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Planetesimal Collisions as Clues to the Early
Dynamic History of the Solar System
Fred Ciesla1 Thomas Davison2 Gareth Collins2 David O’Brien3
1University of Chicago 2Imperial College London 3Planetary 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 • 26Al - t1/2 = 0.7 Ma
• Favored as the most important (or only) heat source
26Al 26Mg +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 • 26Al - t1/2 = 0.7 Ma
• Favored as the most important (or only) heat source
Hot(Type6 or Melt)
Cold(Type 3
or Crust)
26Al 26Mg +Heat
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 Rp~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.
1250 1300 1350 1400 1450 1500Number of impactors, rimp > 150 m (survivors)
0.00
0.04
0.08
0.12
Pro
babi
lity
µ = 1377.98
� = 32.11
0 250 500 750 1000 1250 1500Number of impactors, rimp > 150 m (disrupted)
0.00
0.01
0.02
0.03
0.04
0.05
Pro
babi
lity
0 4 8Number of impactors, rimp > 0.05rt
0.0
0.1
0.2
0.3
0.4
Pro
babi
lity µ = 1.75
⌘0.05rt = 84.89%
Survived 100Myrs Disrupted
0 1 2 3Number of impactors, rimp > 0.1rt
0.0
0.2
0.4
0.6
0.8
1.0
Pro
babi
lity µ = 0.27
⌘0.1rt = 25.21%
0 1 2Number of impactors, rimp > 0.2rt
0.0
0.2
0.4
0.6
0.8
1.0
Pro
babi
lity µ = 0.14
⌘0.2rt = 14.02%
Davison et al. (2013)
Impacts create localized effects, affecting a small fraction of the body.
Temperature [K]
300 140033501650
Density [kg/m3]
• 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.
Impacts create localized effects, affecting a small fraction of the body.
Temperature [K]
300 140033501650
Density [kg/m3]
• 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.
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, Tpeak > 1100K
• 20 Myrs, Tpeak > 900K
• 50 Myrs, Tpeak > 800K
• 100 Myrs, Tpeak > 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, Tpeak > 1100K
• 20 Myrs, Tpeak > 900K
• 50 Myrs, Tpeak > 800K
• 100 Myrs, Tpeak > 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, Tpeak > 1100K
• 20 Myrs, Tpeak > 900K
• 50 Myrs, Tpeak > 800K
• 100 Myrs, Tpeak > 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, Tpeak > 1100K
• 20 Myrs, Tpeak > 900K
• 50 Myrs, Tpeak > 800K
• 100 Myrs, Tpeak > 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, Tpeak > 1100K
• 20 Myrs, Tpeak > 900K
• 50 Myrs, Tpeak > 800K
• 100 Myrs, Tpeak > 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, Tpeak > 1100K
• 20 Myrs, Tpeak > 900K
• 50 Myrs, Tpeak > 800K
• 100 Myrs, Tpeak > 600K
Planetesimals were not cold, dense objects in the early Solar System.
10�1 100 101 102
Time, t [Myrs]
0
10
20
30
40
50
Impa
cts
per
Myr
s
Most impacts occur earlyFrequency of all impacts >150 m
Temperature [K]
300 140033501650
Density [kg/m3]
Planetesimals were not cold, dense objects in the early Solar System.
10�1 100 101 102
Time, t [Myrs]
0
10
20
30
40
50
Impa
cts
per
Myr
s
Most impacts occur earlyFrequency of all impacts >150 m
Temperature [K]
300 140033501650
Density [kg/m3]
Impact outcomes strongly depend on state of the target body.
Temperature [K]170 1300
Ciesla et al. (2013)
Impact outcomes strongly depend on state of the target body.
Temperature [K]170 1300
Ciesla et al. (2013)
Impacts may explain anomalous meteorites, provided constraints are met.
Tem
pera
ture
[C
]
Time [yrs]
Impacts may explain anomalous meteorites, provided constraints are met.
Tem
pera
ture
[C
]
Time [yrs]
Impacts may explain anomalous meteorites, provided constraints are met.
Tem
pera
ture
[C
]
Time [yrs]
Tem
pera
ture
[C
]
Time [yrs]
Impacts may explain anomalous meteorites, provided constraints are met.
Tem
pera
ture
[C
]
Time [yrs]
Tem
pera
ture
[C
]
Time [yrs]
• The anomalous meteorite, Ste. Marguerite, can be explained by impact 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.
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. 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 most impacts, and most energetic ones.
Krot et al. (2005)
Elkins-Tanton et al (2011)
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