Collect some silicate rocks and determine the density. Core Iron, nickel metal Same, but core is much smaller. Sediment or Regolith Silicon and oxygen bound in minerals that contain water, plus organic materials. No water or organic materials. Some carbon gases, but very little of them.
Pressure is about one-trillionth of Earth's atmospheric pressure.
Ocean floor characterized by mountains, plains, and trenches. 84 percent heavily-cratered highlands. 16 percent basalt-covered maria. Numerous impact craters - some with bright rays, crater chains, and rilles. Compare maps of Earth and the Moon.