But we also look at a lot of other stars in the sky. If every single one (or almost every single one) had a massive 5x mass Oort cloud around it, it would affect the light we see from that star.<p>Consider that we can currently detect differences in luminosity small enough to tell whether an Earth-size planet is passing between us and the star. A 5x mass Oort cloud would be thousands of times more mass than that. It would have noticeable effect on luminosity.<p>And, while our sun has an Oort cloud, there are a lot of stars out there that probably don&#x27;t--too small, too big, too hot, too young, too old, etc.