1. Chapter 20 Section 3: Inner planets
Key Concepts: What characteristics do the inner planets have in common? What are the main characteristics that distinguish each of the inner planets?
Key terms: terrestrial planets, greenhouse effect

2. Earth, Mercury, Venus, and Mars
More similar to one another than to the outer planets
Dense, small, rocky surfaces
Often called “terrestrial planets”

3. Earth Three main layers – crust, mantle, core
Dense core of mostly iron and nickel
Outer core is liquid, inner is solid
Crust is the rocky surface
Mantle is a layer of hot molten rock

4. Water and atmosphere
Earth is unique in having liquid water at its surface (about 70%)
Earth has enough gravity to hold most gases which make up the atmosphere. It extends more than 100 km above the surface. Only earth has so much oxygen (about 20%). Nearly all the rest is nitrogen.

5. Mercury
Mercury is the smallest terrestrial planet and the planet closest to the sun
Not much larger than our moon and has no moons of its own
Mariner 10 – went to Mercury in the 1970s.
Showed that it has many flat plains and craters on its surface; hasn’t changed for billions of years

6. Mercury’s atmosphere Has virtually no atmosphere
High daytime temperatures cause particles to move very fast, and gravity is very weak
Temps as high as 430 degrees C, low as -170 degrees C

7. Venus
So similar to Earth in size and mass that it is sometimes called “Earth’s twin”
Venus’ density and internal structure are similar to Earth’s.
Venus takes 7.5 Earth months to revolve around the sun. Takes 8 months to rotate on its axis. Rotates east to west, unlike other planets (possibly because something smacked hard into it once)

8. Venus’ atmosphere So thick that it is always cloudy
Atmospheric weight is 90 times that of Earth
Mostly carbon dioxide
Receives more solar energy than Earth, so it is hot
Average 460 degrees C
Trapping of heat by atmosphere is called greenhouse effect

9. Exploring Venus Venera 7 – 1970 – first to land
Magellan – 1990 – carried radar – confirmed Venus is covered with rock, has volcanoes and lava flows

10. Mars Red planet due to breaking down of iron-rich rocks
Atmosphere is more than 95% carbon dioxide
Temps from -140 C to 20 C
Water – not currently found but scientists think it was once covered with water. Two polar ice caps and water vapor

11. Seasons on Mars
Mars has a tilted axis, just like Earth.