Chapter 3 The Solar System

1. Chapter 3The Solar System Section 2 Inner Planets Notes 3-2

3. Inner Planets • Terrestrial Planets: • Similar to Earth • Solid rock with a metal core • No rings • Number of moons varies from 2 to zero • Covered with impact craters • From collisions with rocky pieces during the later stages of formation

4. Mercury

5. Mercury • Closest to the sun • Named after Roman god Mercurius • Swift messenger of the gods • Short orbital period = 88 Earth days • One rotation = 59 Earth days • Rotates 3 times in 2 orbits • Speed is about 50 km/s • No moons

6. Mercury • Mariner 10 (1974 and 1979) • Visited Mercury • Surface covered with craters • Craters appear to have hardened lava inside • Mercury was once volcanic • Has changed very little since it was first formed • Hard to see because of proximity to the sun • Sometimes can be seen on horizon at sunrise or sunset

7. Mercury • Atmosphere • Very thin • Constantly being blown away by solar winds • Gravity is weak and can’t hold gases in • Temperature range • High = 427 °C (during the day) • Low = -173 °C (during the night) • Has a weak magnetic field • Core may still be molten

8. Venus

9. Venus • Second planet closest to the sun • Named after Venus, Roman goddess of beauty and love • One of the brightest objects in the sky • Third only to the sun and the moon • Known as the “morning star” or “evening star”

10. Venus • Orbital Period = 225 Earth days • Rotates slowly = 243 Earth days • Rotates in the opposite direction than the other planets • From east to west • No moons • Average surface temperature = 464 °C • Atmospheric pressure = 90 x Earth’s

11. Venus • Called Earth’s twin • Almost the same in size, mass and density • 95% of Earth’s diameter • 80% of Earth’s mass • Only volcanically active in few hot spots • Large shield volcano called Sif Mons • Carbon dioxide from volcanoes was trapped in the atmosphere

12. Venus • Atmosphere • 96% carbon dioxide • Allows infrared in but traps it on the surface • Run away Greenhouse Effect • Water boiled off because of high temps • Clouds contain sulfuric acid • Rains sulfuric acid

13. Venus • Soviet Union set 6 probes in the 70’s • survived heat, pressure and sulfuric acid long enough to send pictures back • Surface is smooth with some mountains and valleys • Composed mostly of basalt and granite • Magellan orbiter (‘90 & ‘92) • Used radar to see surface • Most common are domes, mountains, volcanoes and lava plains