n.22 davis paolo-farinella_his-legacy-continues

PAOLO FARINELLA

Scientist, Humanitarian, Teacher and Friend

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.

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.

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.

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...

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?

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.

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.

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.

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.

SKADS 1-SIGMA ACCURACY:

∆A: 0.009 AU∆E: 0.018∆I: 0.17 DEG∆R: 0.065 AU∆HR: <0.3 MAG

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.

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

3) SCALING LAWS AND COLLISIONAL ALGORITHMS

The Problem: Given a collisonbetween two asteroids, what is the

outcome?

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.

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.

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)

WHY WE ARE NOT HYDROCODE BELIEVERS

(YET)Paolo Farinella, D.R. Davis

and Francesco MarzariPresentation at the CD V Workshop,Mt. Hood, OR. 1998.

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.

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.

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.

SNAPSHOTS OF PAOLO

A collection of images of Paolo and others taken over the years.

"We know a lot less about asteroids than we did ten years ago."

(But that means we will all keep busy for some time..)

Paolo: By example, he set a standard of excellence as a

scientist, humanist and friend that we may aspire to.

Thank you, dear friend.