Terrestrial Worlds Orin Harris and Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Spring 2021 c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 1 / 84 Outline Terrestrial Interiors Magnetic Fields Geologic Processes Terrestrial Worlds Terrestrial Atmospheres Review c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 2 / 84 Terrestrial Planets c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 3 / 84 Outline Terrestrial Planets Terrestrial Planets Terrestrial Interiors Sources of Evidence Onion article Planetary Densities S and P Waves Terrestrial Interiors S and P Waves Differentiation Interiors of Terrestrial Plants Q: Differentiation Q: Planetary Cores Earth’s Interior Sources of Internal Heat Earth Heat Evolution Heat Transfer Q: Cooling Volume to Surface Ratio Q: Cooling Planets c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 5 / 84 Q: Rank Sources of Evidence How do we know what is inside? • Average density • Earthquakes • Magnetic fields • Lava flows • Local gravity variations c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 6 / 84 Planetary Densities (ρ = M/V ) 5.52 5.43 5.24 5.0 4.0 3.92 ) 3 3.0 2.0 Density (g/cm 1.0 Mercury Venus Earth Mars Saturn Uranus Neptune tNOs 0.0 Asteroids Jupiter c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 8 / 84 Differentiation • Gravity pulls high-density material to the center. • Lower-density material “floats” to the surface. • Material ends up sorted by density. least dense denser densest c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 11 / 84 Interiors of Terrestrial Plants Earth Venus Mars Mercury Moon Core Mantle Crust highest density medium density lowest density c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 12 / 84 Q: Differentiation What is necessary for differentiation to occur in a planet? A) It must have metal and rock in it. B) It must be a mix of materials of different density. C) Material inside must be able to flow. D) All of the above E) B and C c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 84 Q: Differentiation What is necessary for differentiation to occur in a planet? A) It must have metal and rock in it. B) It must be a mix of materials of different density. C) Material inside must be able to flow. D) All of the above E) B and C c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 84 Q: Planetary Cores The terrestrial planet cores contain mostly metal because: A) the entire planets are made mostly of metal. B) metals condensed first in the solar nebula and the rocks then accreted around them. C) metals sank to the center during a time when the interiors were molten throughout. D) radioactivity created metals in the core from the decay of uranium. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 84 Q: Planetary Cores The terrestrial planet cores contain mostly metal because: A) the entire planets are made mostly of metal. B) metals condensed first in the solar nebula and the rocks then accreted around them. C) metals sank to the center during a time when the interiors were molten throughout. D) radioactivity created metals in the core from the decay of uranium. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 84 Earth’s Interior 3 Earth ρave =5.5 g/cm Core: Fe, Ni,... ρ = 10 − 13 g/cm3 Mantle: O, Si, Mg, ... ρ =3.3 − 5.7 g/cm3 Crust: O, Si, Al, ... ρ =2.7 − 3.3 g/cm3 c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 84 Sources of Internal Heat • Primordial: from planetary formation. Accretion: Kinetic and potential energy of impactors converted into heat. Differentiation: As accreted material separates by density, gravitational potential energy is converted to heat. • Radiogenic: Radioactive decay of uranium, potassium, ...kinetic energy of decay products converted into heat. • Tidal Heating: Not important for terrestrial planets. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 84 Q: Cooling What cools off faster? A) A large cup of coffee B) A small cup of coffee c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 19 / 84 Q: Cooling What cools off faster? A) A large cup of coffee B) A small cup of coffee c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 19 / 84 Volume to Surface Ratio Heat Energy ∝ Volume (V) Heat Loss ∝ Surface Area (S) Cooling Time tcool V ∝ Stcool Surface Area Volume to Surface Ratio: S =4πr2 V 4πr3 r t ∝ = 3 = Volume cool S 4πr2 3 4 V = πr3 3 c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 20 / 84 Q: Cooling Planets What cools off faster? A) A big terrestrial planet B) A tiny terrestrial planet C) They cool at the same rate c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 21 / 84 Q: Cooling Planets What cools off faster? A) A big terrestrial planet B) A tiny terrestrial planet C) They cool at the same rate Smaller worlds cool off faster and harden earlier. The Moon and Mercury are now geologically dead. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 21 / 84 Q: Rank terrestrial planets Rank the five terrestrial worlds in order of size from smallest to largest: A) Mercury, Venus, Earth, Moon, Mars. B) Mercury, Moon, Venus, Earth, Mars. C) Moon, Mercury, Venus, Earth, Mars. D) Moon, Mercury, Mars, Venus, Earth. E) Mercury, Moon, Mars, Earth, Venus. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 22 / 84 Q: Rank terrestrial planets Rank the five terrestrial worlds in order of size from smallest to largest: A) Mercury, Venus, Earth, Moon, Mars. B) Mercury, Moon, Venus, Earth, Mars. C) Moon, Mercury, Venus, Earth, Mars. D) Moon, Mercury, Mars, Venus, Earth. E) Mercury, Moon, Mars, Earth, Venus. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 22 / 84 Bergmann’s Rule “The body mass of a particular species increases with latitude” –German biologist Carl Bergmann 1847. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 23 / 84 Outline Terrestrial Planets Terrestrial Planets Terrestrial Interiors Magnetic Fields The Earth’s Magnetic Field The Earth’s Magnetic Field Magnetic Fields The Van Allen Belts Q: Strongest Mag Field Venusian B-field Geologic Processes Terrestrial Worlds Terrestrial Atmospheres Review c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 24 / 84 The Earth’s Magnetic Field On the surface N S B N m N W E S S c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 25 / 84 The Earth’s Magnetic Field Aurora Borealis (Northern Lights) Click for movie B Aurora Australis (Southern Lights) c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 26 / 84 The Van Allen Belts Image from: Addison Wesley Longman James Van Allen 1914-2006 Van Allen Belt: Doughnut shaped region of energetic charged parti- cles trapped by the Earth’s mag- netic field. Discovered by Van Allen in 1958. Image from: http://www.wikipedia.org c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 27 / 84 Q: Strongest Mag Field Which of the terrestrial worlds has the strongest magnetic field? A) Mars B) Earth C) the Moon D) Venus E) Mercury c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 28 / 84 Q: Strongest Mag Field Which of the terrestrial worlds has the strongest magnetic field? A) Mars B) Earth C) the Moon D) Venus E) Mercury c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 28 / 84 Q: Venus’s Magnetic Field Which of the following most likely explains why Venus does not have a strong magnetic field? A) It does not have a metallic core. B) Its rotation is too slow. C) It is too close to the Sun. D) It is too large. E) It has too thick an atmosphere. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 29 / 84 Q: Venus’s Magnetic Field Which of the following most likely explains why Venus does not have a strong magnetic field? A) It does not have a metallic core. B) Its rotation is too slow. C) It is too close to the Sun. D) It is too large. E) It has too thick an atmosphere. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 29 / 84 Outline Terrestrial Planets Terrestrial Planets Terrestrial Interiors Magnetic Fields Geologic Processes Earth’s Interior Geologic Processes Geological Processes Plate Tectonics Plate Tectonics Plates Ocean Floor Q: Heavily Cratered Q: Tectonic Activity Terrestrial Worlds Terrestrial Atmospheres Review c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 30 / 84 Earth’s Interior rigid crust Depth(km) Layer “plastic” 0-60 Lithosphere 0-35 Crust mantle 35-60 UpperMantle 35-2,890 Mantle liquid core 2,890-6,360 Core Fe-Ni 2,890-5,150 Liquid Outer Core solid 5,150-6,360 Solid Inner Core c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 31 / 84 Geological Processes Processes which shape planetary surfaces: Impact cratering: From Comets or asteroids striking a planet surface. > 150 on Earth. Origin of water? Craters ∼ 10 times as wide as object that create them. Volcanism: Molten rock erupts on the surface. Outgassing. Tectonics: Stretching, compression or movement of lithosphere. Erosion: Breakdown and transport of surface rock from the action of ice, liquid or gas i.e.