re: NASA: new solar system , Trappist-1 ,where life may have evolved on 3 planets

quote:

---

They can detect the dimming of the Star as the planet passes in front of it and also detect what they call the "wooble." Which is the star itself actually shifting left and right due to the planets gravity.

---

That part I understand, but I still don't understand how they can get any information on the planet aside from its size and density. I don't understand how looking at our own solar system from 40 light years away that you could tell much of a difference between Earth and Venus.