Planetary Obliquity Evolution

Transcript

1. Planetary Obliquity Evolution Steven Kreyche University of Idaho Department of Physics
2. Motivation • Exoplanets and the search for life Credit to Dana Berry 2
3. Obliquity: the reason for the seasons 3 Obliquity:
4. Obliquity distribution of the Solar System 4
5. Obliquity variation • What can change planetary obliquity? ◦ Torques from other planets ◦ Change in orbital inclination or ascending node • Spin-orbit resonance ◦ Overlap of rotational axis precession frequency and an orbital frequency ◦ Large-amplitude variation ◦ Rotation axis precession ◦ Depends on rotation period and obliquity 5
6. Spin-orbit resonance 6
7. Retrograde Motivation • Few studies focused on retrograde rotators • Studies that did focus on them found them to be especially obliquity stable • New resonance for eccentric, retrograde rotators 7
8. Periapsis precession 8
9. The cause • Edge-on perspective to planetary orbits • Eccentricity enables precessional torque 9
10. The effect 10 = 2 ሶ − ሶ Ω
11. Predictable relationship • = 2 ሶ − ሶ Ω 11
12. Methods • Simple toy system ◦ Sun, Earth and Jupiter with 3 deg mutual inclination • Run simulations using orbital integrator, smercury ◦ Large parameter space ◦ Computationally expensive • Variables to explore ◦ Eccentricity: 0, 0.1, 0.3, 0.5 ◦ Initial obliquity: 90-180, increments of 5 ◦ Rotation period: 4, 6, 10, 16, 24, 34, 46 12
13. Laboratory apparatus • Unit K-2SO • AMD Threadripper 2990WX • 32 cores, 64 threads • G.SKILL Sniper X memory • 32 GB • MSI Pro Carbon AC motherboard 13
14. A trip to Fourier space • Orbital and rotation axis precession frequencies of Earthmoo 14
15. The physical process 15
16. • Minimum: 0.5° • Median: 5.0° • Maximum: 31.2° • Minimum: 0.4° • Median: 2.0° • Maximum: 5.7° • Minimum: 0.4° • Median: 2.2° • Maximum: 6.3° • Minimum: 0.4° • Median: 3.4° • Maximum: 15.2° Results 16
17. Alternative results • Semi-analytic secular model • 100 Myr at timestep ~2.5% Earth’s orbital period 17 Contributed from Billy Quarles
18. Conclusions, looking ahead • 90% of Earthmoos are relatively stable (experience less than baseline variation) • Earthmoos near resonance experience of order 10-30 degree variations • These variations could be significant, should be considered in future efforts climate models • Knowledge for judging exoplanets • Measuring obliquity for real 18
19. Future plans • Submit to Planetary Science Journal in December • Habitable Worlds grant • Modify smercury code to include tides • Tidal Venus • Tidal Earth • Proposals • Mars • TRAPPIST-1 19
20. Extra: equations • Rotation Axis Precession • ሶ = cos Ψ • ≈ 322 2 ҧ • Annually-averaged Solar flux • ∝ 1 1−2 • Nodal difference • ΔΩ = − Ω 20