Question

What are the two main differences between extrasolar planetary systems discovered to date and our Solar System?

Answer 1

The biggest single difference is the small number of planets in extra-solar systems. The second is that very few of them are in a life-supporting zone.

Explanation:

The interest in planetary systems is about the possibilities of colonization, or even the development of other life forms beyond what we know of on earth.

HAVING planets is a first step, and so far the systems detected do not have very many. The second step is for a planet to be in an energy zone that can support life (as we know it). So far, Earth is the only one!