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The Formation of Planetesimals – the Laboratory Perspective
Jürgen Blum Institut für Geophysik und extraterrestrische Physik Technische Universität zu Braunschweig
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Introduction Large bodies in protoplanetary disks form by non-gravitational effects, i.e. by sticking collisions. The collisions among the dust grains are primarily caused by Brownian motion (~ µm), differential drift motions (~100 µm – 1 km), and gas turbulence (predominantly important for equal-sized particles).
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1 AU Weiden-schilling & Cuzzi 1993
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EXPER I MENTS 1 AU Fragmentation + Erosion Erosion
Fragmentation + Growth EXPER I MENTS Fragmentation » «0 Bouncing >0.15 Sticking + Compaction >0.15 Fragmentation + Growth Restructuring/ Compaction Fragmentation + Erosion BPCA = Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion
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EXPER I MENTS 1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm
Fragmentation + Erosion Erosion Fragmentation + Growth EXPER I MENTS 1 m Fragmentation » «0 Bouncing >0.15 Sticking + Compaction >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion BPCA = 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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EXPER I MENTS 1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The fractal growth regime (s1 s2 1 µm…1 mm; v 10-4…10-2 m/s)
Hit-and-stick collisions Mass-size relation m s D with D 2 Narrow (quasi-monodisperse mass spectra) Temporal mass growth follows a power law Blum 2006 1.9 µm SiO2 Blum et al. 1998
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The restructuring/compaction growth regime (s1 s2 1 mm…1 cm; v 10-2…10-1 m/s)
Collisions result in sticking Impact energy exceeds energy to overcome rolling Dust aggregates become non-fractal but are still highly porous Low impact energy: hit-and-stick collisions Intermediate impact energy: compaction Dominik & Tielens 1997 Blum & Wurm 2000
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The bouncing regime (s1 s2 1 cm…1 dm; v 0.1…1 m/s)
Collisions between equal-sized high-porosity dust aggregates do not result in sticking Restitution energy exceeds binding energy Bouncing causes aggregate compaction Heißelmann et al., unpublished data See also poster by Salter et al.
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The fragmentation regime (s1 s2 0.1 m…10 m; v 1…50 m/s)
Collisions between equal-sized dust aggregates are sufficiently energetic to overcome internal aggregate binding energy At onset of fragmentation (v « c), power-law mass spectra have positive slope (a few large fragments) For high-speed collisions (v » c), small fragments dominate Blum & Münch 1993 Speith et al., pers. comm.
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The ballistic particle-cluster aggregation regime (s1 1 µm; s2 10 µm…3 cm; v 10-3…10-1 m/s)
Single particles or small aggregates impacting a large aggregate Experiments: analogous to BPCA is random ballistic deposition (RBD) Hit-and-stick collisions volume filling factor = , very low compressibilities (C Pa) and tensile strength (T Pa) “Dust Cakes” Blum & Kozasa, unpublished data Blum et al. 2006
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The sticking & compaction growth regime (s1 1 µm…3 mm; s2 3 cm…30 cm; v 0.1…3 m/s)
Impacts of dust particles and dust aggregates into much larger dusty bodies are sufficiently energetic to cause material compaction in the projectile and the target Projectiles stick to the target if the penetration depth exceeds the projectile radius Langkowski et al., unpublished data
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The erosion regime (s1 1 µm; s2 > 0.3 m; v 15…60 m/s)
High-velocity collisions between small dust grains and large dust aggregates can result in a mass loss of the large body However, surface shaping due to a continuous bombardment with small dust particles may immunize the target aggregate MASS LOSS erosion at the onset of exposure to dust flux equilibrium erosion 1 mm MASS GAIN Schräpler & Blum, unpublished data
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The fragmentation+growth regime (s1 1 mm…1 cm; s2 30…50 cm; v 12…25 m/s)
When the target aggregate is not too weak, the projectile aggregate fragments upon impact However, part of the impactor remains at the target Güttler & Blum, unpublished data Wurm et al. 2005
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1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm 100 µm 1 cm 1 m
Fragmentation » «0 Bouncing >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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The fragmentation+erosion regime (s1 1 mm…1 cm; s2 > 1 m; v > 25 m/s)
When the target aggregate is too weak, both the projectile and the target aggregate fragment upon impact Wurm et al. 2005
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CONCLUSION 1 AU Diameter Diameter 100 m 1 m 1 cm 100 µm 1 µm 1 µm
Mass loss 100 m 1 AU Mass conservation Fragmentation + Erosion Erosion Fragmentation + Growth Mass gain 1 m Fragmentation » «0 Bouncing >0.15 Sticking + Compaction >0.15 Fragmentation + Growth Diameter 1 cm Restructuring/ Compaction Fragmentation + Erosion BPCA = 100 µm Fractal Growth (Hit-and-Stick) Sticking + Compaction >0.15 BPCA = Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter
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THANK YOU FOR YOUR ATTENTION !
Acknowledgements This work was supported by DFG, DLR and TU Braunschweig Many thanks to Daniel Heißelmann and the ICES team, Roland Speith, Ralf Geretshauser, Takashi Kozasa, Doreen Langkowski, Rainer Schräpler, Carsten Güttler and Gerhard Wurm
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