much larger than the inner
planets.

All of the gas giants are orbited by numerous moons.
Jupiter and Saturn each have more than 60 moons
A Different Theory on Solar System
Formation

Alan Boss proposes another theory of solar system
formation. He believes the nebular theory does not
explain the formation of the planets Uranus and
Neptune. Although these planets are considered gas
giants, they both have large rock and ice cores with a
thin gas layer.

Boss’s theory states that the formation of the outer
planets was affected by another young star nearby.
According to Boss, this star was much larger than the
Sun, extremely hot, and emitted extreme UV radiation.
A Different Theory on Solar System
Formation

The Sun’s gravity created a protective zone. Jupiter
became the largest planet because it was fully
protected. Saturn is smaller because it is located
between the two star zones and had some of the
available material diverted by the competing stars away
from Saturn’s formation. Neptune and Uranus were
closer to the larger star and similarly had materials
stripped away from their formation. What was left
condensed to form those two planets. The other star
died and the Sun, along with our forming solar system,
was pushed out of the nebula and sent to a calmer part
of the galaxy
Other Objects in the Solar System

Many smaller objects exist in the solar system besides the
eight planets. These include moons, comets, dwarf
planets such as Pluto, and tiny grains of dust and ice.
The Asteroid Belt

Between the inner rocky planets and the outer gas
giants lies a huge band of billions of rocks, spread out in
a vast ring circling the Sun at a distance of about 3 AU.
The Asteroid Belt

These rocks are asteroids—metallic, rocky bodies without
atmospheres that orbit the Sun but are too small to be
classified as planets. This ring of rocky debris is known as
the asteroid belt.

Asteroids can range in size from 1000 km in diameter to
the size of pebbles. Most asteroids are less than a
kilometre in diameter.
Asteroids

Astronomers study asteroids for a number of reasons.
One of these reasons is that many celestial bodies have
hit Earth and the Moon. It is widely believed that 65
million years ago, a comet or asteroid hit Earth at three
impact sites. The impact and the effects of the impact
are believed to have caused the mass extinction of the
dinosaurs.
Asteroids

The analysis of asteroids has given us the estimated age
of the solar system. This is why asteroids are often known
as “fossils.” By the 1950s, scientists had found a way to
determine the age of many asteroid specimens. The
oldest ones were dated at 4.56 billion years old. Since
Earth would have formed at the same time as the
asteroids did, researchers have used this asteroid-dating
technique to date Earth. As it took time for the asteroids
to form, the Sun and solar system are currently estimated
to be about 5 billion years old.
Dwarf Planets

Dwarf planets are similar to planets in that they orbit the
Sun and have a roughly spherical shape, but unlike
planets, they have an unusual orbit or orbit in a zone that
contains many other objects.
The Story of Pluto

Pluto was discovered in 1930 and was known as the
smallest planet in the solar system and the ninth planet
from the sun.

Pluto is a dwarf planet.

In 2003, an astronomer saw a new object beyond Pluto
and thought he had found a new planet.

This caused other astronomers to talk about what makes
a planet a "planet." There is a group of astronomers that
names objects in space. This group decided that Pluto
was not really a planet because of its size and location in
space. So Pluto and objects like it are now called dwarf
planets.
Protoplanets

Similar to asteroids, dwarf planets are believed to have
been created when the solar system formed. Using
improved technologies, astronomers are able to gather
more data about the dwarf planets. It is believed that
the dwarf planet HL Tau b will one day become an
actual planet. Scientists refer to these dwarf planets that
are still forming as protoplanets. It will take a lot of time
for this to occur, but by recording data, the question of
how planets actually form may be answered.
Comets

A comet is a celestial object made
of ice and dust, often called a “dirty
snowball,” which travels in an
elliptical orbit around the Sun. When
a comet nears the Sun, the Sun heats
the comet, causing some of its ice
particles to break away. Carried
away from the Sun by the solar wind,
these icy particles spread out into a
tail millions of kilometres long and are
lit up by reflecting the Sun’s light.
Comets

The brightness of a comet depends on two things: how
close the comet is to the Sun, which controls the comet’s
activity, and how close the comet is to Earth.

Astronomers have been recording the appearance of
comets since 2000 BCE. Scientists believe that comets
were created from the same nebula that formed the
planets.
Comets

Some believe that the ice that surrounds comets plays
an important role in the creation of oceans and
atmospheres.

As a comet or asteroid comes close to Earth, there is the
possibility that it will fall from orbit and collide with Earth.
Astronomers have developed the Torino Scale to help
communicate the possibility of such a collision. The scale
ranges from 0 to 10, where 0 indicates little or no impact
and 10 is a collision that would cause global climatic
change.
A Deathly Collision

Evidence shows that a comet or asteroid hit Earth 65
million years ago in the Yucatán Peninsula, in Mexico.
This impact caused global tidal waves, worldwide
firestorms, dust storms, and massive earthquakes.
Scientists believe that these events caused the extinction
of the majority of species on Earth, which included the
dinosaurs.
Meteors and Meteorites

Meteoroids are small pieces of rock or metal that travel
throughout the solar system with no fixed path. They are
thought to be similar in origin to asteroids and comets.

A meteor is a meteoroid that, upon entering Earth’s
atmosphere, collides with gas molecules and the surface
material is vaporized.

Most meteors are not much bigger than a grain of sand.
If a meteor does not burn up completely and strikes
Earth’s surface, it is called a meteorite.

For the Blackfeet Nation of Montana, a meteor event
was an omen. It meant that either a great sickness
would affect the tribe that winter or that a great chief
had passed away.

A greater than usual number of meteors can be seen
during celestial events known as meteor showers.