Answer: by using the world's most powerful laser
Scientists believe that the unique atmospheric conditions of the planet Neptune cause it to rain diamonds there, and they’ve just put this theory to the test. Using the Stanford Linear Accelerator Center (SLAC) Laboratory, a research team successfully re-created the methane-rich conditions of the gas giant and created diamond rain.
They did so by subjecting a plastic material called polystyrene to high pressures using SLAC’s Matter in Extreme Conditions (MEC) component of the Linac Coherent Light Source (LCLS). Also known as the most powerful laser in the world, the MEC created shockwaves in the plastic that turned the carbon atoms inside it into diamonds just a few nanometers in size.
While the diamond raindrops created in SLAC are much, much smaller than those that fall on Neptune, this technology could be used to create nanodiamonds for commercial purposes in the future. And scientists are now one step closer to uncovering the many secrets of that distant planet in our solar system.