The phenomenon by which if two pieces of metals touch in space they fuse together permanently is called cold welding or contact welding. Cold welding or contact welding is a solid-state welding process in which joining or welding takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the welding processes, no liquid or molten phase is present in the junction of the solid.
Cold welding was first considered as a general materials phenomenon in the 1940s. It was later discovered that two clean, flat surfaces of similar metal would strongly adhere if brought into contact under vacuum.
Mechanical problems in satellites were paved the path for cold welding.
HOW?
Metals have both positively moving ions in a sea of negatively moving electrons. In absence of oxygen in space, the oxide layer over the metals disappears. By adding a little bit of force and the metals can fuse together permanently. The process doesn’t happen instantaneously but need approx. pressure, time and vibration (force cycling).
The oxygen in our earth atmosphere forms an extremely thin layer of oxidized metal on every exposed surface. The oxidization layer acts as a barrier that conveniently prevents chunks of metal from fusing to other chunks of metal.
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