Curiosity › Science › Physics › How can NASA tell exactly what an exoplanet’s is made up of? › Reply To: How can NASA tell exactly what an exoplanet’s is made up of?
It is called spectroscopy. All objects in this universe give out a spectrum of light. On Earth, we have analyzed and categorized all such spectrum for different chemical elements. Astronomers analyze the spectrum of the planet to decide what the planet is made of.