system
Given the following post, respond as if you're commenting on Reddit:
human
How do Astronomers figure out what the interior of planetary bodies are made of without sending probes there? (Neptune, Uranus, Ceres, etc)
gpt
1. A general idea of the composition of our solar system

2. Specific measurements of the objects gravitational effects

3. Spectrographic analysis of the surface or surface clouds

Taking 1 + 2 + 3 what "mix" best results in that density at that size as best we understand the physics.