When we talk about systems with more than two bodies, we have to bear in mind the Principle of superposition of forces: the force exerted by one body on another is independent of that exerted by the rest.
In the solar system, with one star which accounts for almost all the mass, in many cases it is possible to ignore the forces among the planets. However, in this simulation these forces cannot be ignored: an asteroid with a small mass is moving between the sun and a large planet, Jupiter for example.