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Variations in Earth's Axis Tilt over Time: How Necessary is a Moon for Climatic Stability?

Jason W. Barnes Assistant Professor of Physics University of Idaho. Variations in Earth's Axis Tilt over Time: How Necessary is a Moon for Climatic Stability?. Earth's Obliquity. Obliquity Drives Seasons. Average Yearly Flux changes as a function of Obliquity. How Can Obliquity Change?.

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Variations in Earth's Axis Tilt over Time: How Necessary is a Moon for Climatic Stability?

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  1. Jason W. Barnes Assistant Professor of Physics University of Idaho Variations in Earth's Axis Tilt over Time:How Necessary is a Moon for Climatic Stability?

  2. Earth's Obliquity

  3. Obliquity Drives Seasons

  4. Average Yearly Flux changes as a function of Obliquity

  5. How Can Obliquity Change? oblateness

  6. A Brief Technical Interlude

  7. Obliquity Changes on Real Earth Varies on ~41,000 year timescales

  8. Net Summer Solar Flux at 65N

  9. Glacial-Interglacial Cycles

  10. MilankovicCycles

  11. Planetary Obliquities are Chaotic • Frequency map analysis gives chaotic region for Earth w/o Moon, 0º - 85º. For Mars, 0º - 60º (Laskar & Robutel 1993). • Uncertainties grow exponentially with time in chaotic zone.

  12. Look What Happened to Mars!

  13. Chaotic Mars Obliquity Evolutions

  14. Chaotic Mars Obliquity Evolutions

  15. Chaotic Mars Obliquity Evolutions

  16. Chaotic Mars Obliquity Evolutions

  17. Chaotic Mars Obliquity Evolutions

  18. Did Mars Ever Really Have Such a High Obliquity? Pavonis Mons

  19. What might the obliquity evolution of a Moonless Earth be like?Timescales

  20. What might the obliquity evolution of a Moonless Earth be like?Changing Axis Angle

  21. Chaos of Obliquity Evolution

  22. Obliquity Range for different planetary rotation periods

  23. Retrograde Rotators are More Stable

  24. Changing Rotation, Initial Axis Azimuth

  25. Chaos as a function of Initial Axis Azimuth

  26. Conclusions • Astronomers call rotational axis tilt ‘obliquity’ • Angle between angular momentum vectors of rotation & orbit • Rotation axis and orbit both precess • When precessions are of commensurate periods, chaos ensues • Current prevailing conventional wisdom is that moon is necessary for obliquity & climatic stability • Assumes solar system • Assumes Earth’s present rotation & obliquity • We use explicit, brute-force numerical integrations to explore the obliquity evolution of Moonless Earths • Typical integrations show variations +/- 10 degrees – survivable. • Some show the predicted large excursions • Retrograde rotators are totally stable • Conclusion: Moons are NOT necessary for climatic stability. They help in some cases, and hurt in others. Need to know full system parameters. • Greatly increases estimates for number of habitable worlds in galaxy

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