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Long-Term Obliquity Variations of a Moonless Earth

Jason W. Barnes Assistant Professor of Physics University of Idaho. Long-Term Obliquity Variations of a Moonless Earth. Planetary Obliquities are C h a o t i c. Frequency map analysis gives chaotic region for Earth w/o Moon, 0º - 85º. For Mars, 0º - 60º (Laskar & Robutel 1993).

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Long-Term Obliquity Variations of a Moonless Earth

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  1. Jason W. Barnes Assistant Professor of Physics University of Idaho Long-Term Obliquity Variations of a Moonless Earth

  2. 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.

  3. Average Yearly Flux changes as a function of Obliquity

  4. Look What Happened to Mars!

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

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

  7. Chaos of Obliquity Evolution

  8. Obliquity Range for different planetary rotation periods

  9. Retrograde Rotators are More Stable

  10. Changing Rotation, Initial Axis Azimuth

  11. Chaos as a function of Initial Axis Azimuth

  12. Conclusions • Obliquity changes of Earth without the Moon are chaotic • Frequency-map analysis shows moonless-Earth 0-85o allowed • Real Mars 0-60o allowed – Mars can access nearly this full range • Current prevailing conventional wisdom in astrobiology is that moon is necessary for obliquity & climatic stability • Assumes solar system • Assumes Earth’s present rotation & obliquity • Assumes 0-85o obliquity without Moon • We use explicit, brute-force numerical integrations to explore the obliquity evolution of Moonless Earths (using modified J. Chambers’ mercury) • 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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