Astronomers have only found 250 extra-solar planets, so this conclusion might still be premature…
but early signs point to our solar system being of a fairly rare kind.
First, a brief description of ours: we have a few small rocky planets near the sun (Earth, Mars, Mercury, Neptune) surrounded by “big gas giant” planets like Jupiter and Saturn. These big planets have strong gravitational pull and “sweep” away everything they encounter, such as big asteroids and even smaller rocky planets that don’t stay away. Essentially, the gas giants protect the smaller inner planets from garbage. (not perfectly, of course.)
However, it appears that in many, if not most, of the other solar systems in our galaxy, the big planets are nearer to the sun. So if there was a earth-like rocky planet near the star, it has long ago been eaten by a big giant. Any earth-sized rocky planets far from the star would be pummeled regularly by big asteroids and other galactic junk.
So, it might be harder to find our alien friends than originally hoped. 
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