Presentation

CD7, Alicante, 26/June/2007

Laboratory Impact Disruption Experiments Towards Understanding the Impact Process of Porous Bodies Akiko M. Nakamura Graduate School of Science, Kobe University

Plan zIntroduction zA view of Asteroid 25143 Itokawa zAn experimental determination of Weibull parameters zLaboratory impact disruption experiments of porous targets

Laboratory Impact Experiments of rocks vs Numerial Simulations

Projectile Nylon 7mmφ Target Basalt 6cmφ Impact velocity 3.2km/s Impact angle:α =30 45 60°

(Nakamura and Fujiwara, Icarus, 1991)

Laboratory Impact Experiments of rocks vs Numerial Simulations

Typical “core” fragment from the laboratory experiment

(Benz and Asphaug, Icarus, 1994)

Impact Strength

Gravity dominated

Present Itokawa

Strength dominated

(Benz and Asphaug 1999)

zIntroduction zA view of Asteroid 25143 Itokawa zAn experimental determination of Weibull parameters zLaboratory impact disruption experiments of porous targets

Asteroid 25143 Itokawa (535x294x209m) “Rubble-Pile” (Fujiwara et al., Science, 2006) z Bulk porosity 40 z Largest boulder size 50 30 20 (cannot be ejected from any crater candidates on Itokawa)

ISAS/JAXA

Boulders and Fragments (Nakamura et al., 2007, EPS, in press.)

2cm

2cm

Crack width/boulder width

Fully cracked state (Holsapple and Housen, Icarus, 1999))

2m

z Shapes and texture of boulders and laboratory fragments are very similar. → The present boulders are the ones that have survived for disruption and re-accumulation processes, even if Itokawa was not the first generation-rubble-pile*. * the one originated from a non-rubble pile body → What are the physical properties of the parent body of the boulders (and Itokawa)?

zIntroduction zA view of Asteroid 25143 Itokawa zAn experimental determination of Weibull parameters of Yakuno basalt targets used in previous laboratory impact experiments (Nakamura, Michel, and Setoh, JGR, 2006)

zLaboratory impact disruption experiments of porous targets

How to determine the Weibull parameters?

z Simulation fits to laboratory data z Asuuming the Grady-Kipp model and derive it from the strain dependent strength m

σ ∝ ε 3+ m

z Size dependence of static strength (e.g. Holsapple and Housen, Icarus, 1999

σ ∝ ( kV )

−

1 m

, V: volume of the specimen

Weibull parameters (m,k)

(Asphaug et al., in Asteroids III, 2002)

Another method: the Weibull’s original method

Measurements “Brazil disc test” Tensile stress =2F/πdl

Disks diameter (d)=10mm, and thickness (l)=5mm

F

Results at loading rate=1mm/min

A comparison with previous values

[MPa]

[cm-3]

ln( kV ) / m ∝ ln( σ N )

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