In Situ Formation of Mars

A talk I gave at DPS 47 in National Harbor, VA. Half-baked, science talk. Will be much better by the time it's published.

Transcript

1. In Situ Formation of Mars Thomas Barclay NASA Ames Research Center Elisa V. Quintana, William Borucki, Jason F. Rowe, John E. Chambers DPS 2015
2. 2 Early stage dust grains planetesimals ~μm ~1-10 km Middle stage planetesimals planetary embryos ~103 km Final stage embryos planets Classical Solar Nebular Theory Solar System terrestrial planets are thought to have formed In Situ HL Tau
3. The Small Mars Problem N-body models are widely used tools to study the late stages of terrestrial planet formation (i.e., SWIFT, Mercury) Simulations typically form a Mars analog that is far too massive
4. Mars Formed Rapidly Hf/W isotopic evidence from Martian meteorites suggests Mars accreted most of its mass within about 5 Myr. Earth continued to grow for an additional 30-100 Myr (Dauphas and Pourmand 2011)
5. Solar System Chronology 4.567 Gya Birth of Solar System (CAIs) 5 Myr Mars-size embryos, and the bulk of Mars, forms 3 - 7 Myr Cores of giant planets accrete gas envelopes 30-100 Myr Earth grows, Moon-forming impact
6. N-body Models Challenges: 1. Models assume perfect accretion (fragmentation increases N) 2. N-body systems are chaotic, need lots of simulations Our new study addresses these two issues Mercury modified to include state-of-the-art collisions model We performed hundreds of N-body simulations to infer results statistically Chambers (2013) Quintana et al. 2015 (arxiv 1511.03663)
7. 300 Simulations Sun + Jupiter + Saturn (at present orbits) Bimodal protoplanetary disk: 26 embryos (0.1 MEarth ) 260 planetesimals (0.01 MEarth ) Small change in initial conditions in each simulation After collisions bodies can break into fragments as small as 0.5 lunar masses 2 Gyr simulations, where all bodies interact gravitationally and collisionally
8. Sun + Jupiter + Saturn 8
9. Generalized Solar System Look at terrestrial planet formation in a probabilistic manner. 1. Take best-guess initial conditions for disk that have been successful in broadly reproducing the inner Solar System 2. Run a large number of simulations 3. Infer distribution of physical properties (mass, number, water content, etc.) 4. Consider Solar System as one draw from these distributions Not necessary to always form the Solar System, occasionally forming the Solar System is ok to validate model
10. Number and Mass Distributions Mars-like distance Earth-like distance
11. Mars Analogs Mars analog defined as a planet with 0.05-0.2 Mearth, within 1.25-1.75 AU, and accreted no more than 10% of mass after 2 Myr
12. Water on Mars Analogs Water model based on Morbidelli et al. (2001) and Raymond et al. (2004)
13. Conclusions State-of-the-art collision model implemented into Mercury 150 simulations to build statistics Earth-analogs are common (>90%) Mars-analogs not common, but not rare (13%) Small Mars Problem - small number statistics? No theories should be ruled out, as more pieces of the puzzle remain thomas.barclay@nasa.gov (@mrtommyb)
14. Extra Slides 14
15. Effects of Fragmentation Quintana et al. 2015, submitted
16. Impact Energies Earth analogs 35% hit and run 60% mergers 5% head-on Stewart et al. 2015; Quintana et al. 2015
17. Water in Earth and Mars Analogs
18. 18 Water model: Raymond 2004
19. 19 Sun + Jupiter + Saturn
20. 20 Sun-Only
21. 21 Sun-Only
22. Water in Earth and Mars Analogs
23. Iron Mass Fraction
24. 24 Oligarchic Growth