Quick initial disclaimer that I’m not an astronomer, so I may be off on some of these points.
There’s more to it than just looking at dots/brightness—we also can look at what the specific light is. Different elements absorb/reflect different spectra of light. If you look at the “colors” of light you get back, you can match it up against combinations of elements to try to back calculate which elements comprise the planet. We can also do a similar method on stars to figure out what elements they’re comprised of, which helps inform their age, size, etc.
Edit: here’s a link to
a description with some imagesWe can also look at the timing of the light—if it’s a planet orbiting a star, the star’s light should dim at a specific amount on regular intervals as the planet passes in front of the star. Those intervals, the timing, and how much it dims let us calculate how long the orbit is, and also possibly how far from the star the planet is or how big the planet is.
There’s also ways to calculate distances to the system itself (and possibly within) using parallax, I’m not completely sure on the method but there’s tons of articles online.
Once you know how big the planet is, what it’s made of, how fast it orbits, how big the star is, etc etc, you can basically mock up the system in a computer model and figure out how it works. In something like this, scientists probably concluded that it wouldn’t be possible for the planet to be just a solid titanium ball, and instead silica/titanium clouds are more likely. There’s probably also differences in how the light is reflected between clouds and solids, which they can analyze.
And again this is just my understanding as a scientist that reads astronomy papers; my research is not at all in this so I’d love for corrections/additional insight from real astronomers