The Inner Planets

Chapter 27 - 3

Terrestrial Planets

• Mercury, Venus, Earth, Mars• Mostly solid rock with metallic cores• Impact craters

Mercury

Mercury

• Revolution – 88 days• Rotation – 59 days• Day – 427°C due to no atmosphere and slow

rotation• Night - ¯173°C

Venus

Venus

• Revolution – 225 days• Rotation – 243 days• Similar size, mass, and density to Earth• Atmosphere about 96% carbon dioxide which

causes runaway greenhouse effect• Hottest planet with average temperature 464°C• Sulfur dioxide droplets form cloud layer that

reflects sunlight• Called the evening star or morning star

Missions to Venus

• 1970s, Soviet Union sent 6 probes• Showed basalt and granite rocks (similar to

Earth) • 1990s, US sent Magellan satellite to orbit

which sent back info about atmosphere and surface

Venus’ Surface Features

• Mountains, volcanoes, lava plains, sand dunes• Maat Mons – highest volcano• Heat within the planet causes volcanoes to

erupt• Craters are same age, young

Earth

• Intense geologic history – tectonic plates, weathering, erosion

• Unique atmosphere and distance from sun allow water to be in liquid form

• Oceans absorb carbon dioxide

Mars

Mars

• 228 million km from sun• Revolution – 687 days• Rotation – 24 h 37 min• Seasons like Earth’s seasons• Geologic activity in the past• Valles Marineris – canyons as long as the US is wide• Olympus Mons – 24 km tall volcano (may have had a

magma source for millions of years)• Viking indicated marsquakes which may show activity

Water on Mars

• Pressure and temp too low for liquid• 20°C in summer and ¯130°C in winters• Water is in ice caps at poles• Water may be found beneath the surface

The Outer Planets

Section 27-4

The Gas Giants

• Jupiter, Saturn, Uranus, Neptune• Separated from the terrestrial planets by an

asteroid belt• Large, made mostly of gas• Less dense than terrestrial planets• Strong gravity held onto original atmospheres (H

and He at top layer)• Probably core of rock and metals• All have rings of dust and ice

Jupiter

Jupiter

• 300 x the mass of Earth• Revolution – 12 years• Rotation – 9 h 50 min (fastest)• At least 60 moons

Jupiter’s Atmosphere

• 92% H and He (same as sun but not enough mass for nuclear fusion to begin)

• Rapid rotation causes different colored bands to form (organic molecules mixed with ammonia, methane and water vapor)

• Average temp ¯160°C

Jupiter’s Weather and Storms

• Great Red Spot – similar to hurricane, hundreds of years old

• Galileo measured wind speeds of 540km/h

Jupiter’s Interior

• Large mass causes temp and pressure to be great

• Inner layers are liquid Hydrogen which may contain electric currents giving Jupiter its magnetic field

• Rocky, iron core maybe

Saturn

Saturn• Revolution – 29.5 years• Rotation – 10 h 30 min• Average temperature is ¯176°C• Also made of mostly H and He• At least 30 moons• Titan is half the size of Earth• Extensive ring system (particles from comets and other

rocky bodies)• Bulges at equator because of spinning and low density• Cassini-Huygens launched in 1997 and landed in 2004

sent info about Saturn and Titan

Uranus

Uranus

• Revolution – 84 years• Rotation – 17 h (horizontally)• Information from Hubble Space Telescope and

Voyager 2• Atmosphere of H and He• Blue-green due to methane• Average temp ¯214°C• Solid rock and metal core maybe• Maybe liquid water under clouds

Neptune

Neptune• Revolution – 164 years• Rotation – 16 h• At least 8 moons• Uranus’s orbital period was showing variations,

so it was thought that another planet’s gravity was pulling on it.

• Atmosphere mainly made of H, He, methane• Strongest winds • Great Dark Spot (Earth-sized storm)• Average temp is ¯225°C

Nonplanets

• Pluto– Frozen methane, rock, and ice– Average temp of ¯235°C– Charon is the only moon

• Kuiper belt• Sedna• Exoplanets– Planets that orbit stars other than the sun– Seen by their gravitational pull on the stars they orbit