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Tidal-Tectonic Processes and Their Implications for the Character of Europa’s Icy Crust

Tidal-Tectonic Processes and Their Implications for the Character of Europa’s Icy Crust. Greenberg, Geissler, Hoppa, and Tufts 2002. Life on Europa. Evolution and State of Europa Two Linked Concepts:. Tidal Heating. global scale. Cycloidal Ridges. Tidal Stresses. Chaotic Terrain.

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Tidal-Tectonic Processes and Their Implications for the Character of Europa’s Icy Crust

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  1. Tidal-Tectonic Processesand Their Implications for the Character ofEuropa’s Icy Crust Greenberg, Geissler, Hoppa, and Tufts 2002 Life on Europa

  2. Evolution and State of Europa Two Linked Concepts: Tidal Heating global scale Cycloidal Ridges Tidal Stresses Chaotic Terrain

  3. Europa, what a place … Life, huh? What do we have to think about to test this idea? Why are the cracks dirty?

  4. Ts Crust qcr Ocean qo qm Silicate Mantle Core qc Tc A Heat Balance Favoring Life? qs ≈ 100 mW / m2 ? • SS heat transfer and crust thickness. • Tidal heating ~ qcr • Conduction v. convection in ice; • thin ice (~10 km); Tidal stresses can break it. • thick ice (~25 km; Nimmo and Manga, 2002); Tidal stresses cannot break it.

  5. An ice thickness near Cilix that does not favor Life? Nimmo et al., 2003

  6. To explore effects of tidally-driven (or any) dynamics, we need a geologic time scale… • Stratigraphy gives relative ages; consistent with intermittent and periodic changes. • Crater counts (and a cratering model) give an age (in principal!); There are not enough of them. • Relaxation of topography around craters (with an ice model). Subjove hemisphere in natural color

  7. Stratigraphy:Crosscutting Relationships From: Prockter et al. (2002)

  8. Stratigraphy:Crosscutting “Lenticulae” PSRD Discoveries (http://www.psrd.hawaii.edu/)

  9. Craters. Not enough for statistics, but v. interesting! Pwyll Crater thin ice Cilix Crater thick ice Manannán Crater very thin ice

  10. We don’t know time very well but the geology permits us to certainly entertain the idea of periodic tidal forcing acting over many length (and time?) scales.Back to tides….

  11. Tidal streses and energetics basics:what we have to think about • The Tidal potential on Europa: a 4+ body problem; nonsynchronous orbit • Tidal heating on Europa from dissipation (can only occur if e>0): • Energy is extracted from the orbit(s), causing them to evolve: • Ganymede, Europa and Io are in a 1:2:4 “Laplace resonance”: How is this maintained? What keeps Europa in a nonsynchronous orbit? -h is fixed: If e goes down (circularize orbit) a must go up (satellite moves out)

  12. P A A p o j o v e P e r i j o v e Europa’s Tides over 1 orbit: Fourier Components Total Tide Total Tide P CC C P Total Tide Total Tide P P

  13. Orbital Evolution: Io-Europa-Ganymede-Jupiter system One Picture for the origin of Laplace Resonance (shown in the next movie): It’s because of Io (I don’t understand this). 1. Io moves outward and becomes tidally-locked with Jupiter. (Dissipation in Io results in a declining e) 2. Europa moves out, in turn. 3. Europa and Io become locked in a resonance and then the pair become locked with Ganymede Question: Io is very active volcanically. This means Qmantle is changing on time scales of 106-108 years. If Q goes down e goes up and a must go down. How stable is this resonance?

  14. Origin of Resonance

  15. Cycloidal Cracking

  16. Cycloidal Cracking

  17. Formation “Dawn” - crack opens perpendicular to tidal force, travels northeast “Noon” - force rotates, crack travels west “Dusk” - force rotations, crack travels southeast “Night” – not enough stress to shear, crack stops Next day: Repeat!

  18. Global Lineaments Cadmus and Minos Conamara region

  19. Thin shell, Constant D Global Lineament Orientation C T T C • Astypalaea Linea • Thynia Linea • Libya Linea • Agenor Linea • Cadmus Linea • Minos Linea

  20. Strike Slip Faulting

  21. Tidal Walking Splitting Right Lateral Shear Compression Left Lateral Shear

  22. (Time-Dependent?) Ridge formation

  23. Ridge Formation

  24. Habital Niches

  25. Tides, water and life?

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