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

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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