The Planet Quiz Show  

Answer:   Mercury, Venus, Earth, and Mars

These planets are often referred to as the terrestrial planets because they are similar to the Earth. The four innermost planets have hard and rocky surfaces with dense iron-rich cores.

[The Hard and Rocky Planets]
The first four planets of our solar system are the hard and rocky planets. Here they are drawn to their correct sizes to each other and the sun, but not placed at their correct distances from the sun. Drawing by the International Astronomical Union...

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