Tidal-Tectonic Processes and Their Implications for the Character of Europa’s Icy Crust Greenberg, Geissler, Hoppa, and Tufts 2002 Life on Europa

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

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

Core Silicate Mantle Ocean Crust qcqc qmqm qoqo q cr TcTc TsTs ? q s ≈ 100 mW / m 2 SS heat transfer and crust thickness. Tidal heating ~ q cr 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. A Heat Balance Favoring Life?

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

To explore effects of tidally- driven (or any) dynamics, we need a geologic time scale… Subjove hemisphere in natural color 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).

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

PSRD Discoveries ( Stratigraphy: Crosscutting “Lenticulae”

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

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….

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)

PerijovePerijove ApojoveApojove PA Europa’s Tides over 1 orbit: Fourier Components Total Tide P P P P CCC

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 Q mantle is changing on time scales of years. If Q goes down e goes up and a must go down. How stable is this resonance?

Origin of Resonance

Cycloidal Cracking

“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! Formation

Global Lineaments Conamara region Cadmus and Minos

1.Astypalaea Linea 2.Thynia Linea 3.Libya Linea 4.Agenor Linea 5.Cadmus Linea 6.Minos Linea Global Lineament Orientation T T C C Thin shell, Constant D

Strike Slip Faulting

Tidal Walking SplittingRight Lateral Shear CompressionLeft Lateral Shear

(Time-Dependent?) Ridge formation

Ridge Formation

Habital Niches

Tides, water and life?