We just don't know enough about the Comet Threat

A recent article in science magazine (http://www.sciencemag.org/cgi/content/summary/325/5945/1211)suggests there is still a lot to learn about cometary object distributions. Author Martin Duncan states:

Simulations show that the inner Oort Cloud is the source of many more long-period comets

than expected.

The inner Oort Cloud was not previously thought to produce many LPCs, for the following

reason...The object might have spent most of its life in the inner cloud and very recently been nudged into its current (large aphelion) orbit by weak planetary perturbations when its perihelion was drawn in to just beyond the orbit of Saturn (see the fi gure). The simulations of Kaib and Quinn show that a large fraction of the LPCs are generated via this mechanism.

The results of these simulations not only change our view of where the progenitors of

LPCs are stored but may also provide constraints on models of planet formation and on

the properties of the stellar nursery in which the Sun spent its formative years