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Surface-interior exchange on rocky and icy planets Edwin Kite University of Chicago Testability...
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Transcript of Surface-interior exchange on rocky and icy planets Edwin Kite University of Chicago Testability...
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