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

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

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

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.

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

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

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)

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

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

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

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