In Jack Higgins' readme file he mentions the xyz data he provides carries on further and that "we" could decide when and where to end the comets. Which is what I did with the first version. Unfortunately I was lazy and didn't write it for the older versions of Celestia so many people couldn't see the impacts unless they upgraded to a newer beta version. Glad to see it being improved upon and hope to see the impact points on the planet one day Really hope Celestia will allow true animations soon too! Would be so cool to position our "ship" near the impacts and see mushroom clouds.
By the way Rowan, I've replaced the impact code on my pc with yours, great work! You realize of course now you have to do more