Alberto Cellino – CD VI, Cannes, June 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families Families What can we learn from them?

Alberto Cellino – CD VI, Cannes, June 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families 20 th Century Families

Alberto Cellino – CD VI, Cannes, June 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families 21 th Century Families

Alberto Cellino – CD VI, Cannes, June 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families 20 th 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 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families Major Contributors  Zappalà et al., Bendjoya et al., Williams, Lindblad (identification)  Zappalà et al (reconstruction velocity fields)  Tanga et al. 1999, Campo Bagatin and Petit (size distribution)  Cellino et al (size-velocity relation)  Dell’Oro et al (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 (effects of nearby resonances)

Alberto Cellino – CD VI, Cannes, June 2003 INAF --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 2003 INAF --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 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families The Maria Family

Alberto Cellino – CD VI, Cannes, June 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families 21 th 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 2003 INAF --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 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families Other Contributions  Zappalà et al (No large NEAs from purely collisional mechanisms)  Sliwan and Binzel 2000, 2002 (Spins of Koronis family members)  Nesvorný et al (Discovery of Karin Family)  Cellino et al (Separation of former Nysa-Polana clan)  Milani and Knežević (Steady supply of new proper elements)  Dell’Oro et al (Primordial inter-family collisions)  Carruba et al (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 2003 INAF --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 2003 INAF --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 2003 INAF --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 2003 INAF --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 2003 INAF --Osservatorio Astronomico di Torino Asteroid Families Thesis (20 th Century Families) Antithesis (21 th Century Families) Synthesis ?? W.F. Hegel

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

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