Researchers at Harvard's John A. Paulson School of Engineering and Applied Sciences (SEAS) have successfully demonstrated lightweight, solar-powered devices capable of sustained levitation within Earth's mesosphere. This innovation, detailed in the August 13, 2025, issue of Nature, utilizes the principle of photophoresis to explore a region of the atmosphere previously marked by significant data gaps. The mesosphere, located approximately 45 miles above Earth, is challenging to study due to its altitude, being too high for conventional aircraft and weather balloons, yet too low for satellites. This has led to it being dubbed the "ignorosphere." Traditional methods like sounding rockets offer only intermittent data, leaving much of this critical region unexplored. Understanding the mesosphere is vital for refining climate models and improving weather forecasting accuracy, as it influences global atmospheric circulation and other atmospheric layers.
The newly developed devices are constructed from thin, centimeter-scale membranes made of ceramic alumina, enhanced with a chromium layer to maximize sunlight absorption. When exposed to light at 55% of natural intensity in a vacuum chamber mimicking mesospheric conditions, these membranes levitate. This photophoretic propulsion, where light-induced heating of gas molecules imparts momentum and generates lift, has been a subject of scientific interest since the late 19th century. Recent advancements in nanofabrication have enabled the creation of structures so lightweight that the photophoretic force generated by sunlight is sufficient to overcome their weight. These devices, envisioned as swarms of low-power sensors, could continuously collect crucial data on wind speeds, temperatures, and pressures within the mesosphere, essential for calibrating and enhancing climate models. The research was led by Ben Schafer, in collaboration with Professor David Keith of the University of Chicago and Professor Joost Vlassak of SEAS. This work has also led to the creation of Rarefied Technologies, a startup founded in 2024 to commercialize this technology for real-world atmospheric experiments and applications.