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Terrestrial Planets

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Terrestrial Planets Overview of Solar System Object % Total Mass Sun 99.8 • The solar system is a disk Jupiter 0.1 • Rotation of sun, orbits of planets all in Comets 0.05 same direction. All other planets 0.04 • Most planets rotate in this same sense. Satellites & rings 0.00005 (Venus, Uranus, Pluto are exceptions). Asteroids 0.000002 • Angular momentum of pre-solar gas Cosmic dust 0.0000001 cloud. • Terrestrial vs. Jovian (Giant) planets • High vs. low density • Rocks vs. mostly gas • Composition • heavy elements vs. primarily H/He During planet formation in Solar Nebula: Presence of ice • Difference due to distance from Sun. Î more material for core Î could gravitationally attract large masses of hydrogen & helium gas. •(Moon) • Impact craters as clocks Terrestrial Planets • Old highlands (4.1-4.4 billion yrs) • Heavily cratered •Earth • Maria (3.3- 3.8 billion yrs) • Fewer craters • Differentiated: • Rocks from each brought back by • Iron/nickel core Apollo astronauts. • Mantle of lighter rock • Age dating • Thin crust on top • Chemical composition • Tidally locked to Earth • Plate Tectonics • Formation of Moon • Giant Impact is current favorite • Evolution of atmosphere theory… collision between Earth & Mars-sized object. • Thick CO2 Î life Î N2, O2 • Current global warming •Mercury – Greenhouse effect • Closest to Sun, eccentric orbit. – Man-made CO2 • Airless, heavily cratered. • Hot, but (slightly) colder than Hell. • Very dense - mostly iron-nickel core. • Geologically dead (probably) • But rupes Î shrinkage at early time. • Rotates in 2/3 of its orbital period • Tidal locking with a twist. Terrestrial Planets Mars • 50% smaller diameter than Earth (continued) • 1.5 times further from Sun. • Gigantic volcanoes. Venus • 50% highland “continents” • Differentiated like Earth • Tharsis bulge. • But no tectonic plates. • Cracked open to form Valles • Surface mostly studied by radar Marineris. • Large volcanoes • 50% low-lying lava plains. • “Continents” pushed up by tectonic • Atmosphere flows in mantle. •CO, like Venus, but very thin. • Recent lava flows, constant 2 resurfacing. • Liquid water currently impossible. • Crater density Î very young • Climate change surface • Loss of atmosphere – only 800 million yrs old. • Low escape velocity • Solar wind • Thick CO2 atmosphere • Result of runaway greenhouse • Could not retain heat effect. • Water froze out • Keeps surface very hot (900F). • even less heat retained – Lead, brimstone (sulfer) are • 2 Rovers currently searching for molten. evidence of past water. • Retrograde rotation •Life? • Probably due to giant impact. • Viking landers found no sign. • Questionable data in meteorite. The Giant Planets Jupiter – Saturn – Uranus - Neptune • 14-300 x more massive than Earth. • Massive H, He atmospheres • By far the most abundant elements in the solar system. • On top of rock/ice core with 10-15 x mass of Earth. • Lots of weather on Jupiter • Ammonia (NH3) clouds. • Strong winds at different latitudes. (differential rotation) • Cyclonic storms • Great Red Spot –2x size of Earth – 400 yrs so far • Investigated by Galileo probe. Earth Moons Jupiter Callisto • Jupiter’s Galilean moons, as we get Io closer to Jupiter: • Callisto – ice, geologically dead. Europa • Ganymede – ice, but geologically active. Ganymede • Europa – rock, but covered by ice pack over liquid water. •Triton • Io – rock, extreme volcanic activity. • Neptune’s largest moon. • Gradient of properties due to • Retrograde orbit. increased tidal effects & heating • 75% rock, 25% ice. from Jupiter. • Very thin N2 atmosphere. • Jupiter’s 59 other moons are much • Pluto (& Charon) smaller. • No spacecraft visits, so little is • Saturn: 33 known moons known • largest is Titan • Pluto probably quite similar to Triton. •N2 atmosphere. • Similar to Earth’s, but very cold • Charon is half as big as Pluto. (ethane oceans). • Pluto is probably just the • Cassini/Huygens probe to land largest Kuiper belt object. in 2004. • Very low mass. • Eccentric, tilted orbit. • Similar to some comets. Rings Comets • Mostly ice • All 4 giant planets have rings. • Some on highly eccentric orbits • Rings form inside Roche limit: • Spectacular tails when close to Sun. •P2 = a3 Î different parts of a moon • Melted ice is driven off by solar radiation, try to move in orbits with different solar wind. periods. • Most come from Oort Comet Cloud at edge of solar system. • This tears bodies apart unless • Some from Kuiper Belt, just beyond Pluto. gravity (+ internal tensile strength) can hold them together. Asteroids • For orbits inside Roche limit, • Small rocky bodies in orbit about sun. prospective moons are torn apart. • Left over from formation of Solar System. • But rings constantly replenisheed by • Most, but not all, in asteroid belt. material abraded off small moons. • Some cross Earth’s orbit • Jupiter, Uranus, Neptune have very Meteorites thin rings. Saturn has much larger • Asteroids that hit Earth and don’t burn up in atmosphere. rings. • Analyzing them Î • Shepherd satellites • Age of solar system (4.5 billion yrs) • moons sweep out divisions, contain • Initial chemical composition of solar rings through gravitational system. resonances. • Rings made of ice and small bits of dust..
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