The impactor and NEO orbit distributions have already been
discussed briefly above and in detail by Chesley and Spahr
(2004). The differences between the impactor population and the
fireballs are perhaps more interesting where it is important to keep
in mind that the comparison inFig. 1is between thebias corrected
impactor population and the observedbolide population. We believe that the apparent difference between the impactor and bolide
distributions is a consequence of the uncorrected observational
selection effects in the bolide data along with modifications in
the distributions due to the Yarkovsky effect (e.g.Farinella et al.,
1998). The bolide detection technique has a strong bias towards
high kinetic energy events that preferentially detects objects on
cometary-like orbits (Ceplecha et al., 1998). Indeed, if we consider
‘comets’ to be objects from our sporadic bolide data with a>4AU
ore> 0.9 ori>90then13.4% of the objects are of ‘cometary’ origin. This value is about twice the cometary fraction of 6 ± 4% suggested by the Bottke NEO model and consistent with the expected
‘comet’ enhancement in the bolide data. On the other hand, it is
only half the 25% cometary contribution suggested byStuart and
Binzel (2004).