February 2014 the Kepler Science Team announced the discovery of 715 new planets outside of our solar system.
How do we know that it’s a planet and not something else in the way? We keep watching. If we see the same star, dim by the same amount, for the same amount of time in the future; we know we have a planet.
So if you think about it, scientists look for planets outside of our solar system, not by what we see, but by what we don’t see. When the Kepler team are convicted that what they have NOT seen is a planet, they announce it.