Planetenentstehung

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Planetesimal Formation Through Collisions
Gerhard Wurm (Jens Teiser)
Institut für Planetologie, Münster, Germany
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How do we go from micron dust to km planetesimal?
km planetesimal
(sub)-µm dust
(actually this is comet Wild 2, Stardust, NASA,
JPL)
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Collisions
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• In a growth model,
• some collisions with the largest bodies always
  have to lead to sticking (otherwise no growth)

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• Simple models either assume
• colliding bodies always stick (planetesimal
  formation is easy)
• colliding bodies fragment at a given
  size (planetesimal formation is impossible)

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• but fragmentation and growth can exist side by
  side (Wurm et al., Icarus, 2005).

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A coagulation-fragmentation model for growth and
destruction of boulders (Johansen et al.,
AA, in press)
fragmentation
50 m/s
?
coagulation
?
?
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Wilhelm Tellexperiment
(Teiser and Wurm, in prep)
Dust impacts up to 100 m/s
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v 44 m/s
projectile
mass loss
1 cm
ejectionat impact
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(No Transcript)
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Erosion but target stays big
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• sticking of projectile
• near field damage

only for targets not extended enough(not
important for collisions with boulders)
(Teiser and Wurm, in prep)
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Ejecta are smaller than projectile G
rinding to smaller sizes in a limited number of
steps
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Erosion
Accretion
Teiser and Wurm, in prep.
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This way to planets
(Teiser and Wurm, in prep)
(Blum and Wurm, ARAA, in press)
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(Teiser and Wurm, in prep)
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• Some collisions lead to growth even at a high
  speed 57m/s
• Sub-mm aggregates are important
• Note Growth might work for µm-size dust but
  primitive meteorites (chondrites) consist of
  mm-size chondrules the collisional physics is
  different here

?
(Teiser and Wurm, in prep)