How do scientists work out how the inside of a planet is structured, it’s size, density and temperature, and how much

Question: How do scientists work out how the inside of a planet is structured, it's size, density and temperature, and how much do we know about the structure of other planets?
- Keywords:
  planet,
  space
Asked by soggysheepy to Ravi on 20 Jun 2013.
- Ravi Kopparapu answered on 20 Jun 2013:
  
  A very excellent question:
  In the case of the Earth, we know of its structure, size and density through various measurements of rock samples, radar telemetry and measurements across the globe. But to do that on other planets, it is difficult. So based on radar measurements of spacecrafts and from Earth, we can find out the composition and temperature of those planets.

Question: How do scientists work out how the inside of a planet is structured, it's size, density and temperature, and how much do we know about the structure of other planets?