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

1. PAOLO FARINELLA
Scientist, Humanitarian, Teacher
and Friend

2. HIS LEGACY CONTINUES
I would like to talk about 3 topics where his
legacy and early work contributed in a
major fashion:
1) The Catastrophic Disruption Workshops;
2) The Current Asteroid Size Distribution;
3) Scaling Laws for Catastrophic
Disruption.

3. CONNECTING WITH PAOLO
First Contact: 1981 when PF, PP and EZ
visited Tucson. Science discussions.
1985.Organized the first catastrophic
disruption workshop, Pisa.
1986-2000. Collaborated on problems in
the field of asteroid collisonal evolution.
1995-2000. Collaborated on the
collisional evolution of KB population.

5. ORIGINAL GOALS FOR CD
WORKSHOPS
•Cratering community had well
developed scaling laws; extend to CD.
• Define future experiments.
• Bring in meteoriticists, observers etc.
• Advance our understanding of the
role that catastrophic collisions played
in shaping our solar system.

6. PROGRESS TOWARD CD
GOALS:
A SUMMARY FROM CD7
(2007)
• Wide range of disciplines represented.
• EXPERIMENTS: Steady level of
experiments; validation of scaling . Need
tests for porous bodies.
• SCALING AND MODELING: Very
active community now; good progress.
However...

7. UNRESOLVED PROBLEMS
•The Vesta-Psyche dilemma.
•The “Great Dunite Shortage” and
where are the iron parent bodies?
• Why are there no differentiated
families?
• Does seismic shaking work on
rubble piles?

14. 2) Current Asteroid Size
Distribution
• Terminal boundary condition for all studies
of asteroid evolution.
• Basis for theories of asteroid evolution
since the 1960s, e.g. Anders (1965).
• Increased understanding of the physics of
collisional disruption (strength vs gravity)
regime, required measuring the asteroid
size distribution to ever smaller sizes.

17. The PLS2 Project
• The lack of a reliable asteroid size-
frequency distribution down to km and
smaller sizes was limiting collisonal
evolution studies and validation of
proposed scaling laws.
• Discussions with B. Gladman at the
Protostars and Planets meeting in 1999
led to a project to measure the small size
distribution of main belt asteroids.

18. ON THE ASTEROID BELT’S
ORBITAL AND SIZE
DISTRIBUTION
Gladman et al (2009). Icarus,
202, 104-118, aka the SKADS
survey.
First survey since the Palomar Leiden
Survey (1970) to determine both orbits
and absolute magnitudes. Our survey
also measured V-R color as a rough
guide to asteroid albedos.

19. SKADS OBSERVATIONS
• With 6 nights on the KPNO 3.8m
and the mosaic camera, we
surveyed 8.4 deg**2. Observations
were made in two-3 night blocks
separated by six days.
• We detected, obtained photometry
on and linked 1087 asteroids having
at least a one week baseline.

21. SKADS 1-SIGMA
ACCURACY:
∆A: 0.009 AU
∆E: 0.018
∆I: 0.17 DEG
∆R: 0.065 AU
∆HR: <0.3 MAG

23. SKADS SUMMARY: PAPER I
• We confirm that there is no “bump” in the
magnitude range 14.0<H<18.5. The
asteroids are well represented by a
single power law in this size range.
• We find that there are 9.1x10^5 main-belt
asteroids brighter than H=18.0.

24. SKADS: PAPER II
SKADS II: Bias corrected main belt orbit and
size distributions from a sub-kilometer
asteroid diameter survey
Jedicke et al, in preparation

27. 3) SCALING LAWS AND
COLLISIONAL ALGORITHMS
The Problem: Given a collison
between two asteroids, what is the
outcome?

28. SCALING LAWS EVOLUTION
• Earliest ideas were based on the idea
that asteroids were rocks, thus the
crushing strength was the correct
measure of the energy required to break
them up.
• Piotrowski (1953) assumed “ strong”,
109 erg/gm, and “weak”, 107 erg/gm, for
asteroidal strengths.

29. SCALING LAWS EVOLUTION
• Anders (1965) inverted the problem and
used his models to infer a crushing
strength of 7x 108 erg/gm for asteroids.
• This value was used for asteroids of all
sizes.
• PSI collisional calculations (1970s)
added gravity as the major strength
factor for large asteroids.

30. The size-scaling problem
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ug
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en
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us
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10cm 1m 10m 100m 1 km 10 km 100 km
Asteroid diameter

31. WHY WE ARE NOT
HYDROCODE BELIEVERS
(YET)
Paolo Farinella, D.R. Davis
and Francesco Marzari
Presentation at the CD V
Workshop,
Mt. Hood, OR. 1998.

32. Validation of numerical codes
for impact and explosion
cratering
E. Pierazzo et al (2008). MAPS, 43,12, 1917-
1938.
This project compared results from commonly
used codes on a series of well characterized
experiments. They found an inter-code
variability between 10 and 20% and a similar
discrepancy between the calculation and the
experiment. Overall, the codes are doing a
good job PROVIDED care is taken to match
the code to the problem.

33. BUT:
So far, they have looked only at
cratering calculations, not disruption.
Disruption and scaling comparison is
the next step - provided they get funded
(as always).
I think Paolo would (as am I) be less of
a hydro-skeptic for fragmentation, but
waiting for further confirmation.

34. RECENT SCALING MODELS
• JUTZI ET AL (2008, 2009 AND
2010) used a SPH code to
determine scaling algorithms for
porous bodies. This has been
critically needed with the
realization that many asteroids,
particularly those at small sizes,
are likely “rubble pile” structures.

36. SNAPSHOTS OF PAOLO
A collection of images of Paolo
and others taken over the years.

49. "We know a lot less about asteroids
than we did ten years ago."
(But that means we will all keep busy for some time..)

50. Paolo: By example, he set a
standard of excellence as a
scientist, humanist and friend that
we may aspire to.
Thank you, dear friend.