Plasma Kristall-4 proxy atoms

Shear flow motion in a complex plasma fluid in weightlessness on the International Space Station. This image is part of the Plasma Kristall-4 experiment.

Plasma Kristall-4 is an International Space Station experiment that injects microscopic dust particles into a neon or argon tube to act as atom substitutes. As they float in the charged gas, they will collect negative charges as positive ions accumulate around them. As a result, they will start to repulse each other – just like atoms do in a fluid state.

Particle flow is induced through the radiation pressure from a laser beam aimed at the central part of the particle cloud.

This manipulation causes the proxy atoms to interact strongly, leading sometimes to melting. The particles in PK-4 are made of plastic.

A plasma is an electrically charged gas, a bit like lightning, that rarely occurs on Earth. It is considered to be the fourth state of matter, distinct from gas, liquid and solid matter.