Variations in Earth's Axis Tilt over Time: How Necessary is a Moon for Climatic Stability?
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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
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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?. - PowerPoint PPT Presentation
Transcript of Variations in Earth's Axis Tilt over Time: How Necessary is a Moon for Climatic Stability?
Variations in Earth's Axis Tilt over Time:How Necessary is a Moon for Climatic Stability?
Jason W. BarnesAssistant Professor of Physics
University of Idaho
Earth's Obliquity
Obliquity Drives Seasons
Average Yearly Flux changes as a function of Obliquity
How Can Obliquity Change?
oblateness
A Brief Technical Interlude
Obliquity Changes on Real Earth
Varies on ~41,000 year timescales
Net Summer Solar Flux at 65N
Glacial-Interglacial Cycles
MilankovicCycles
Planetary Obliquities are Chaot
icFrequency 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.
Look What Happened to Mars!
Chaotic Mars Obliquity Evolutions
Chaotic Mars Obliquity Evolutions
Chaotic Mars Obliquity Evolutions
Chaotic Mars Obliquity Evolutions
Chaotic Mars Obliquity Evolutions
Did Mars Ever Really Have Such a High Obliquity?
Pavonis Mons
What might the obliquity evolution
of a Moonless Earth be like?
Timescales
What might the obliquity evolution
of a Moonless Earth be like?
Changing Axis Angle
Chaos of Obliquity Evolution
Obliquity Range for different planetary rotation periods
Retrograde Rotators are More Stable
Changing Rotation, Initial Axis Azimuth
Chaos as a function of Initial Axis Azimuth
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
