The Collisional Evolution of Trans-Neptunian Objects

Invited Review
TNO 2006 International Workshop, Catania, Italy

David P. O'Brien
Planetary Science Institute, Tucson AZ


Collisions have played an important role in creating and sculpting the 
population of trans-Neptunian objects (TNOs).  In the earliest stages, 
low-velocity collisions led to the accretion of large TNOs from a population 
of small planetesimals.  Work on this subject [eg. 1-4] suggests that the 
primordial TNO population must have been substantially more massive than it 
currently is in order for large bodies like Pluto to accrete within the age 
of the Solar System.  Following the accretion and dynamical excitation of 
TNOs, more energetic collisions could have played a role in reducing the mass 
of the TNO population to its current level, and that collisional activity 
could be responsible for shaping the current size distribution of TNOs 
[eg. 1,5-10].  In addition, it has been suggested that collisional effects 
may be responsible, at least in part, for the differences between the colors 
of low- and high-inclination Kuiper belt objects [eg. 11-14].  Most work on 
these subjects assumes that the TNO population formed in its current location.  
Recent dynamical models [eg. 15] suggests that those bodies instead formed closer 
to the Sun and were pushed-out to their present locations during the migration 
of the outer planets.  In such a scenario, dynamical depletion dominates over 
collisional grinding as a mass-loss mechanism, although collisional evolution 
could still play an important role in the sculpting of the TNO size and color 
distributions.  A full understanding of the collisional evolution of the 
trans-Neptunian population thus requires consideration of its dynamical 
evolution as well.

This review talk will summarize the work to date on the collisional evolution 
of the TNO population and highlight the outstanding questions and uncertainties 
that remain, with a specific focus on the implications of different dynamical 
models [eg. 15,16] for the collisional history of the TNO population.  In 
addition, I will discuss the observational constraints that can be placed on 
the collisional history of TNOs, namely observational surveys that can constrain 
its current size and color distributions [eg. 17,18,11], and experimental 
constraints on the impact strength of TNOs [eg. 19-22], which is a necessary 
input parameter for any collisional modeling.


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