Plasma Kristall-4 studies the interaction between atoms by recreating them on a larger scale, substituting microscopic dust particles and injecting them into neon and argon gas to watch their behavior – research impossible within Earth's gravity. Such “dusty plasma” tests constitute the longest-running series of experiments in the history of human spaceflight, as PK-4 is successor to the first natural-science experiment performed on the International Space Station in 2001, and is a project of the European, Russian and German space agencies, with support from NASA and the National Science Foundation.
