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Themes of Our Solar System

Part 4: Tidal Forces. Themes of Our Solar System. Quick Question: What body has the most active volcanoes in our solar system?. Earth Venus Mars Io (a moon of Jupiter). From New Horizons , 2008. From Galileo , 1999.

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Themes of Our Solar System

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  1. Part 4: Tidal Forces Themes of Our Solar System

  2. Quick Question: What body has the most active volcanoes in our solar system? • Earth • Venus • Mars • Io (a moon of Jupiter) From New Horizons, 2008 From Galileo, 1999

  3. Far, far away, 500 million miles from the sun, a small body the size of our Moon is the most geologically and volcanically active body in the solar system…. Why?

  4. A Review of Gravity

  5. An Example: Jupiter’s Closest Moon, Io

  6. Gravity Depends Dramatically on Distance

  7. Effect of “Gravity Difference”: Shape Distortion (aka – “Tides”) Tidal Forces - When different parts of a body experience different forces of gravity due to different distances from another body

  8. Effects of Tidal Forces on a Moon • The stretching and contraction of the moon cause friction in its interior, generating heat. The heat may be enough to melt the mantle and keep the moon geologically “alive”. Example: Volcanism of Io

  9. A Result of Tidal Forces:Internal heat creates volcanoes From New Horizons, 2008 From Galileo, 1999

  10. Another Effect of Tidal Forces

  11. More Effects of Tidal Forces on a Moon 2. The moon’s orbit around the planet slows and the moon slowly spirals outward. Example: Moon and Earth

  12. The Moon and Earth System:Drifting Apart The Moon is spiraling away from Earth at a rate of 2 inches per year. 4 Billion Years Ago: Moon was 15,000 miles from Earth Today: Moon is 240,000 miles away Back then… The Moon would’ve been 16 times bigger from our point of view! Tides would’ve been 2 miles high!

  13. Why is the Moon’s Orbit Slowing Down? The Moon orbits faster than the Earth can change its shape. The Earth’s bulge lags behind the moon, pulling on it and slowing it down.

  14. More Effects of Tidal Forces on a Moon 3. The rotation of both planet and moon slow down, too. Example: Moon and Earth

  15. As the World Turns Every 100 years, our days get longer by 0.002 seconds.

  16. More Effects of Tidal Forces on a Moon 4. The same side of the Moon always faces Earth. The Moon has stopped spinning on its axis! Example: Moon and Earth

  17. A Coincidence? • Lunar “day” (period of rotation) = 29 days • Period of revolution about Earth = 29 days The Moon experiences “synchronous rotation” with the Earth. Being smaller, the Moon achieved synchronous rotation fairly quickly. What about Earth?

  18. More Effects of Tidal Forces on a Moon 5. Eventually, the same side of the Earth will always face the Moon. Example: Moon and Earth

  19. In the Future… In ~ 1 trillion years… • The Earth day will be ~1000 hours long. • 1 Earth day will be = 1 lunar month • The moon will be ~320,000 miles away (1.3 times farther) • The Earth and Moon will be “tidally locked” • Other examples: Pluto and Charon, Jupiter and its near moons

  20. More Effects of Tidal Forces on a Moon 6. Destruction??? Example: Rings of Saturn?

  21. Extreme Tidal Forces:Stretched to the Breaking Point

  22. The Roche Limit • Distance from a planet in which no moon can exist without being broken apart by tidal forces • Usual distance: 2.4 times radius of planet: Roche Limit Planet Moon

  23. Roche Limit: 180,000 miles A Coincidence? Saturn’s Roche Limit: 180,000 miles Roche Limit: 180,000 miles Ring Distance: 181,000 miles Distance of Saturn’s Rings: 181,000 miles

  24. Forming Rings

  25. Saturn’s Rings Constantly Changing. Role of “Shepherd Moons”

  26. What About Earth and the Moon? Earth’s Roche Limit: ~ 8,000 miles 8,000 miles 329,000 miles (not to scale) The Moon is WELL outside the Earth’s Roche limit, so it’s in no danger!

  27. What About Earth and our Satellites? 8,000 miles ISS 230 miles (not to scale) Why doesn’t the Space Station break apart? Welded (and bolted) steel is stronger than rock and dirt clumped together Earth’s Roche Limit: ~ 8,000 miles

  28. What About the Sun and Mercury? The Sun’s Roche Limit: ~400,000 miles 400,000 miles Mercury’s Closest Approach: 28 million miles (not to scale)

  29. The Rings of Our Solar System

  30. JupiterBig on size, but wimpy on rings

  31. SaturnThe Planet with Ears

  32. Uranus, on its side!

  33. Neptuneas seen by Voyager 2

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