It's called 'Physics'.
""The researchers, led by Dr Tinetti, found that the planet absorbs the starlight in a way that can only be explained if it has water vapour in its atmosphere."
Only be explained with current knowledge, but given we really have no direct observation of all these planets outside our solar system we really are clutching at straws based on the limited things we know about the universe.
Whilst these are the most likely explanations, I'd hardly say it's conclusive.
I'm not totally convinced these planets are actually 100% planets. They're just "probably planets based on what we know"."
One of my best friends worked on this project for years, he moved his wife and infant son to Paris to do so. He turned down lucrative offers domestically to move to a country where he didn't speak the language becuase his Ph.D allowed him to prove exactly this kind of thing.
We can say absolutely that the planet has water molecules on it due exaclty to DIRECT OBSERVATIONS and this IS conclusive. Based on what YOU know, they might not be planets, based on what SCIENCE knows, they are, peer-reviewed and triple-checked. Physics don't lie, they are the fundamental laws by which we navigate through our lives, on a Newtonian-scale, we understand the Laws of Nature quite well. It is only when things are very large or very small that we have to abstract them in order to begin to understand them.
Sure, I will conceed that the Flying Spaghetti Monster is manipulating our minds into thinking we are seeing water, but to what end? If we don't start cluthcing at straws, what is the point of life anyway? If the Church tells us how to live, where is the Free Will to sin in the first place?
There are many things that I, you and Science do not know. Knowing what we do not know is the difference between crackpot quasi-intellectual statements about Moonbeams and crystals and hard science.