Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Families

What can we learn from them?

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

20th Century Families

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

21th Century Families

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

20th Century Families: General Ideas Families exist and can be reliably identified

Families have a collisional origin

Family members dominate the asteroid inventory at small sizes

The original ejection velocity fields can be reconstructed

Families ejected collisional fragments at high velocities

Families can be (or have been) important sources of NEOs

Families trigger the collisional evolution of the whole population

The original parent bodies were not differentiated

Families have anisotropic structures

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Major Contributors Zappalà et al., Bendjoya et al., Williams, Lindblad (identification)

Zappalà et al. 1996 (reconstruction velocity fields)

Tanga et al. 1999, Campo Bagatin and Petit (size distribution)

Cellino et al. 1999 (size-velocity relation)

Dell’Oro et al. 2000 (Role of families in triggering collision probability)

Bus, Lazzaro and many authors (spectroscopic studies)

Morbidelli et al. 1995, Zappalà et al. 1998; 2000; Gladman et al. 1997 (effects of nearby resonances)

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Families’ size distributions are steeper than Dohnanyi equilibrium slope. Background objects’ size distributions are shallower than Dohanyi’s value

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Size-velocity relation interpreted in terms of a maximum possible amount of kinetic energy delivered to fragments

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

The Maria Family

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

21th Century Families: General Ideas Families exist and can be reliably identified

Families have a collisional origin

Family members do not dominate the asteroid inventory

Families did not eject collisional fragments at high velocities

Families have been strongly modified by evolutionary mechanisms

The original ejection velocity fields can hardly be reconstructed

Family ages can be evaluated

Family members are mostly reaccumulated

Most original parent bodies were not differentiated

Family members may show a preferential spin axis alignement

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Major Contributors “The Yarkovsky team” (Bottke, Vokhroulickí, Morbidelli, Nesvorný, Broz, et al.)

“The hydrocode team” (Benz, Michel, et al.)

“The reaccumulation team” (Tanga, Michel, Richardson, et al.)

“The Cornell team” (Carruba, Burns et al.)

The SDSS and Subaru (Yoshida et al.) teams

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Other Contributions Zappalà et al. 2002 (No large NEAs from purely collisional mechanisms)

Sliwan and Binzel 2000, 2002 (Spins of Koronis family members)

Nesvorný et al. 2002 (Discovery of Karin Family)

Cellino et al. 2001 (Separation of former Nysa-Polana clan)

Milani and Knežević (Steady supply of new proper elements)

Dell’Oro et al. 2002 (Primordial inter-family collisions)

Carruba et al. 2003 (Role of close encounters with large asteroids)

Spitale and Greenberg 2000, 2002 (Analysis of Yarkovsky effect)

Other recent analyses (this meeting)

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Newly-born families are compact

Very soon small family members start to “fly away”

Escaping family members are easy targets of resonant traps

The Yarkovsky concept

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Advantages of 21th Century Family Concepts

Previously unrecognized phenomena are now fully taken into account

Much better agreement with hydrocode results

Possibility of deriving family ages

Agreement with observational bias estimates and observations (SDSS, Subaru)

Natural explanation of the fact that Families do not cross major resonances

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Problems !? Up to which size Yarkovsky is really effective?

Explanations of H vs. Proper elements relations

Need of putting together the effects of events having different, and size-dependent time scales (resonance crossing, resonance-driven dynamical evolution, spin axis collisional realignment.

Real families have e and i distributions which look often more dispersed than preliminary simulations.

Initial family structures not known a priori. Can they be estimated from the distributions of the largest members?

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Family Ages

Young (Koronis?)

Old

Short time for Yarkovsky evolution

Short time for collisional evolution

Current properties diagnostic of

original events

Plenty of time to evolve

Big families and surrounding background

objects should exhibit the same kind of ageing features (size distribution, etc.)

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Thesis (20th Century Families)

Antithesis (21th Century Families)

Synthesis ??

W.F. Hegel

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Urgent tasks New Families Needed (some attempts already done)

Difficulty in identification due to mutual overlapping

Role of Spectroscopy

Need of better estimates of Yarkovsky effectiveness

Interpretation of Proper elements vs. H plots

Better assessment of Primordial vs. Yarkovsky evolution

New photometric data

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families

Alberto Cellino – CD VI, Cannes, June 2003INAF --Osservatorio Astronomico di Torino

Asteroid Families