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

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. • 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

4. 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?

5. • 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)

6. 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°

7. ν13
and
ν14
cause
great
inclination
changes

8. Nature, Vol. 380, 25 April 1996

9. Distance
ν16
To Earth
Collision
ν4

10. Proper i, versus proper a, for e=0.1
Longitude of perihelions Longitude of nodes
Michel&Froechlé, 1997, Icarus 128

11. Michel, 1997, Icarus 129
eccentricity, ν3 Polar diagrams Inclination, Overlapping
ν13 of ν13 and ν14 =
source of chaos

12. « It makes Boom »!

17. 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!

18. 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

19. 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

20. 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

21. 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

22. 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)

26. 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

27. Jutzi, Michel, Hiraoka, Nakamura, Benz, 2009, Icarus 201
Experiment! T = 1.5 ms! Simulation!
First validations of a model of fragmentation of porous body

28. 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

29. 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

30. Impact angle: 45° Impact velocity: 3 km/s
Q*D=Q0(R/1cm)a + B ρ(R/1cm)b

31. Q*D=Q0(R/1cm)a + B ρ(R/1cm)b
Impact angle: 45°

32. Impact angle: 45°
Jutzi, Michel, Benz, Richardson 2010, Icarus, in press.

33. Slope
Independent
On target’s
diameter
Jutzi, Michel, Benz, Richardson 2010, Icarus, in press

34. 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)

36. Thank you!!
And thank you, Paolo,
for accompanying
my researches every day!!
Porous versus non-porous!!