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Magmatism on Super-Earths: What do we expect to see?

Magmatism on Super-Earths: What do we expect to see?. Edwin Kite & Michael Manga (UC Berkeley)  Eric Gaidos (U. Hawaii). Queloz et al., A&A, 2009. exoplanet.eu, 12/2/2009. Radiogenic heating , stellar insolation, and tidal forcing. Radiogenic heating dominates:.

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Magmatism on Super-Earths: What do we expect to see?

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  1. Magmatism on Super-Earths: What do we expect to see? Edwin Kite & Michael Manga (UC Berkeley)  Eric Gaidos (U. Hawaii) Queloz et al., A&A, 2009 exoplanet.eu, 12/2/2009

  2. Radiogenic heating , stellar insolation, and tidal forcing

  3. Radiogenic heating dominates: How does melt flux vary with time and planet mass? Is plate tectonics possible on Super-Earths? What is the role of galactic cosmochemical evolution? What is the role of oceans? Kite, Manga & Gaidos, Astrophysical Journal, 2009 Valencia & O’Connell, EPSL, 2009 Papuc & Davies, Icarus, 2008

  4. Parameterized convection Models tuned to reproduce 7km thick oceanic crust on today’s Earth Tν = 43K Thermal model Melting model Assumptions: Melting with small residual porosity, melts separate quickly, and suffer relatively little re-equilibration during ascent. .X(T,P) from: McKenzie & Bickle, 1988 Katz et al., 2003 pMELTS (Asimow et al.,2001)

  5. k(Tp – Ts)/Q P/ρg Competing effects of greater planet mass Stagnant lid Plate tectonics ΔT Melt fraction Mantle parcel ascending beneath mid-ocean ridge Mantle parcel ascending beneath stagnant lid

  6. PLATES Results: Plate tectonics versus stagnant lid Katz et al., 2003 productivity model STAGNANT LID Kite, Manga & Gaidos, ApJ, 2009

  7. Valencia & O’Connell (EPSL, 2009) show that faster plate velocities on super-Earths don’t lead to buoyant plates - provided that Tc < 0.16 Tl at the subduction zone. We find that this limit is comfortably exceeded, and plates are positively buoyant at the subduction zone when M ≥ 10 Mearth Differing results related to choice of tν. Is plate tectonics possible?

  8. 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. 10 Galactic cosmochemical evolution [X]/[Si], normalized to Earth 1 Time after galaxy formation (Gyr)

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

  10. ESO (artist’s impression) Stellar heating dominates: HD 189733b (1.13 MJup) http://www.jach.hawaii.edu Knutson et al., Nature, 2007

  11. Temperature Detectability of ponds with isothermal surface temperature Temperature Temperature Atmospheres have wavelength-dependent phase curve shape Magma ponds have wavelength-independent phase curve shape

  12. Barnes et al., ApJL, 2009 Minimum heating: 0.04 W/m2 Maximum heating: 2 W/m2 (Io) Tidal habitable zone Insolation habitable zone Combined habitable zone Tidal heating dominates: Q’ is fixed (500). Open question: Can tidal heating initiate a runaway greenhouse? Hemming et al., ApJ, 2009 Barnes et al., ApJL, 2009

  13. Summary Minor effect of planet mass on crustal thickness  Provided plate tectonics operates; buoyancy may be a problem Galactic cosmochemical evolution probably less important  Si accumulates over galactic evolution, U & Th reach steady state Massive oceans suppress volcanism  Important, e.g., for migrating planets (“ocean planets”) Magma ponds may be probe of composition Not known if ponds are close to isothermal Stable to TPW? Tidal heating can drive geodynamics and perhaps climate  See recent Henning et al. paper on arxiv

  14. Backup slides (removed from online version)

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