The Formation of Planetesimals – the Laboratory Perspective

1. The Formation of Planetesimals – the Laboratory Perspective Jürgen BlumInstitut für Geophysik und extraterrestrische PhysikTechnische Universität zu Braunschweig

2. 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 (~1 - 100 µm), differential drift motions (~100 µm – 1 km), and gas turbulence (predominantly important for equal-sized particles).

3. 1 AU Weiden-schilling & Cuzzi 1993

4. 1 AU Fragmentation + Erosion Erosion Fragmentation + Growth EXPERIMENTS Fragmentation»0  «0 Bouncing>0.15 Sticking + Compaction>0.15 Fragmentation + Growth Restructuring/Compaction Fragmentation + Erosion BPCA=0.07-0.15 Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion

5. 1 AU 100 m Fragmentation + Erosion Erosion Fragmentation + Growth EXPERIMENTS 1 m Fragmentation»0  «0 Bouncing>0.15 Sticking + Compaction>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion BPCA=0.07-0.15 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

6. 1 AU 100 m EXPERIMENTS 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

7. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

8. The fractal growth regime (s1  s2  1 µm…1 mm; v  10-4…10-2 m/s)  1.9 µm SiO2 • 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 Blum et al. 1998

9. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

10. 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

11. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

12. 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.

13. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

14. 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.

15. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

16. 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  = 0.07-0.15, very low compressibilities (C  100-1000 Pa) and tensile strength (T  100-1000 Pa) “Dust Cakes” Blum & Kozasa, unpublished data Blum et al. 2006

17. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

18. 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

19. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

20. 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

21. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

22. 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

23. 1 AU 100 m 1 m Fragmentation»0  «0 Bouncing>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

24. 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

25. Mass gain Mass conservation Mass loss CONCLUSION 100 m 1 AU Fragmentation + Erosion Erosion Fragmentation + Growth 1 m Fragmentation»0  «0 Bouncing>0.15 Sticking + Compaction>0.15 Fragmentation + Growth 1 cm Restructuring/Compaction Diameter Fragmentation + Erosion BPCA=0.07-0.15 100 µm Sticking + Compaction>0.15 Fractal Growth(Hit-and-Stick) BPCA=0.07-0.15 Erosion 1 µm 1 µm 100 µm 1 cm 1 m 100 m Diameter

26. THANK YOU FOR YOUR ATTENTION ! AcknowledgementsThis work was supported by DFG, DLR and TU BraunschweigMany thanks to Daniel Heißelmann and the ICES team, Roland Speith, Ralf Geretshauser, Takashi Kozasa, Doreen Langkowski, Rainer Schräpler, Carsten Güttler and Gerhard Wurm