Post on 15-Jan-2016
transcript
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