1. Clouds on Mars (NASA/JPL/Malin Space Science Systems) The Effects of Magma Ocean Depth and Initial Composition on Planetary Differentiation Lindy Elkins-Tanton, MIT E. M. Parmentier, S. Seager, S. Stanley, B. Weiss, M. Zuber NSF Astronomy and NASA Mars Fundamental Research

2. Three stages of early planetary evolution 1. Solidification Process after Abe and Matsui (1985); Solomatov (2000) Emissivity parameterizations from Pujol and North (2003), Hodges (2002), Howard and Kasting (unpub)

3. Different metallic iron core fractions

4. Three stages of early planetary evolution 1. Solidification

5. Three stages of early planetary evolution 1. Solidification2. Cumulate mantle overturns to stability Elkins-Tanton et al. (2005a, b)

6. Gravitational overturn: Nonmonotonic density gradients

7. Overturn creates a laterally heterogeneous mantle Contours of initial depth (proxy for composition) Contours of density Axisymmetic models show: The majority of overturn complete in <2 Myr; small-scale heterogeneities last a long time Before overturn After overturn

8. Depths of origin of lunar volcanic rocks Temperature [C]

9. Water in cumulates Elkins-Tanton (2008)

10. Crustal magnetic field from a Noachian dynamo Purucker et al. (2001)

11. Overturn can produce a core dynamo Stanley et al. (in revision for Science)

12. Three stages of early planetary evolution 1. Solidification2. Cumulate mantle overturns to stability Elkins-Tanton et al. (2005)

13. Three stages of early planetary evolution 1. Solidification2. Cumulate mantle overturns to stability 3. Cooling Planetary surface temperature

14. Water retained vs. degassed during magma ocean solidification: Super- Earths Elkins-Tanton and Seager (2008)

15. Planetary solidification: Time to 98% solid Elkins-Tanton (2008)

16. Surface and atmosphere

17. Surface and atmosphere: 500 km-deep MO, solidification step 1. 10,000 - 1,000,000 years EART H

18. Surface and atmosphere: 500 km-deep MO, overturn and cooling Minimum water in atmosphere: 3.8×10 20 kg water, or 33% of an Earth ocean; 80% of initial water in magma ocean 1. 10,000 - 1,000,000 years 2. overturn: < 1 Myr 3. nearing critical point: (10 Myr) EART H Elkins-Tanton (2008)

19. Three stages of early planetary evolution 1. Solidification2. Cumulate mantle overturns to stability 3. Cooling Planetary surface temperature

20. Effects of size on cooling time PlanetesimalMoonEarth No mafic quench crust is likely to form - without flotation cooling is very fast If plagioclase forms and floats, it may significantly slow planetary cooling r = 10s to 100s km1736 km6378 km Wood et al., 1970; Smith et al., 1970

21. Effects of size on cooling time Water in the magma ocean also suppresses plagioclase stability Without a conductive lid, solidification is very fast - faster than it would have been on the Moon PlanetesimalMoonEarth r = 10s to 100s km1736 km6378 km Elkins-Tanton (2008)

22. Effects of size on cooling time PlanetesimalMoonEarth r = 10s to 100s km1736 km6378 km 26 Al heating melts the body from the inside out Hevey and Sanders (2007) Sahipal et al. (2007) Weiss et al. (submitted)

23. Conclusions 2. overturn: < 1 Myr 3. nearing critical point: (10 Myr) 1. 60,000 - 1 M years Clement surface conditions can be reached within several 10s of Myr of a magma ocean Magma oceans may result in magnetic dynamos on bodies of a range of sizes Magma ocean solidification creates a stably stratified, laterally-heterogenous, damp mantle

24. Water degassed from super-Earth magma oceans Elkins-Tanton and Seager (2008)