Download - Chapter 11.2: The Inner Planets
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