There are several ways to simulate the high pressure, high temperature conditions of planetary interiors. I often use a small device called the diamond anvil cell. It uses two ~0.2 carat diamonds with sharp tips to squeeze a tiny sample, in order to generate pressures up to several million times of the ambient atomspheric pressure. Diamond is transparent to both visible light and X-ray. This feature allows us to heat the sample with laser, and to measure the properties of the sample in-situ using optical spectroscopy.