Planetesimal Collisions as Clues to the Early Dynamic History of the Solar System Fred Ciesla 1 Thomas Davison 2 Gareth Collins 2 David O’Brien 3 1 University of Chicago 2 Imperial College London 3 Planetary Science Institute
Bill Hartmann Art
Planetesimals begat planets.
Planetesimals begat planets.
Planetesimals begat planets.
Planetesimals begat planets.
Planetesimals begat planets.
Planetesimals begat planets.
Asteroids are leftover planetesimals and provide clues to the early solar system.
Asteroids are leftover planetesimals and provide clues to the early solar system.
Few meteorites are perfectly pristine samples. • Meteorites record significant geophysical processing on their parent bodies Melting and Differentiation ✦ of Irons and Achondrites Metamorphism in ✦ Chondritic meteorites • This alters the physical and chemistry properties of the bulk meteorite and their individual components.
Radiogenic heating is believed to be largely responsible for planetesimal processing. • Decay of short-lived radionuclides provided energy to heat early Solar System bodies 26 Al - t 1/2 = 0.7 Ma • • Favored as the most important (or only) heat source 26 Al 26 Mg +Heat
Radiogenic heating is believed to be largely responsible for planetesimal processing. • Decay of short-lived radionuclides provided energy to heat early Solar System bodies 26 Al - t 1/2 = 0.7 Ma • • Favored as the most important (or only) heat source Cold (Type 3 Hot or 26 Al 26 Mg +Heat (Type6 Crust) or Melt)
Models for thermal evolution do fairly well in matching data. • 8 H chondrites with chronological constraints on cooling • Harrison and Grimm (2010) model matched 7 meteorites • H-chondrite parent body constrained to be R p ~100 km and form 2.2 Myr into Solar System evolution
Planetesimal collisions were most frequent and energetic during planetary accretion.
Planetesimal collisions were most frequent and energetic during planetary accretion.
Planetesimal collisions were most frequent and energetic during planetary accretion.
All planetesimals experience collisions throughout the first 100 Myr. Davison et al. (2013) Survived 100Myrs Disrupted 0.4 µ = 1.75 0.12 Probability 0.3 µ = 1377.98 η 0.05 r t = 84.89% 0.2 Probability σ = 32.11 0.08 0.1 0.0 0 4 8 0.04 Number of impactors, r imp > 0.05 r t 1.0 0.8 µ = 0.27 0.00 Probability 1250 1300 1350 1400 1450 1500 0.6 Number of impactors, r imp > 150 m (survivors) η 0.1 r t = 25.21% 0.4 0.05 0.2 0.0 0 1 2 3 0.04 Number of impactors, r imp > 0.1 r t Probability 1.0 0.03 0.8 µ = 0.14 Probability 0.02 0.6 η 0.2 r t = 14.02% 0.4 0.01 0.2 0.00 0.0 0 250 500 750 1000 1250 1500 0 1 2 Number of impactors, r imp > 0.2 r t Number of impactors, r imp > 150 m (disrupted)
Impacts create localized effects, affecting a small fraction of the body. • iSALE hydrocode simulations of impact • 100 km radius dunite target • 10 km radius dunite impactor @ 4 km/s • Equivalent energy of the most energetic impact 100% of bodies of this size would experience. 300 1400 1650 3350 Temperature Density [K] [kg/m 3 ]
Impacts create localized effects, affecting a small fraction of the body. • iSALE hydrocode simulations of impact • 100 km radius dunite target • 10 km radius dunite impactor @ 4 km/s • Equivalent energy of the most energetic impact 100% of bodies of this size would experience. 300 1400 1650 3350 Temperature Density [K] [kg/m 3 ]
Heat from an impact can persist for same time as radiogenic heat. • Solve 2D heat equation • No radiogenic heat • Evolution of post- impact temperature anomaly • 10 Myrs, T peak > 1100K • 20 Myrs, T peak > 900K • 50 Myrs, T peak > 800K • 100 Myrs, T peak > 600K
Heat from an impact can persist for same time as radiogenic heat. • Solve 2D heat equation • No radiogenic heat • Evolution of post- impact temperature anomaly • 10 Myrs, T peak > 1100K • 20 Myrs, T peak > 900K • 50 Myrs, T peak > 800K • 100 Myrs, T peak > 600K
Heat from an impact can persist for same time as radiogenic heat. • Solve 2D heat equation • No radiogenic heat • Evolution of post- impact temperature anomaly • 10 Myrs, T peak > 1100K • 20 Myrs, T peak > 900K • 50 Myrs, T peak > 800K • 100 Myrs, T peak > 600K
Heat from an impact can persist for same time as radiogenic heat. • Solve 2D heat equation • No radiogenic heat • Evolution of post- impact temperature anomaly • 10 Myrs, T peak > 1100K • 20 Myrs, T peak > 900K • 50 Myrs, T peak > 800K • 100 Myrs, T peak > 600K
Heat from an impact can persist for same time as radiogenic heat. • Solve 2D heat equation • No radiogenic heat • Evolution of post- impact temperature anomaly • 10 Myrs, T peak > 1100K • 20 Myrs, T peak > 900K • 50 Myrs, T peak > 800K • 100 Myrs, T peak > 600K
Heat from an impact can persist for same time as radiogenic heat. • Solve 2D heat equation • No radiogenic heat • Evolution of post- impact temperature anomaly • 10 Myrs, T peak > 1100K • 20 Myrs, T peak > 900K • 50 Myrs, T peak > 800K • 100 Myrs, T peak > 600K
Planetesimals were not cold, dense objects in the early Solar System. Most impacts occur early 50 Frequency of all 40 impacts >150 m Impacts per Myrs 30 20 10 0 10 − 1 10 0 10 1 10 2 Time, t [Myrs] 300 1400 1650 3350 Temperature Density [K] [kg/m 3 ]
Planetesimals were not cold, dense objects in the early Solar System. Most impacts occur early 50 Frequency of all 40 impacts >150 m Impacts per Myrs 30 20 10 0 10 − 1 10 0 10 1 10 2 Time, t [Myrs] 300 1400 1650 3350 Temperature Density [K] [kg/m 3 ]
Impact outcomes strongly depend on state of the target body. Ciesla et al. (2013) Temperature [K] 170 1300
Impact outcomes strongly depend on state of the target body. Ciesla et al. (2013) Temperature [K] 170 1300
Impacts may explain anomalous meteorites, provided constraints are met. Temperature [C] Time [yrs]
Impacts may explain anomalous meteorites, provided constraints are met. Temperature [C] Time [yrs]
Impacts may explain anomalous meteorites, provided constraints are met. Temperature [C] Temperature [C] Time [yrs] Time [yrs]
Impacts may explain anomalous meteorites, provided constraints are met. • The anomalous meteorite, Ste. Marguerite, can be explained by impact Temperature [C] Temperature [C] into radiogenically heated body Must occur between ✦ 2-5 Myr after Solar System formation Must be energetic ✦ enough to liberate materials from depth of ~20 km. Time [yrs] Time [yrs]
Evidence for/against other impacts exists in meteorite record. • Thermal alteration of the Iron IAB/Winonaite meteorites (Schulz et al. 2009) Heating to 1000-1100 K at t~14 Myr ✦ • Vaporization and condensation of CB chondrite metal (Campbell et al. Krot et al. (2005) 2001, Krot et al 2005) Metal vaporization requires lots of ✦ energy at ~5 Myr. • Preservation of CV chondrites in crust of large planetesimal over ~50 Myr (Elkins-Tanton et al. 2011) Must avoid impacts almost entirely, ✦ but such bodies tend to experience Elkins-Tanton most impacts, and most energetic et al (2011) ones.
Conclusions/Summary • Planetesimal collisions were most frequent and energetic during the first 10-100 Myr of Solar System history. • Impacts into warm/uncompacted bodies had greater collateral effects than in previous models. Important for debris disks? • Meteorites record a number of energetic (large bodies, high velocity) impacts 3-15 Myr into Solar System history. • Preservation of pristine materials limits number and scale of impacts. • Impacts <1-3 km/s during “compaction phase” of chondrites. • Preservation of “pristine crust” means some bodies avoided significant collisions outright.
Gordon Research Conference on Origins of Solar Systems June 28 - July 3, 2015 Mt. Holyoke College, Massachusetts
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