The Earth’s mesosphere is a “no-fly zone”. The air in this layer of the upper atmosphere is too thin to support aircraft. But new, light devices could defy that rule, requiring only sunlight to keep them aloft on high.

The technology is based on photophoresis, the flow of gas generated around an object when light shines on it. This effect is particularly strong at low pressures, as in the mesosphere (50-85 km above Earth. Aircraft designed to harness this principle levitated in laboratory conditions that mimicked the mesosphere, physicist Benjamin Schafer and colleagues reported. 

This could help scientists unlock the secrets of the mesosphere, which is so poorly understood it’s known as the “ignorosphere”. Just 1 cm wide, the fliers weigh less than 1 mg. Cradling one in your hand feels like holding nothing, says Schafer, of Harvard University and Rarefied Technologies.