If there were no force acting on Mars, it would just move into space on a straight line.

Consider this example (with which I hope you are not personally familiar).

On an icy road, the net force on a car is very nearly zero.

ASTR 121 Home

ASTR 121 Home
Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA soper@bovine.uoregon.edu