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GENS4001 Astronomy Part 1: The Solar System

GENS4001 Astronomy Part 1: The Solar System Dr Michael Burton Department of Astrophysics School of Physics, UNSW Overview 1 Star (the Sun) 8 + 1 Planets Mercury, Venus, Earth, Mars Jupiter, Saturn, Uranus, Neptune Pluto / Charon ≥ 61 Moons

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GENS4001 Astronomy Part 1: The Solar System

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  1. GENS4001 AstronomyPart 1:The Solar System Dr Michael Burton Department of Astrophysics School of Physics, UNSW The Solar System

  2. Overview • 1 Star (the Sun) • 8 + 1 Planets • Mercury, Venus, Earth, Mars • Jupiter, Saturn, Uranus, Neptune • Pluto / Charon • ≥ 61 Moons • 100,000 (?) Asteroids, 100 million (?) Comets, Solar Wind The Solar System

  3. Formation of the Solar System • Collapse of cloud of gas, dust & ice • 4.6 billion years ago, • Swirling, disk-shaped, • Sun formed at centre of ‘Solar Nebula’. • Inner planets form through accretion of dust particles to planitesimals into protoplanets. • Collisions & cratering dominate for 150 Myrs. • Outer planets form through accretion of gas onto rocky protoplanetary cores.

  4. Our Star, the Sun • Giant ball of plasma undergoing thermonuclear fusion of hydrogen in centre! • Photosphere - visible surface at 6000°C • Chromosphere • Jets of gas (spicules) rise along along boundaries of granules. • Corona - tenuous, hot (2,000,000°C) gas • Blends into Solar Wind The Solar System

  5. The Sun (continued) • Surface features vary with 11-year cycle: • Sunspots: cooler with strong magnetic field, • Solar flare: eruption from sunspot group, • Convection cells, transporting energy outwards. • Energy produced by thermonuclear fusion of 4 H-atoms into He-atom at 8 million °C. • Solar Model well understood: • Fusion in core about 1/4 solar radius in size, • Neutrinos - 1/4 predicted number?

  6. Earth / Moon • Double planet system, tidally interacting. • Plate Tectonics produces continents, oceans, mountains & volcanoes. • Iron rich core producing magnetic field. • Atmosphere of 80% nitrogen, 20% oxygen • Troposphere, stratosphere, mesosphere, thermosphere • Supports life on land, oceans & atmosphere. The Solar System

  7. Earth / Moon (continued) • Magnetosphere surrounding Earth, protecting atmosphere from Solar Wind. • Collision-ejection with giant asteroid, with debris coalescing to form Moon. • Weathering has erased asteroid impacts on Earth but past history still visible on Moon. • Cratered highlands, • Smooth-surfaced Maria, from lava flows. The Solar System

  8. Earth / Moon Phenomena • Phases of the Moon • Orbit about Earth, and Solar illumination. • Eclipses when Sun/Earth/Moon in line: • Lunar eclipses • Solar eclipses (inc. annular) • Tides • Differential gravitational pull of near and far sides of Earth by Moon • Asteroid collisions and mass extinctions?

  9. Effect on culture (romances)? No eclipses or phases - dark skies! Tides only 1/3 current size (from Sun). 12 hour cycle, constant level. Day would still be 6 hours long Enormous tides helped form soup for life? More powerful winds, mountains eroded. What if the Moon didn’t exist? The Solar System

  10. Small (<13,000 km) Rocky (iron core) Thin atmospheres Slow rotation Short years Few moons Warm No Rings Large (>50,000 km) Gaseous (H, He) Thick atmospheres Rapid rotation Long years Many moons Cold Rings The Inner and Outer Planets The Solar System

  11. Mars • No canals, but ancient river channels! • No plate tectonics, resulting in giant shield volcanoes over hot spots, plus canyons. • A few impact craters. • Thin carbon dioxide atmosphere & red dust. • Water must once have flowed - flash floods. • Could life have once existed? • 2 tiny moons (Phobos, & Deimos) are captured asteroids.

  12. Jupiter • The Giant of the planets (not a failed star). • Rapid, differential rotation. • Belts & Zones, methane & ammonia clouds. • Cyclones interface: Red Spot & white ovals. • Strong magnetic fields, huge aurorae. • Gas / Liquid Metallic H / Rocky Core. • Thin, transient dust ring - meteor impacts. The Solar System

  13. Moons of Jupiter • 16 Moons with 4 giants (Galilean satellites). • Io: Volcanic, sulphur-covered, kept molten through tidal heating. • Europa: covered in ice with intricate pattern of cracks • tidal heating supports oceans, life?? • Ganymede: Rock & Ice, past tectonics. • Callisto: Rock, cratered terrain (impacts). The Solar System

  14. Comets and Asteroids • Debris from formation of Solar System. • Asteroids: lumps of rock a few km in size • Most in belt between Mars & Jupiter. • Comets: dirty snowballs of ices and rocks • Primordial, but transient, • Highly elliptical orbits, from Kuiper Belt (50-500AU) or Oort Cloud (to 50,000AU), • Tails only when near Sun (vaporised ice), blown out by the solar wind & sunlight.

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