The Inner Planets

Ch 11.2 (p382-387)

Planets Made of Rock

• The inner planets – Mercury, Venus, Earth, Mars – are also called terrestrial planets.

• Terrestrial planets are the planets closet to the Sun, are made of rock and metal, and have solid outer layers.

Mercury

• The smallest planet• Closest to the Sun• No atmosphere

– The strength of a planet’s gravity depends on the planet’s mass. Because Mercury’s mass is so small, its gravity is not strong enough to hold onto an atmosphere

• No atmosphere = no wind– Temperatures:

• -170C on the side facing away from the Sun

• 450 C on the side facing the Sun

Mercury’s Surface

• Impact craters, depressions formed by collisions with objects from space, cover the surface of Mercury.

• There are smooth plains of solidified lava from long-ago eruptions.

• There are also high cliffs that might have formed when the planet cooled quickly

• Without an atmosphere, almost no erosion occurs on Mercury’s surface– As a result, features that formed billions of years ago have

changed very little.

Mercury’s Surface

• Like all inner planets, Mercury has a core made of iron and nickel.

• Surrounding the core is a layer called the mantle.

• The mantle is mainly made of silicon and oxygen.

• The crust is a thin, rocky layer above the mantle.• Mercury’s large core might have been formed by

a collision with a large object during Mercury’s formation.

Venus

• 2nd planet from the Sun

• About the same size as Earth

• It rotates so slowly that its period of rotation is longer than its period of revolution.– One day is longer than one year

• Venus rotates east to west, unlike most planets

Venus’s Atmosphere

• The atmosphere of Venus is about 97% carbon dioxide

• It is so dense that the atmospheric pressure on Venus is about 90 times greater than on Earth

• Venus has no water on its surface.

• It is covered by a thick layer of clouds made of acid

The Greenhouse Effect on Venus

• With an average temperature of about 460C, Venus is the hottest planet in our solar system.

• The high temperature are caused by the greenhouse effect– The greenhouse effect occurs when a planet’s

atmosphere traps solar energy and causes the surface temperature to increase.

• Without the greenhouse effect Venus would be about 450C cooler.

Venus’s Structure and Surface

• Venus’s internal structure is similar to Earth’s.

• Radar images show that more than 80% of Venus’s surface is covered by solidified lava

Concept Check

• How are the inner planets similar?

• Why is Venus hotter than Mercury?

Earth

• The third planet from the Sun

• Unlike Mercury and Venus, Earth has a moon.

Earth’s Atmosphere

• A mixture of gases and a small amount of water vapor make up most of Earth’s atmosphere

• They produce a greenhouse effect that increases Earth’s average surface temperature

• This effect and Earth’s distance from the Sun warm Earth enough for large bodies of water to exist.

• Earth’s protective atmosphere, the presence of liquid water, and the planet’s moderate temperature range support a variety of life

Earth’s Structure

• Earth has a solid inner core surrounded by a liquid outer core

• The mantle surrounds the liquid outer core.

• Above the mantle is Earth’s crust.

• It’s broken into large pieces, called plates, that constantly slide past, away from, or into each other

Mars

• 4th planet from the Sun• Half the size of Earth• Two very small and irregularly shaped

moons• Water on Mars is mainly trapped in the

polar ice caps and a small amount in found as liquid vapor

• However, little evidence of liquid water or life has been found

Mar’s Atmosphere

• 95% carbon dioxide

• Temperatures: -125C – 20C

• Dust storms that last for months

Mar’s Surface

• Reddish due to iron oxide in the soil (rust)

• Enormous canyons

• Largest mountain in the solar system

• Polar ice caps made of frozen carbon dioxide and ice