N.22 davis paolo-farinella_his-legacy-continues
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PAOLO FARINELLA
Scientist, Humanitarian, Teacher and Friend
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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.
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CONNECTING WITH PAOLOFirst 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 thecollisional evolution of KB population.
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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.
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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...
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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?
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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 ofcollisional disruption (strength vs gravity) regime, required measuring the asteroid size distribution to ever smaller sizes.
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The PLS2 Project
• The lack of a reliable asteroid size-frequency distribution down to km and smaller sizes was limiting collisonalevolution studies and validation of proposed scaling laws.
• Discussions with B. Gladman at theProtostars and Planets meeting in 1999 led to a project to measure the small size distribution of main belt asteroids.
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ON THE ASTEROID BELT’S ORBITAL AND SIZE
DISTRIBUTIONGladman et al (2009). Icarus, 202, 104-118, aka the SKADS
survey.First survey since the Palomar LeidenSurvey (1970) to determine both orbits and absolute magnitudes. Our survey also measured V-R color as a rough guide to asteroid albedos.
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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.
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SKADS 1-SIGMA ACCURACY:
∆A: 0.009 AU∆E: 0.018∆I: 0.17 DEG∆R: 0.065 AU∆HR: <0.3 MAG
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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.
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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
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3) SCALING LAWS AND COLLISIONAL ALGORITHMS
The Problem: Given a collisonbetween two asteroids, what is the
outcome?
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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, forasteroidal strengths.
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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.
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The size-scaling problem
Asteroid diameter
Q*,
Spe
cific
ene
rgy
(erg
/gm
)
10cm 1m 10m 100m 1 km 10 km 100 km104
105
106
107
108
109
Housen & Holsapple (1990)Farinella et al (1982)
Ryan (1992)
Housen & Holsapple (1999)
Benz &
Aspha
ug(19
99)
Love & A
hrens
(1996
)
House
n &Hols
apple
(199
0)
Durda et al
(1998)
Davi
s et a
l (19
85)
Holsap
ple(19
94)
Ryan
&M
elosh
(199
8)
Davis et al (1985)
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WHY WE ARE NOT HYDROCODE BELIEVERS
(YET)Paolo Farinella, D.R. Davis
and Francesco MarzariPresentation at the CD V Workshop,Mt. Hood, OR. 1998.
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Validation of numerical codes for impact and explosion
crateringE. 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.
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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.
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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.
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SNAPSHOTS OF PAOLO
A collection of images of Paolo and others taken over the years.
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"We know a lot less about asteroids than we did ten years ago."
(But that means we will all keep busy for some time..)
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Paolo: By example, he set a standard of excellence as a
scientist, humanist and friend that we may aspire to.
Thank you, dear friend.