NEO searching is sometimes framed in Rumsfeldian terms:
- Known knowns (NEOs we've found/tracked, plus asteroids and short period comets... tens of thousands of objects)
- Known unknowns (NEOs we think exist but haven't found/tracked, plus asteroids, short and long period comets... hundreds of thousands of objects)
- Unknown unknowns (Dark comets? Hypervelocity fragments? Rogue Star?... ???)
and similar robotic surveys are logging new objects every night, but even if we had perfect observation, we still wouldn't account for everything.
Add to that the fact that as a dynamic system, things change
and need recalculating of subsequent ripples and ricochet effects.
NASA maintains a Risk
page with details of quite a variety of objects (sortable)
As for the impact calculators... Old school
, or Twins