High above our heads, between 50 and 100 kilometers (30–60 miles) above the Earth’s surface, lies the mesosphere—a part of the atmosphere that remains largely uncharted.
This region is too high for airplanes and weather balloons to reach, yet too low for satellites to orbit.
Scientists have long wanted to explore it, since data from the mesosphere could improve weather forecasts and climate change models.
But until now, we’ve had no reliable way to get there.
A new study published in Nature offers a promising solution: ultra-light floating structures that can rise into the mesosphere using nothing but sunlight.
The research was led by scientists from Harvard University’s John A. Paulson School of Engineering and Applied Sciences (SEAS), the University of Chicago, and other collaborators.
The technology relies on a physical phenomenon called photophoresis. This occurs when gas molecules bounce off the warm side of an object with more force than they bounce off the cooler side, creating lift.
Photophoresis only works in very low-pressure conditions—exactly the kind found in the mesosphere.
The research team built wafer-thin membranes made of ceramic alumina, coating the underside with chromium to absorb sunlight. When sunlight hits the material, the temperature difference between the top and bottom surfaces generates a lifting force strong enough to overcome the structure’s weight.
“This effect is usually so tiny you never notice it,” explained lead author Ben Schafer, who worked on the project as a Harvard graduate student. “But by making our structures extremely lightweight, the photophoretic force becomes greater than their weight—so they fly.”
The idea of using photophoresis for flight dates back more than a decade, when co-author David Keith proposed it as a possible climate engineering tool. Schafer began working on it alongside Keith and materials engineering expert Joost Vlassak.
Recent advances in nanofabrication finally made it possible to build such low-mass devices with high precision.
Using these techniques, the team created centimeter-scale flyers and tested them in a custom-built low-pressure chamber. They measured the photophoretic forces directly and compared the results with models of how the structures would behave in the upper atmosphere.
One experiment demonstrated a 1-centimeter-wide flyer levitating at an air pressure of 26.7 Pascals—similar to conditions found 60 kilometers up—using light at just over half the intensity of sunlight.
“This is the first time anyone has built larger photophoresis structures and actually made them fly in the atmosphere,” said Keith. “It opens the door to a new class of devices that are passive, sunlight-powered, and perfect for exploring the upper atmosphere.”
The potential applications are wide-ranging. If equipped with tiny sensors, these flyers could collect vital measurements—like wind speed, temperature, and pressure—from a part of the atmosphere that’s been a blind spot for scientists. This data could help improve climate models and weather predictions.
They could also be used for communications, creating floating networks of antennas capable of transmitting data like low-orbit satellites but with less signal delay due to their proximity to Earth. And because Mars’s thin atmosphere is similar to our mesosphere, the devices could be adapted for planetary exploration and communication there.
The next step is to add lightweight communications equipment so the flyers can send back real-time data during flight. Schafer says it’s exciting to explore a part of the atmosphere where “nothing could sustainably fly before—it’s like the Wild West for applied physics.”
The project has already inspired a Harvard spinoff company, Rarefied Technologies, founded by Schafer and Angela Feldhaus in 2024, to develop the technology further.
