The Earth’s Place in Space The Earth’s Place in Space 3 Sources of Energy to the Earth: 1. Sun 2. Geothermal 3. Tides 1 •Sun’s energy – created by nuclear fusion in the sun’s core. – reaches earth by radiation (external processes). – drives weather, climate, erosion, photosynthesis. •Geothermal energy – created by radioactive decay (nuclear fission) in the earth’s core. – moves by conduction & convection (internal processes). – drives volcanism, plate tectonics. •Tidal energy – caused by gravitational attraction between the earth’s oceans and the moon and sun. – drives some coastal currents and processes. Energy Flow • Solar Energy (99.985% of Earth’s energy) • Geothermal Energy (0.013%) • Tidal Energy (0.002%) 2 Sources of energy to the Earth Energy Source Tidal Geothermal (total) Conduction Convection Sun (total) Reflected Land, air and sea heating Evaporation Photosynthesis Energy (1012 Watts) 2.7 32.3 21.0 11.3 173,000 52,000 81,000 * * *** 39,960 40.0 Enough energy output by the Sun per second to meet the total electricity demands of the U.S. for 200,000 years! Our neighborhood 3 Origins of our Solar System – Universe formed 10-15 billion years b.p. – Solar system (including Earth) formed 4 -5 (4.6) billion years b.p. from nebula Planetary Accretion – Order of formation – Sun (hydrogen) – inner planets (silicates, oxides, iron-nickel alloys) – outer planets (sulfur, water, methane, ammonium) The Universe • 12-15 billion years old • Millions of galaxies • 400 billion solar systems in galaxy • 9 planets + 61 moons in solar system 4 Birth of the Milky way Our Solar system developed 4.6 billion years ago when the gases of a nebula started to contract and rotate because of gravitational attraction, the sun’s fusion started, and later the planets condensed. 5 2 Basic Types of Planets 1. Terrestrial Planets Mercury Venus Earth Mars 2. Jovian Planets Jupiter Saturn Uranus Neptune Pluto Planets differ in density and composition 6 Density (g cm- 3) 5 4 3 2 1 0 Mer Ven Ear Mar Jup Sat Ura Nep Plu 6 Characteristics of the orbits of the planets… Kepler’s Law of Orbital Harmony p2 = k d3 The farther away from the sun you are, the longer it takes to complete one full revolution around the sun. 7 Kepler’s Laws of Planetary Motion Law of Ellipses All the planets’ orbits are elliptical All have elliptical orbits 94.5 million miles SUN 91.5 million miles Aphelion Perihelion Average distance = 150 million km 8 All rotate in the same direction (moons + sun too) Exceptions = Venus, Uranus, & Pluto rotate slowly clockwise Rotation of sun, planets, & their moons is all in the same direction EARTH SUN MOON All revolve about the sun in the same direction. b. Law of Equal Areas The orbits are nearly circular, but not quite, and the planets travel slightly faster while they are closer to the sun than when farther away (because of the increased gravitational attraction). 9 Newton’s Law of Gravitation M1 M2 F = G R2 Gravitational constant G = 6.672 x 10-11 N m2 kg-2 6.672 x 10-8 cm3 g-1 s-2 Bode’s Law of Planetary Distance Inner planets in such a hot zone close to the sun when they formed that only metals and rocky silicates could condense out and aggregate into planets. Farther out where it was colder, water and lighter “gases” could condense out to form the Outer Jovian Gas Giants. 10