Misunderstood “photophoresis” effect could loft metal sheets to exosphere

The Crookes radiometer, a device familiar to many, often sparks curiosity but is frequently misunderstood in terms of its underlying physics. When exposed to light, the radiometer's blades begin to spin, a phenomenon driven by forces known as photophoresis. Recent research has unveiled a groundbreaking application of this effect, suggesting that it could be harnessed to lift thin metal sheets into the upper atmosphere of Earth and other planets. This innovative approach aims to create a method for sending probes to altitudes that are too high for traditional balloons yet too low for satellites. Preliminary tests of working prototypes have been conducted closer to the Earth's surface, yielding promising results. There is a common misconception that the spinning motion of the Crookes radiometer is solely due to radiation pressure, where the darker sides of the blades supposedly absorb more photons, leading to a directional push. However, this explanation is flawed. In reality, the mechanics of the radiometer involve the interaction of light with both the dark and silvery sides of the blades. Photons bouncing off the reflective side contribute additional momentum, complicating the narrative around radiation pressure. The true operation of the device hinges on the temperature differential created between the warm, light-absorbing dark side and the cooler silvered side, which is crucial to understanding the photophoresis effect. This research not only clarifies longstanding misconceptions but also opens the door to exciting possibilities in atmospheric exploration.