ATMOSPHERIC SCIENCE: Ignorosphere Surfers

SCIENTISTS HAVE DEVISED tiny featherweight disks that could float freely in Earth's mesosphere or the thin air of Mars, theoretically even while carrying payloads.

-  -Payal Dhar

Our mesosphere, which extends about 50 to 85 kilometers above the planet's surface, is sometimes called the "ignorosphere"-it's too high for aircraft and weather balloons to reach but too low for access by satellites, making it one of Earth's least-studied regions. Versions of the researchers' light-powered fliers could potentially carry sensors through this zone.

The new centimeter-wide prototype disks are made from two thin, perforated membranes of aluminum oxide connected by minuscule vertical supports.

They are kept aloft by a force called photophoresis: the light-induced movement of small particles at very low atmospheric pressures. In laboratory experiments described in Nature simulating mesospheric air pressure and illumination, the researchers showed that their devices could float passively without any power source.