Scientists have developed tiny, lightweight devices that can float in the upper atmosphere using only the power of sunlight. These devices, made of thin sheets of aluminum oxide and chromium, take advantage of a phenomenon called photophoresis. This effect occurs when one side of a thin material gets warmer than the other, causing gas molecules to bounce off the warmer side and push the device upward.
In a recent experiment, researchers made small specks, about 0.4 inches wide, float in a vacuum chamber when exposed to light about 55% as intense as natural sunlight. Ben Schafer, lead author of the paper and a researcher at the Harvard John A. Paulson School of Engineering and Applied Sciences, said, “That’s a big result showing that this would actually work in the same conditions that you have in the upper atmosphere.”
The devices aim to explore a region of the atmosphere sometimes called the “ignorosphere” because there is little we can currently send there to gather data.
Devices exploring the upper atmosphere
This region includes the mesosphere, located between 30 and 53 miles above Earth, and a section of the thermosphere up to 100 miles high. Accurate data from this region about winds, temperatures, and pressures could improve the accuracy of existing global climate models.
Schafer and his colleague Angela Feldhaus have started a company called Rarefied Technologies to conduct realistic atmospheric experiments with these devices in the hope of commercializing them. To lift miniature sensors and antennae into the ignorosphere, the membranes would need to be around 2.4 inches wide. Schafer said, “It would be a disc that could loft about 10 milligrams into near space.” The devices would be released from a stratospheric balloon about 30 miles above Earth and self-propel to altitudes of up to 60 miles.
David Keith, a professor at the University of Chicago who suggested using reflective membranes powered by photophoresis for geoengineering, said, “This is the first time anyone has shown that you can build larger photophoretic structures and actually make them fly in the atmosphere. It opens up an entirely new class of device: one that’s passive, sunlight-powered, and uniquely suited to explore our upper atmosphere.”
This type of research could transform our understanding of the upper atmosphere and enhance our ability to predict and respond to space weather threats, ultimately protecting Earth’s technology and infrastructure.