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The Solar System

The Solar System An Inventory Dozens of moons Thousands of asteroids Trillions of comets What is the Solar System? Answer: The system of objects in the solar neighborhood (near the Sun) What are these objects? One Star Six Planets Nine Planets The Discovered Planets

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The Solar System

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  1. The Solar System An Inventory

  2. Dozens of moons Thousands of asteroids Trillions of comets What is the Solar System? • Answer: The system of objects in the solar neighborhood (near the Sun) • What are these objects? One Star Six Planets Nine Planets

  3. The Discovered Planets • All planets through Saturn known since the ancients – all you have to do is look up to see them • Uranus discovered in 1781 by William Herschel • He wanted to name the planet “Georgium Sidus” after his king and patron, George III of England • Neptune was first seen in 1846 by Johann Galle using predictions by Urbain Jean Joseph Leverrier and John Couch Adams • Pluto was discovered in 1930 by Clyde Tombaugh at Lowell observatory

  4. Size and Scale

  5. Planets • The first step to studying planets? • Compare and contrast • What are important quantities? • You have: • A stick • A tree • A car • A house • What are the important quantities?

  6. Planetary Properties

  7. Density and Mass • What is mass? • Mass is similar to weight, it measures how much stuff an object is made of • Example: A bowling ball and a soccer ball are about the same size, but have different masses • What is density? • Density is mass per volume. It helps to tell you what kind of stuff an object is made of • Example: A log and a tree have different masses (and sizes), but the same density because they are made of the same stuff

  8. Terrestrial Planets • Close to the sun • Small • Mass • Radius • High density • Primarily rocky • Solid surface • Weak magnetic field • Few moons • No rings

  9. Jovian Planets • Far from the sun • Large • Mass • Radius • Low density • Primarily gaseous • No solid surface • Strong magnetic fields • Many moons • Many rings

  10. What About Pluto? • Pluto does not easily fit into either category • Far from the sun (jovian) • Small (terrestrial) • Neither rocky nor gaseous (icy) • One moon • No rings • It is similar is composition to some moons in the outer solar system and its orbit is similar to a group of objects called “Kuiper Belt Objects” or KBOs

  11. Pluto • Only planet in our Solar System that has not been visited by a NASA (or any other) spacecraft

  12. Charon • Largest of any moon in relation to the planet it orbits (1/2 the size of Pluto) • Pluto and Charon are tidally locked to each other (always show the same face) • Charon discovered in 1978 by astronomers at the US Naval Observatory

  13. Formation • Where did the Solar System come from? • First, what observations can we make that will constrain the origin of the Solar System?

  14. Model Requirements • Planet’s are isolated • Planetary orbits are nearly circular • All planetary orbits lie in the same plane • All planets orbit in the same direction as the Sun’s rotation • All planets rotate in the same direction as the Sun • Most moons rotate in the same direction as the planet they orbit • The planetary system is highly differentiated

  15. Differentiation • In general, planets get less dense as they get further from the Sun • They go from being composed of metals, to rocks, to ices, to gases • In other words, they go from being made of things with high melting temperatures to things with low melting temperatures

  16. Highlights of the current theory • Nebular contraction • Mutual gravity causes contraction • Conservation of momentum increases speed • Planetary formation (accretion)

  17. Differentiation revisited • As the solar nebula contracted, the center became hotter than the rest of the cloud • As elements condensed out of the nebulae, temperature determined which could form

  18. Clearing of the nebula • After the planets formed, some small debris still remained. All of these small objects were affected by the gravity of the much larger planets. The debris either: • Hit a planet • Hit the Sun • Was thrown out of the area near the planets – becoming KBOs

  19. Explaining observation • Matching model requirements: • Point (1) is due to planetesimal growth • Points (2), (3), (4), (5), and (6) are due to conservation of angular momentum and gravitational collapse • Point (7) is due to the heating in the nebula • Anomalies: • Retrograde rotation of Venus • Uranus’ axial tilt • The Earth’s moon • All can be explained by impacts of protoplanets into the planet soon after its formation

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