How do the scientists know what the core of other planets are made of, (eg: Mars’ core is iron, Neptune’s liquid diamond) even though mankind has never been there?

Question

How do the scientists know what the core of other planets are made of, (eg: Mars’ core is iron, Neptune’s liquid diamond) even though mankind has never been there?

In: Other

Answer 1

Astronomers have telescopes that can photograph the planets and other objects under different spectrums of light, such as X-ray, gamma rays, and ultra-violet. Each mineral reacts to light differently and we can deduce the composition of something from far away without having to sample it firsthand.

Edit: I’m not an expert. And apparently this is just how they detect atmospheres of objects in space. My bad.