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Chapter 13 The Solar System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. “Give thanks to the Lord, for he is good. … who made the great lights – the sun to govern the day, the moon and stars to govern the night; …” Psalms 136:1, 7-9 Planets, moons and other bodies Our Solar System Sun 8 planets ? ~100 moons Thousands of asteroids, millions of icy bodies, comets, … Planets, moons and other bodies Astronomical unit (AU) Average Earth-Sun distance 1.5x108 km 1 km = 0.621 mile or 3280.8 feet @ 93 million miles (92,900,836.17 mi or 149,589,777 km) Light –year (lt-yr) is used for longer distances How far light travels in one solar year Speed of light = 186,282,3976 miles per second 5,880,000,000,000mi or 63,240 AUs !!! Planet classification: size density atmosphere Two main divisions Planets, moons and other bodies 1. FourTerrestrial planets - mostly rocky material, metallic nickel and iron Mercury Venus Earth Mars Planets, moons and other bodies 2. Four Giant Gas Planets - mostly hydrogen, helium and methane Jupiter Saturn Uranus Neptune Pluto is now considered a dwarf planet The order of the planets Mercury Innermost planet 2,439.7 km radius Highly elliptical orbit Average distance ~ 0.4 AU (36 million miles) Orbital period (year) ~ 88 days Sun rise to sun rise (“day”) ~ 176 days Mercury Visible shortly after sunset or before sunrise No atmosphere; No moon 40% smaller than Earth Day hot enough to melt metal 427 C Night cold as liquid nitrogen -173 C Mariner 10 flew past Mercury in 1974 Magnetic field Craters like our moon Cliffs hundreds of kilometers high and long Plains of smooth lava Planets, moons and other bodies 12 Venus Orbital distance ~ 0.7 AU (67 Million miles) Morning and evening “star” Exhibits phases, like the Moon No moons Rotational motion opposite orbital motion Venus Venusian “day” longer than Venusian “year” Visited by numerous probes Mostly CO2 atmosphere, high temperature and pressure Surface mostly flat but varied Venus 3rd brightest in sky Called the sister planet of earth nearly same size and weight Venus Actually hotter than Mercury (900O F) “Greenhouse” effect Clouds of sulfur and CO2 462 C surface temperature Besides “morning star” known as: “witch star” “dragon star” “nearest you can get to hell” (Russian Probe lasted less than an hour) Earth’s Moon 1/6th gravity of earth no atmosphere one orbit takes 27 days 238,857 miles from earth never see dark side 12 Apollo astronauts have walked on the moon (1969-1972) footsteps still there Earth’s Moon Lunar highlands Light colored mountainous regions craters Breccias - rock fragments compacted from meteorite impact Earth’s Moon Maria (“sea”) Smooth dark areas formed from floods of lava Basalt - similar to rock formed from cooling lava on earth Formed about 3.1 – 3.8 billion years ago Surface 3 meters grey dust containing microscopic glass beads formed by bombardment of meteorites Moon Rocks Glass 840 pounds brought back Stages in Formation of the Moon Origin Stage Moon formed from impact of Earth with very large object, perhaps as large as Mars. The moon formed from ejected material produced by collision Stages in Formation of the Moon Molten Surface Stage First 200 million years Lunar surface melted due to rock impact Fewer bombardments, moon surface solidified Craters: result of meteorite impact after formation of crust Stages in Formation of the Moon Molten Interior Stage 3.8 billion years ago Interior melted due to heat generated by radioactivity Cold and Quiet Stage 3.1 billion years ago Last lava solidified Little surface change since Lunar Eclipse Mars – the Red Planet Mars Orbital distance ~ 1.5 AU (141 million mi) One year is 687 days One day is 24 hrs and 37 minutes ½ the size of earth Numerous space probes 2 moons Deimos Phobos Mar’s Moons Mars Geologically active regions: Inactive volcanoes Canyons Terraced plateaus Flat regions pitted with craters Mars Thin atmosphere, 95% CO2--freezes at the south pole Strong evidence for liquid water in past Olympus Mons is 16 miles high dust storms Mars Spacecraft Reconnaissance Orbiter (2004) Spirit and Opportunity Mars Exploration Rovers Found that Mars made of basalt rock and groundwater that is dilute sulfuric acid Confirmed sufficient amounts of water have been present in the past Spirit Rover Spirit ExoMars 2015 Earth and Moon from Mars Jupiter Jupiter ~ 5 AU from Sun One orbit is 12 EY Day is 10 hours Most massive planet 483 million miles 318 times Earth’s mass 200 pound man would weigh 500 pounds Jupiter 4th brightest object in sky Mostly H, He & iron-silicate core “Dynamic” atmosphere H2, He, ammonia, methane, water, Rings are present Jupiter Great Red Spot permanent “hurricane” 2-3 Earths could fit inside spot Jupiter’s Moons 39 widely varying satellites (moons) Galilean moons: Io (active volcanos) Europa Ganymede Callisto 1994 Shoemaker-Levy Comet hits Jupiter Saturn Saturn 9.5 AU from Sun 886.2 million miles 10 hr day 29 1/2 years to orbit Sun Second largest planet 10 times larger than earth Many rings made of ice and rocks Mainly hydrogen and helium Surface similar to Jupiter’s Very cold -285 F Surface has dark and light bands Rapid Rotation causes the equator to bulge Lowest Density = 0.7 that of water (float) Saturn 30 satellites Titan: Largest (Mercury) only moon in solar system with substantial atmosphere (nitrogen) Uranus Uranus Uranus (~19 AU) 3rd largest planet 84 year orbit 16 hour day 27 moons Rings present 1/400th sunlight earth receives Uranus’ Five Major Satellites Neptune Neptune: Blue Planet (~30 AU) 3 billion km 165 years to orbit Sun Great Dark Spot Turbulent atmosphere Very cold surface of frozen hydrogen and helium 13 moons Triton largest moon Pluto Pluto: Smaller than the Moon 70% rock; 30% water ice; thin atmosphere Unusual orbit Tilted 17o from ecliptic Crosses Neptune’s Smaller bodies of the Solar System Comets, asteroids, meteorites Leftover from solar and planetary formation Mass of smaller bodies may be 2/3 of total Solar System mass Bombard larger objects Comet structure Small, solid objects “Dirty snowball” model Frozen water, CO2, ammonia, and methane Dusty and rocky bits Comet structure Comet head Solid nucleus and coma of gas Two types of tails 1. Ionized gases 2. Dust Tail points away from Sun Asteroids Located in belt between Mars and Jupiter Sizes: up to 1,000 km Asteroids Varied composition Inner belt: stony Outer belt: dark with carbon Others: iron and nickel Formed from original solar nebula Prevented from clumping by Jupiter nearby Meteors and meteorites Meteoroids Remnants of comets and asteroids Meteors and meteorites Meteor Meteoroid encountering Earth’s atmosphere Meteor showers: Earth passing through comet’s tail Meteorite Meteoroid surviving to strike Earth’s surface Origin of the Solar System Protoplanet nebular model Stage A Formation of heavy elements in many earlier stars and supernovas Concentration in one region of space as dust, gas and chemical compounds Origin of the Solar System Stage B Formation of large, rotating nebula Gravitational contraction, spin rate increases Origin of the Solar System Most mass concentrates in central protostar Remaining material forms accretion disk Material in accretion disk begins clumping Origin of the Solar System Stage C Solar ignition flare-up may have blown away hydrogen and helium atmospheres of inner planets Protosun becomes a star Origin of the Solar System Protoplanets heated, separating heavy and light minerals Larger bodies cooled slower, with heavy materials settling over longer times into central cores