Surface-interior exchange on rocky and icy planets

Edwin KiteUniversity of Chicago

Testability requires linking processes of interest (mineralogical, metabolic, …) to atmospheric properties that we can measure; this requires basic theory for surface-interior exchange rate (ζ , s-1) that is currently undeveloped

Today: What can we infer about ζ on planets in general from the 3 data points in hand?

Io, ζ = 10-15 s-1 (NH/RALPH)

Earth, ζ = 10-18 s-1 (Pinatubo Plume)

Enceladus, ζ = 10-16 s-1 (Cassini/ISS)

J. Guarinos

If volcanism ceased, Earth’s biosphere would become undetectable over interstellar distances within 1 Myr

Image: C.-T. Lee

Kasting et al. Icarus 1993Kite, Gaidos & Manga ApJ 2011

Maher et al. Science 2014

Low ζ : Sterile Near-Surface OceanHigh ζ : Potentially Habitable Near-Surface Ocean

e.g. Hand et al. Astrobiology 2007Vance & Brown,

Geochim. Cosmochim. Acta 2013Sleep & Zoback, Astrobiology 2007

GanymedeEuropa

Understanding surface-interior exchange (ζ) after the epoch of formation is necessary to

understand super-Earth atmospheres, H2/H2O ratios, and habitability

Understanding surface-interior exchange (ζ) after the epoch of formation is necessary to link hypotheses to measurable properties

• How much H2 can be produced >108 yr after formation?• Short-period rocky planet atmospheres• Climate stabilization on planets with modest atmospheres

Kasting et al. 1993; Kite et al. 2011; Kopparapu et al. 2013.• Nutrient resupply for chemosynthetic biosphere on planets

with atmospheres that are opaque in the visible • Testability via short-lived species e.g. SO2 • Loss rates vary between gases, so atmospheres could be a

mix of gases left over from accretion and those replenished by volcanism.

Open questions

How do rocky planets dispose of extreme internal heating?Io, ζ = 10-15 s-1:

Heat-pipe volcanism simply relatesζ to heat input; implications for magmaplanets?

What governs the rate of cryo-volcanism?Enceladus, ζ = 10-16 s-1:

Effect of mass and galactic cosmochemicalevolution minor; age moderately important; thickness of volatile overburden critical.

How does silicate volcanism scale toSuper-Earths?Earth, ζ = 10-18 s-1:

Earth, ζ = 10-18 s-1: partial melting by decompressionPlanet’s mantle is cooled by conduction through a thin boundary layerDecompression melting of mantle to form a crust

Korenaga, Annual Reviews EPS, 2013

degassingdegassing

Volatilespartitionefficientlyinto evensmall-%melts

e.g. Earth oceanic crust e.g. Earth continents Venus, Mars …

mantle rocks mantle rocks

crustcrust

Partial melt zones

x

z

Plate tectonics

Stagnantlid

How does melt flux vary with time and planet mass? What is the role of galactic cosmochemical evolution? Can volcanism occur on volatile-rich planets?

Kite, Manga & Gaidos, ApJ, 2009Tackley et al., IAU Symp. 293, 2014Stamenkovic, 2014

How Earth-like melting scales to Super Earths

ΔT

P/ρgk(Tp – Ts)/Q

Mantle parcel ascendingbeneath stagnant lid

Mantle parcel ascendingbeneath mid-oceanridge

Melt fraction

Plate tectonics

Stagnantlid

Kite, Manga & Gaidos ApJ 2009

Simple thermal model and melting model

Parameterized convectionmodels tuned to reproduce 7kmthick oceanic crust on today’sEarth

Cooling rate 50-100 K/GyrKorenaga AREPS

2013

Assumptions: Melting with small residual porosity, melts separate quickly, and suffer relatively little re-equilibration during ascent.

.X(T,P):McKenzie & Bickle, 1988Katz et al., 2003pMELTS (Asimow et al.,2001)

Kite, Manga & Gaidos ApJ 2009

Super-Earth volcanism: plates versus stagnant lid

PLATES

STAGNANTLID

Kite, Manga & Gaidos, ApJ, 2009

Effect of galactic cosmochemicalevolution minor; white dwarfs validate chondritic assumption

beyond limitsof melt fraction databases

=

Kepler-444Tau Ceti

Earth today

Volatile-rich planets lack volcanism

Kite, Manga & Gaidos, ApJ, 2009;Ocean and planet masses (black dots) from accretion simulations of Raymond et al., Icarus, 2006

Erro

r on

Kepl

er-9

3 ra

dius

CO2 degas

H2O degas

Maximumvolcanism

Zerovolcanism

Mas

s ab

ove

vola

tile-

rock

inte

rfac

e (E

arth

oce

ans)

Many “Earths” defined using 5% radius error will lack volcanism

Jacobsen & Walsh in AGU EarlyEarth monograph 2015

This ensemble is Earth-tuned, at least conceptually Giant impacts introduce further scatter

(Stewart group, Schlichting group, …)

Both hydrogen mass fraction and water mass fraction are very variable:

Mantle rock

Volcanism-free planets are primed for H2 production via water-rock reactions

Serpentinization: rapid for mantle rocks, slow for crust.Serpentinization rare on Earth because mantle rocks are usually shrouded by crust

z

D. Kelley et al. Nature 2001

T = 394K

T < 1000K

Aqueous phase(supercritical,molecular water)

Moist hydrogen

photosphere

Habitable

Hypothetical

L. Rogers, PhD thesis, 2012Kreidberg et al. ApJ 2014 Mantle rock

z

T = 394K

Stratificationexpected

Aqueous phase(supercritical,molecular water)

Moist hydrogen

photosphere

Habitable

Newton & Manning, GCA 2002

T > 1000K

Open questions

How do rocky planets dispose of extreme internal heating?Io, ζ = 10-15 s-1:

Heat-pipe volcanism simply relatesζ to heat input; implications for magmaplanets?

What governs the rate of cryo-volcanism?Enceladus, ζ = 10-16 s-1:

Effect of mass and galactic cosmochemicalevolution minor; age moderately important; thickness of volatile overburden critical.

How does silicate volcanism scale toSuper-Earths?Earth, ζ = 10-18 s-1:

Io (Jupiter I) ,ζ = 10-15 s-1: fastest surface-interior exchange rate known

L. Morabito et al., Science 1979

Total heat flow Q = 40 x Earth

(Veeder et al. Icarus 2012)

Conductive lithosphere would be 1500/(Q/k) ~ 2 km thickBut mountains are up to 18 km high!

Plume

Surface-interior exchange in heat-pipe mode on Io:explaining ζ = 10-15 s-1

O’Reilly & Davies, GRL, 1981

cold, frozensubsiding

crust (2 cm/yr)

Asce

ndin

g m

agm

a

Moore et al. in Lopes & Spencer, “Io after Galileo,” 2007.

From tidal heating calculations

Slow surface-interior exchange

Fast surface-interior

exchange: cold, strong crust

Temperature

Dep

thx

z

thin flows

ζ is more predictable for massive and/or young rocky planets than for old and/or small rocky planets

Kite, Manga & Gaidos, ApJ 2009Moore et al. J. Geophys. Res. 2003Spreading rate (m/yr):

Advective cooling(Io-like)ζ ~ Q

Conductive cooling(Earth-like)

ζ = ζ(Q, X, T(t,z) …)

No heat pipesWith heat pipes

BATCHEVAPORATION

FRACTIONALEVAPORATION

How does ζ affect magma planet / disintegrating planet observables?Kepler-10b, -32b, -42c, -78b, -407b , CoRoT-7b, KIC 12557548b …

Rappaport et al. 2012Perez-Becker & Chiang MNRAS 2013Sanchis-Ojeda et al. ApJ 2014Croll et al. arXiv 2014Bochinski et al. ApJL 2015

Low ζ: Thin Al + Ti + O atmosphere Slow mass loss

High ζ: Thick atmosphere including Na, K Fast mass loss

strong time variability and outbursts?

Rathbun & Spencer 2003Loki Patera, Io: a periodic volcanoJ. Rathbun et al. GRL 2002

How does ζ affect magma planet / disintegrating planet observables?

400 km across

Open questions

How do rocky planets dispose of extreme internal heating?Io, ζ = 10-15 s-1:

Heat-pipe volcanism simply relatesζ to heat input; implications for magmaplanets?

What governs the rate of cryo-volcanism?Enceladus, ζ = 10-16 s-1:

Effect of mass and galactic cosmochemicalevolution minor; age moderately important; thickness of volatile overburden critical.

How does silicate volcanism scale toSuper-Earths?Earth, ζ = 10-18 s-1:

Enceladus (Saturn II), ζ = 10-16 s-1: the only known active cryovolcanic world

Cassini ISS

Problems:Why ζ = 10-16 s-1 ?Persistence of the eruptions through the diurnal tidal cycleMaintenance of fissure eruptions over Myr timescalesPreventing subsurface ocean from refreezing over Gyr

addressedtoday

longertimescales

ancient,cratered

South polar terrain:

no craters

4 continuously-active “tiger stripes”

Cryo-volcanism on Enceladus has deep tectonic roots

Density = 1.6 g/cc

Probing tectonicsVolcanism

Geology ?Tectonic mode:

Seismicity

Geology Geomorphology

Gravity

EarthEnceladus

10 km

(4.6±0.2) GW excess thermal emission from surface fractures (~10 KW/m length; all four tiger stripes erupt as “curtains”)

Spencer & Nimmo AREPS 2013Porco et al. Astron. J. 2014

South polar projection

Hotspots up to 200KNo liquid water at surfaceLatent heat represented by plumes < 1 GW

to Saturn

130 km

Key constraint #1: avert freeze-up at water table

x

z

watertable

(30±

5) k

m

Kite & Rubin, in prep.

?

5 x

phaseshift 55°

Key constraint #2: match tidal response of plumes

smaller plume grains

larger plume grains

(period: 1.3 days)

base level

NAS

A/JP

L

Ascent-time correction < 1 hour

New model: Melted-back slotCompression Tension

ocean ocean

supersonic plumesupersonic plume

water level fallswater level rises

x

z

Attractive properties:• Matches (resonant) phase lag• Eruptions persist through 1.3d cycle• Matches power output• Pumping disrupts ice formation• Slot evolves to stable width

Kite & Rubin, in prep.

σn σn

Long-lived water-filled slots drive tectonics

COLD, STRONGICE

WARM, WEAKICE

x

z

Kite & Rubin, in prep.

net flow<<

oscillatoryflow

Slot model explains and links surface-interior exchange on diurnal through Myr timescales

Gravityconstraint

Observedpower

Inferredpower

Predicted Myr-averagepower output

matches observed phase lag slot aperture varies by >1.5

Kite & Rubin, in prep.

Future research requiring only existing data: ζ = ζ (R, X, t …)

Temperature at volatile-rock interface

Pres

sure

at

vol

atile

-roc

k in

terf

ace

Earth, Io,Enceladus

Subduction-zonethermodynamics

Magmaoceanography

Summary: ζ (R, X, t) = ?

How do rocky planets dispose of extreme internal heating?Io, ζ = 10-15 s-1:

Heat-pipe volcanism simply relatesζ to heat input; implications for magmaplanets?

What governs the rate of cryo-volcanism?Enceladus, ζ = 10-16 s-1:

Effect of mass and galactic cosmogenicevolution minor; age moderately important; thickness of volatile overburden critical.

How does silicate volcanism scale toSuper-Earths?Earth, ζ = 10-18 s-1:

Turbulent dissipation within tiger stripes may explain the power output of Enceladus.

http://geosci.uchicago.edu/~kite

Bonus Slides

Blurb

• Purpose of growing research group• Distinctive because we do both climate

modeling and data analysis “in-house”• U. Chicago planets-and-exoplanets research

A CHALLENGE TO MODELERS: ζ (r, t, m)

dry wet

Where does habitability stop?

Sketch of processes that matter

Possible hints(?) at a research program?Subduction-zone

experimental petrology

1D radiative-convective modeling of H2-H2O- “rock” measurements

Glenn Extreme Environment Rig

Heat production vs. heat loss

• Compare to magmatic activity

Outline (for own reference …)

• Define Zeta parameter• Relate this to things we might be able to

measure (white dwarfs, radiogenics)• Scaling ongoing rock magmatism in the solar

system• Scaling ongoing cryo-volcanism in the solar

system• Exchange scenarios without solar system tie

points (Volatile-rich planets, Magma planets)

Ikoma & Genda 2006

Is plate tectonics possible?Valencia & O’Connell (EPSL, 2009) show that faster plate velocities on super-Earths don’tlead to buoyant plates - provided that Tc < 0.16 Tl at the subduction zone.

We find that this limit is comfortablyexceeded, and plates arepositively buoyant at the subductionzone when M ≥ 10 Mearth

Differing results related tochoice of tν.

Galactic cosmochemical evolution

Time after galaxy formation (Gyr)

[X]/

[Si],

nor

mal

ized

to E

arth

10

1

Eu is a spectroscopic proxy for r –process elements such as U & Th. Eu/Si trends indicate that the young Galaxy is Si – poor.

Effects on present-day conditions:Including cosmochemical trends in [U] and [Th] lowers mantle temperature (Tm) by up to 50 K for young planets, while raising Tm by up to 40 K for old stars, compared to their present-day temperature had they formed with an Earthlike inventory of radiogenic elements.

Acts to reduce the effect of aging.

Frank et al. Icarus 2014

Earth, ζ = 10-18 s-1: partial melting by decompression

Decompression melting of mantle to form a crust

Langmuir & Forsyth, Oceanography 2007

degassing degassing

Volatilespartitionefficientlyinto evensmall-%melts

water source

surface

usually frozen vs. sustained melt pool?

intermittent vs. steady?

duty cycle? timescale?

habitability

astrobiology

Understanding the sustainability of water eruptions on Enceladus is important

iceshell

Surface-atmosphere exchange does not dominate!

• The heart of the problem