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Ch 7--The Outer Planets 05 Oct 2000 ASTR103, GMU, Dr. Correll 1 What Do You Think • Is Jupiter a “failed star” or almost a star? • What is Jupiter’s Great Red Spot? • Does Jupiter have continents and oceans? • Is Saturn the only planet with rings? • Are the rings of Saturn solid ribbons? 05 Oct 2000 ASTR103, GMU, Dr. Correll 2 Astronomical Telescopes 05 Oct 2000 ASTR103, GMU, Dr. Correll 3 Jupiter 05 Oct 2000 ASTR103, GMU, Dr. Correll 4 Jupiter Outer Layer • Rapid rotation generates dynamic atmosphere • The great red spot – a “hurricane” lasting for centuries • Differential rotation at different latitudes causes colored cloud bands 05 Oct 2000 ASTR103, GMU, Dr. Correll 5 Jupiter’s Atmosphere • Spectroscopy from earth and spacecraft reveal – 86% hydrogen – 13% helium – traces of other simple compounds • methane • ammonia • water vapor 05 Oct 2000 ASTR103, GMU, Dr. Correll 6 Jupiter’s Atmosphere • Convection-movement of material from hotter to cooler regions – just as we saw in the Earth’s mantle – and we’ll see later in the Sun 05 Oct 2000 ASTR103, GMU, Dr. Correll 7 Jupiter’s Interior • Atmosphere--about 150 km of hydrogen, helium and trace gases • Liquid Hydrogen mantle--60,000 km – lower 40,000 km is liquid metallic hydrogen which is electrically conductive, generating the planet’s magnetic field--about 20,000 time stronger than Earth’s • Terrestrial protoplanet core--inner 10,000 km radius, about 50% larger than the Earth! 05 Oct 2000 ASTR103, GMU, Dr. Correll 8 Jupiter’s Moons • Jupiter has at least 16 moons--typical for a large planet • Four largest were discovered by Galileo--the Gallilean moons – – – – Io Europa Ganymede Callisto 05 Oct 2000 ASTR103, GMU, Dr. Correll 9 Jupiter’s Moons 05 Oct 2000 ASTR103, GMU, Dr. Correll 10 Io • Tidal forces generate heat and volcanic activity • Rich in sulfur and sulfur dioxide, hence the yellowish color 05 Oct 2000 ASTR103, GMU, Dr. Correll 11 Europa • Ice and rock crust • Tidal forces heat the moon, making it likely that liquid water is abundant under the ice crust – fracture lines in crust support this theory 05 Oct 2000 ASTR103, GMU, Dr. Correll 12 Ganymede • Largest Jovian moon • Iron-rich core • ice and rock mantle • week magnetic field • thin atmosphere 05 Oct 2000 ASTR103, GMU, Dr. Correll 13 Callisto • Similar to Ganymede--icy and rocky • But, no iron-rich core • Geologically inactive 05 Oct 2000 ASTR103, GMU, Dr. Correll 14 Jupiter’s Rings • Rings comprised of small particles of dust and ice 05 Oct 2000 ASTR103, GMU, Dr. Correll 15 Saturn 05 Oct 2000 ASTR103, GMU, Dr. Correll 16 Saturn • Very similar to Jupiter in elemental makeup and dynamic structure 05 Oct 2000 ASTR103, GMU, Dr. Correll 17 Saturn • Strong magnetic field creates auroral activity as on Earth and Jupiter 05 Oct 2000 ASTR103, GMU, Dr. Correll 18 Saturn’s Rings • Composed of ice, dust and rock • Different rings separated by gaps – due to resonances with gravity of Saturn’s moons – first discovered by Cassini in 1675 05 Oct 2000 ASTR103, GMU, Dr. Correll 19 Saturn’s Moons • Of Saturn’s 22 known moons, only 7 are spherical – the rest probably captured asteroids • Has a dense atmosphere of nitrogen gas – 4 times denser than Earth’s – rich in primitive organic molecules 05 Oct 2000 ASTR103, GMU, Dr. Correll 20 Uranus and Neptune 05 Oct 2000 ASTR103, GMU, Dr. Correll 21 Uranus and Neptune--Interiors 05 Oct 2000 ASTR103, GMU, Dr. Correll 22 Planetary Magnetic Fields • Planetary magnetic fields don’t always line up with rotation axis--and probably change orientation with time 05 Oct 2000 ASTR103, GMU, Dr. Correll 23 Rings and Moons of Uranus • A common feature of large planets 05 Oct 2000 ASTR103, GMU, Dr. Correll 24 Neptune’s Discovery • 1781--Uranus discovered • 1840--Uranus orbit not following predicted path according to Newtonian gravity • 1840-1846--John Adams and Erbain Leverrier predicted the location of an undiscovered planet • 1846--Neptune discovered by Johann Galle at predicted location – Newton’s theory of gravity vindicated! 05 Oct 2000 ASTR103, GMU, Dr. Correll 25 Pluto 05 Oct 2000 ASTR103, GMU, Dr. Correll 26 Pluto and Charon • Pluto is about 8 times as massive as its moon Charon • Similar in composition – rock and ice • No discernable features • Mutually synchronous rotation! 05 Oct 2000 ASTR103, GMU, Dr. Correll 27 What Do You Think • Is Jupiter a “failed star” or almost a star? – Jupiter has 75 times too little mass to shine as a star • What is Jupiter’s Great Red Spot? – The great red spot is a long-lived, oval cloud circulation similar to a hurricane on Earth • Does Jupiter have continents and oceans? – No, Jupiter is comprised mainly of a dense mantle of liquid hydrogen and helium. There is a solid core at it’s center. • Is Saturn the only planet with rings? – No, Four planets (Jupiter, Saturn, Uranus, and Neptune) have rings • Are the rings of Saturn solid ribbons? – Saturn’s rings are all comprised of thin, closely spaced ringlets of ice and dust particles 05 Oct 2000 ASTR103, GMU, Dr. Correll 28 Questions for review • Describe the planet Jupiter, it’s cloud tops, interior layers, magnetic fields and moons. 05 Oct 2000 ASTR103, GMU, Dr. Correll 29