One minor goof with this episode: to the aliens on the surface of the planet, the comet would not be seen tracking across their sky if it was on a collision course. An object on a collision course visually appears to have 'zero bearing drift with decreasing range.' It would simply hang in the sky, getting bigger over days and months, until the very end when it hit atmo and might be seen passing overhead on its way to the impact point. This was something that the movie "Deep Impact" actually got right.
Very minor nitpick, and it didn't detract from my enjoyment of the ep at all. I was more bothered by the size of the captain's cabin.