How can you tell a planet's composition?

Answer 1

The density can be computed from the volume and gravitational pull (mass). This will usually indicate the types of elements and compounds that make up the planet. The magnetic field gives a clue to the type of core.

Answer 2

A planet's composition can be determined through a variety of methods, such as analyzing its spectra to identify the presence of specific elements and compounds, studying its density and mass to infer its overall composition, and examining its surface features or atmosphere for clues about its makeup. Remote sensing techniques, like spectroscopy and imaging, are commonly used to study a planet's composition without directly visiting it.