QUESTION:
Was it a conscious decision to land on Mars on Independence day? If so, why?
Did it have anything to do with the film (or vice versa)?

ANSWER from Pieter Kallemeyn on July 28, 1997:
The real reason for landing on July 4th was due to the relative positions of
Earth and Mars in their orbits and the type of launch vehicle used to get us
there.  The fact that it just happened to be July 4th was more of a
coincidence than a conscious decision.

Pieter Kallemeyn