The Nine Planets
(13.14)
The Inner Planets
The four planets closest to the Sun are
Mercury, Venus, Earth, and Mars.
All four of these planets are made up of a
rocky material and therefore are called
the terrestrial planets.
These planets are also known as the inner
planets.
Mercury
Mercury is the closest planet to the Sun;
therefore, it gets sunlight that is 10
times brighter than the Earth’s.
Mercury does not have an atmosphere to
help trap the heat it receives from the
Sun, so it loses all of its heat at night
dropping to -180 degrees Celsius (oC).
Mercury’s daytime temperature is a
sweltering 400 (oC).
Mercury is rarely
seen in our
night sky
because it is so
close to the
Sun.
When we do see
Mercury, it is
generally at
sunset and at
sunrise.
Venus
After the Sun and the Moon,
Venus is the brightest object
that we can see in the sky
because it is so close to our
planet Earth.
Also, the atmosphere on Venus is
very thick and the light it
receives from the Sun is
reflected to us.
Venus’s atmosphere is made up
from mainly carbon dioxide.
This gas acts like the glass of a
greenhouse and keeps the
surface of the planet hot
enough to melt lead.
Earth
Life has grown on Earth because the
atmosphere on this planer is perfect for
beings to have changed.
Earth’s atmosphere is mainly made up of
nitrogen, oxygen, and water vapour.
There is a small amount of ozone in our
atmosphere and this is what filters
some of the damaging radiation from
the Sun.
Water from lakes, oceans,
and rivers covers
approximately 70% of
planet Earth.
The rest of the Earth’s
surface is covered by
soil, which allows for
the growth of
vegetations and habitat
for land creatures.
Earth is changing every
day because of several
environmental factors
such as volcanoes,
earthquakes, and
pollution.
Mars
Mars is one of the
brightest planets in the
sky and is sometimes
referred to as the
“RED Planet” because
of the reddish tinge it
casts. This reddish
colour is caused by the
rust-coloured soil.
Mars is very dry and
barren, but there is
evidence that Mars was
once covered with
volcanoes, glaciers and
flood waters.
The Outer Planets
The remaining 5 planets in our solar system
are known as the outer planets: Jupiter,
Saturn, Uranus, Neptune and Pluto.
The first 4 of these planets are also known
as the Gas Giants. Their atmosphere
consists mainly of hydrogen and helium.
These planets have soupy surfaces and gets
denser as you sink to the middle. Not
possible to land on.
The outermost planet, Pluto, is unique among
the outer planets.
Jupiter
Jupiter is the largest
planet of all of the
planets.
Its diameter is 11
times larger than
Earth’s diameter.
Its mass is greater
than the masses of
all the other planets
combined.
Jupiter is also a very bright object in the
night sky because of its size and the
large amount of light reflected by its
clouds.
Jupiter’s most interesting features are
its coloured bands and the Great Red
Spot.
Jupiter has approximately 16 moons, and
sometimes you can see four of these
moons by using binoculars.
Saturn
Saturn is the second-largest planet, but it is
the least dense of all the planets, with a
possibility of no core.
Saturn’s atmosphere is cloudy and windy.
Saturn’s average temperature is -180oC.
Uranus
Uranus’s diameter is 4
times larger than
Earth.
Its atmosphere is made
up primarily of
hydrogen, with some
helium and methane.
This planet has winds
that blow up to 500
km/h. In our night sky,
Uranus looks like an
extremely faint star.
Neptune
From Earth, Neptune is
barely visible with the
use of a telescope.
Neptune has bright blue
and white clouds and a
dark region – the Great
Dark Spot – that
appears to be the
centre of a storm.
Neptune has at least 8
moons and thin rings
orbiting around it.
Pluto
Pluto is now classified as a
dwarf planet. It is unusual
because it is not a gas
giant and it does not seem
to be terrestrial.
The motion of Pluto’s orbit
suggests that Pluto may
have been one of
Neptune’s moons at one
time.
Pluto also has a moon called
Charon which is about the
same size as Pluto.
Planetary Summary
Closest to
the Sun
0.386
0
Brown crater
Chunks of rock
2nd from
the Sun
0.72
0
Hot enough to
melt lead
CO2, N2
3rd from
the Sun
1
1
Soil and Water
N2, O2
0.5326
2
4th from
the Sun
5th from
the Sun
Reddish
coloured soil
none
CO2, N2
Volcanoes,
glaciers
Winds,
hurricanes
11
63
Coloured Bands,
Great Red Spot
H2, He, CH4
6th from
the Sun
10
33
Surface temp. is
About -180o
H2, He, CH4
7th from
the Sun
4
29
Polar hood over
South pole
H2, He, CH4
8th from
the Sun
3.8
13
9th from
the Sun
0.186
3
It’s blue.
Cold and rocky
59 days
To orbit Sun
A 1.7 KM high
Volcano
Volcanoes,
hurricanes
Windy,
cloudy
500 km/h
winds
H2, He, CH4
Dark spot
none
Rotates on
side
Questions – p. 428: 1, 3, 9
1.
Why are the four planets closest to the Sun
called the “terrestrial planets”?
The word terrestrial refers to Earth. Mercury,
Mars, and Venus have several properties in
common with Earth, so together the four
planets are called the terrestrial planets
3. Why is Jupiter easy to see in the night sky?
Jupiter is very large, and its atmosphere
reflects a lot of light from the light.
9. List the steps that were followed in
discovering Neptune. How do these steps
relate to the process of scientific
discovery?
Scientists observed that Uranus was a
plant; then they discovered that its motion
was not smooth. They made a hypothesis
that another object was tugging on Uranus.
They predicted where the other object was;
then they tested their hypothesis and
discovered Neptune. This process resembles
scientific discovery: observing brings more
questions followed by hypothesis,
predicting, and testing.