Researchers at the Nankai University in China noticed that when cutting a graphene sponge (a sponge-like material made by fusing crumpled sheets of graphene oxide) with a laser, the light propelled the material forwards. While lasers have been previously used to move single molecules around, the sponge was a few centimeters across and presumably too large to move.

The scientists then placed pieces of graphene sponge in a vacuum and shot them with lasers of different wavelength and intensity. They managed to push sponge pieces upwards by as much as 40 centimeters. They even got the graphene to move by focusing sunlight on it with a lens.

Speculating on how the movement was occurring, several theories were ruled out and the scientists believe that the graphene absorbs laser energy and builds up a charge of electrons. Eventually it can't hold any more, and extra electrons are released, pushing the sponge in the opposite direction. Although it is unclear why the electrons do not fly off randomly, the team was able to confirm a current flowing away from the graphene as it was exposed to a laser, suggesting this hypothesis is correct.

This discovery sparked the imagination of the scientists, who now contemplate using graphene sponge to make a light-powered propulsion system for spacecraft that would beat solar sails. Such a spacecraft would not require fuel to move forward, which is of course an appealing idea, but even if the technology could be achieved, one of the problems that may occur is that the loss of electrons would mean the craft builds up a positive charge that would need to be neutralized, or it could cause damage.

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