Chapter 29 The Solar System Section 2 Inner Planets Notes 29-2

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

Mercury

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

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

Mercury Atmosphere Temperature range Has a week magnetic field 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 week magnetic field Core may still be molten

Venus

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”

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

Venus Called Earth’s twin Only volcanically active in few hot spots 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

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

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