Steven L. wrote:

The "When Worlds Collide" scenario isn't impossible.

Actually, the one shown in the film is... figure out the velocity that
Bellus would have to have to get from first detection to Earth impact as
fast as is shown in the film - to get to Zira, the Space Ark must match
the velocity of the Bellus-Zira system as it passes by, and that's way
outside of the abilities of the propulsion technology shown in the film.

Pat