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N.34 michel great-influence-of paolo-farinella-in-studies-of

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Talk of the "International Workshop on Paolo Farinella (1953-2000): the Scientists, the man", Pisa, 14-16 June 2010

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N.34 michel great-influence-of paolo-farinella-in-studies-of

  1. 1. Great influence of Paolo Farinella in studies of dynamics of Near-Earth asteroids and collisional processes Vth Catastrophic Disruption Workshop, Oregon, 1998 Pisa, 06/16/2010
  2. 2. • Amors: a>1 AU 1.017<q<1.3 AU • Apollos: a>1 AU q<1.017 AU • Atens: a<1 AU Q>0.987 AU • IEOs: a<1 AU Q<0.987 1000 Objects with D>1 km
  3. 3. Years of studies have shown that asteroids from different regions of the Main Belt (MB) are injected into resonances which transport them on Earth-crossing orbits But once NEOs, what are the main dynamical mechanisms at work? Are there only planetary approaches, as commonly assumed at that time?
  4. 4. • Eros: target of NEAR Hayabusa (NASA/APL) cambe back on June 13th, one day before Paolo’s meeting: • Nereus: initial target of Re-entry capsule in the Muses-C (Hayabusa,JAXA) Woomera desert (Australia)
  5. 5. From Michel&Thomas 1996, AA 307 Semimajor axis close to 1 AU or 0.72 AU Low inclination < 20° ω librates around 0° or 180°
  6. 6. ν13 and ν14 cause great inclination changes
  7. 7. Nature, Vol. 380, 25 April 1996
  8. 8. Distance ν16 To Earth Collision ν4
  9. 9. Proper i, versus proper a, for e=0.1 Longitude of perihelions Longitude of nodes Michel&Froechlé, 1997, Icarus 128
  10. 10. Michel, 1997, Icarus 129 eccentricity, ν3 Polar diagrams Inclination, Overlapping ν13 of ν13 and ν14 = source of chaos
  11. 11. « It makes Boom »!
  12. 12. Experiments using the two-stage light gas gun of ISAS in Japan Setoh, Nakamura, Michel et al. 2010, Icarus 205 Prof. A. Fujiwara: leader of the Science Team of the mission Hayabusa, Pioneer of impact experiments, and good colleague of Paolo!
  13. 13. Comparison with impact experiments on basalt → SPH simulations using 3.5×106 particles Nakamura & Fujiwara 93 Benz & Asphaug 1994! High-res. Runs by M. Jutzi ! largest fragment as a function of impact angle dust removed
  14. 14. Example: a projectile hits a 100 km-size body at 5 km/s (average impact velocity in the MB) From Jutzi, Michel, Benz, Richardson 2010. Red zones are damaged
  15. 15. Gravitational phase: once fragments have been generated they Michel P. et al. 2001. 2002, 2003, 2004 reaccumulate due to their mutual attractions Michel P. 2006, Lecture Notes Physics Michel P. 2009, Lecture Notes in Physics Snapshots centered on the largest fragment; time t=0 to 84 minutes Increase of realism of simulations: model of rigid body allows Reproducingthe shapes of aggregates formed during a collision (Richardson, Michel et al. 2009, PSS 57): Itokawa
  16. 16. Forming asteroid families: Testing the gravity regime P. Michel, W. Benz, P. Tanga and D. Richardson, 2001 1) the parent body is totally disrupted by a catastrophic impact → SPH simulations of impact 2) expanding debris are re-accumulating to form family members time → N-body simulations of re-accumulation Size distribution of an asteroid family: actual and simulated members
  17. 17. Internal structure of small bodies: Characterisation and role Our simulations of asteroid disruptions reproduced for the first time asteroid families and suggest that objects > km are gravitational agregates (rubble piles) Michel et al., Science 294 (2001) Impact energies and disruption outcomes greatly depend on the initial internal structure of the impacted body Michel et al., Nature 421 (2003)
  18. 18. Jutzi, Michel, Hiraoka, Nakamura, Benz, 2009, Icarus 201 Différent kinds of porosity Impact speed: 3 km/s Winter 2010 with A. Nakamura, a good colleague of Paolo
  19. 19. Jutzi, Michel, Hiraoka, Nakamura, Benz, 2009, Icarus 201 Experiment! T = 1.5 ms! Simulation! First validations of a model of fragmentation of porous body
  20. 20. Experiment! T = 8 ms! Simulation! First application at large scale: formation of the crater on the asteroid Stein (Rosetta image) Jutzi, Michel, Benz 2010. A&A 509, L2
  21. 21. Asphaug et al. 2003 Threshold for " which the " largest " fragment has " 50% of the " This parameter still mass of the " needs to be better original body" estimated for monolithic targets, and was not estimated for (thick line with dots:" rubble piles and Benz & Asphaug " porous bodies 1999)" Impact energy threshold for disruption of a solid target vs. Target’s radius
  22. 22. Impact angle: 45° Impact velocity: 3 km/s Q*D=Q0(R/1cm)a + B ρ(R/1cm)b
  23. 23. Q*D=Q0(R/1cm)a + B ρ(R/1cm)b Impact angle: 45°
  24. 24. Impact angle: 45° Jutzi, Michel, Benz, Richardson 2010, Icarus, in press.
  25. 25. Slope Independent On target’s diameter Jutzi, Michel, Benz, Richardson 2010, Icarus, in press
  26. 26. Walsh K., Richardson D.C., Michel, P., Nature 454 Spin-up due to YORP, a variant of the re-discovered Yarkowsky effect by Paolo Final Snapshot of a simulation of spin-up of a km-size aggregate resulting in a binary with similar properties as observed ones 1999 KW4 (Radar Image Ostro et al.) Particles initially at the surface in orange, those initially inside in blank (the pole of the primary should be less weathered than that at the equator)
  27. 27. Thank you!! And thank you, Paolo, for accompanying my researches every day!! Porous versus non-porous!!

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