1) We spot exoplanets by their influence on the star, which is nearly nil at distances of 100+ AU. 2) We spot exoplanets that have huge volumes and masses, lik

1) We spot exoplanets by their influence on the star, which is nearly nil at distances of 100+ AU. 2) We spot exoplanets that have huge volumes and masses, like Neptune or Jupiter size (15x or 100x Earth's mass, or even multiples of Jupiter), but the ones we're talking about beyond the Kuiper belt might be on the order of 0.1 Earth mass or smaller. 3) 20M light years is an exaggeration, most detected planets are within 1000 light years.