The diameter of Venus is just 650 km less than the Earth’s, and its mass is 81.5% of planet Earth.
Looking inside Venus is much harder. Here on Earth, scientists probe the structure of the Earth’s core by studying how seismic waves from earthquakes bounce off the interior of the planet. Only a few landers have reached the surface of Venus, and they didn’t last long.
Since Earth and Venus have similar size and density, scientists assume that Venus has a similar internal structure to Venus, with a core, mantle, and crust. The interior of Venus is probably at least partially liquid.
One big difference between Earth and Venus; however, is the fact that Venus has no plate tectonics. This is probably because the surface and atmosphere of Venus are so dry and hot. This reduces the amount of heat lost from the interior of the planet, and prevents it from cooling. This might also explain why Venus doesn’t have an internally magnetic field; such as the one generated by Earth.