Section 3-1 (Part 2)
Inner Planets
Objectives
•
Define period of rotation
•
Define period of revolution
•
Identify the characteristics of Mercury,
Venus, Earth and Mars
Period of Rotation
•
The time it takes for
a celestial body to
spin or rotate once
•
Earth’s period of
rotation is 24 hours
or 1 day.
Period of Revolution
•
Time it takes for a
celestial body to
revolve around the
Sun once
•
Earth’s period of
revolution is
365.242 days
Mercury
Mercury
•
Closest planet to the Sun
–
3.2 light-minutes from the
Sun
•
Doesn’t have an
atmosphere like Earth
does
•
Period of rotation = about
59 days
–
1 day on Mercury is equal to
59 days on Earth
•
Period of revolution = 88
days
Mercury
•
Gravity on Mercury
is only
38%
of the
Earth’s gravity
Size of Mercury vs. Size of Earth
Venus
Venus: Earth’s Twin?
•
Second-closest planet
to the Sun
–
6 light-minutes from
Sun
•
Has the hottest
surface temperature
of
any
planet.
•
Why doesn’t Mercury
have the hottest
surface?
Venus
•
Venus has an
atmosphere that is
even thicker than
Earth’s
–
Made up mostly of
carbon dioxide
–
Atmosphere keeps
the heat in (traps
heat)
Venus
•
Period of Rotation =
243 days BUT it
spins in opposite
direction
–
Earth spins
Counterclockwise
(
Prograde rotation
)
–
Venus spins
clockwise
(
Retrograde
rotation
)
Venus
•
Gravity is 91% of
Earth’s gravity
Size of Venus vs. Size of Earth
Earth
•
Why is Earth able to
support life, but
Venus and Mars are
not?
Earth
•
The Earth is at just
the right distance
from the Sun
–
Any closer and our
oceans would boil
away
–
Any further and
oceans would be all
ice
•
Water is the key to
life
Earth
•
3rd planet from the
Sun
–
8.3 light-minutes
from Sun
•
Period of rotation =
24 hours (1 day)
•
Period of revolution
= 365.242 days
Mars
Mars
•
4th planet from the
Sun
–
12.7 light-minutes from
Sun
•
Because of thin
atmosphere and
distance from Sun,
Mars is very cold
Mars
•
Period of rotation =
about 25 hours
–
Very similar to
Earth’s
•
Period of revolution
= about 2 years
•
Gravity is 38% of
Earth’s gravity
Mars
•
Mars is the
most studied
planet, other
than Earth
Rover studying a rock on Mars
Water on Mars?
•
Atmosphere is too
thin
–
Not enough pressure
to keep water in
liquid form
–
Any water would
evaporate
•
Mars has ice,
though.
Mountains on Mars
•
Olympus Mons
:
largest
mountain/volcano in
the entire Solar
System
Mercury,Venus,Earth,Mars
What is common between
Mercury, Venus, Earth and
Mars?
Terrestrial Planets
•
Similar to Earth
–
Small, dense and
made of rock
•
Also called Inner
Planets
•
Include Mercury,
Venus, Earth and
Mars