Near the point where the atmosphere bleeds into space, there is an unexplored zone known as the mesosphere or more colloquially the ignorosphere. Up there the air is too thin to support planes or balloons. Nevertheless, there is still enough material to burn up any satellite that ventures too low. Scientists hope to study the mesosphere using exceptionally light flying disks (best not to call them saucers), and have now demonstrated models of the idea in the lab.
The mesosphere is not quite a place “no one has gone before”, since every astronaut has passed through it both on the way up and down. The problem for those wishing to study its mysteries, including any influence on the climate below, is such passages have always been made very, very quickly, with no opportunity to stop and explore.
University of Pennsylvania graduate student Mohsen Azadi hopes to change that with research reported in Science Advances. Azadi and colleagues built a “light field” shining into a chamber where air can be evacuated to simulate conditions at 50-80 kilometers altitude (10-30 Pa or 0.0001-0.0003 times pressure at sea level). They then made 500-nanometer thick mylar disks (~1/50th of a human hair), and coated the bottom with carbon nanotubes. When placed in the chamber and exposed to the equivalent of sunlight, the disks warmed to around 100 K above the sparse air.
A molecule of gas encountering the disk from below interacted with the highly structured nanotubes many times, like a ball thrown into a corner where walls and floor meet. On the top side, a molecule would have only a single contact with the mylar. Consequently, once warm the lower surface imparted considerable energy to gas particles that struck it, causing them to recoil and provide an upward force on the disk. The mylar top layer gave much less energy to anything on that side, creating a net upward force on the disk. In other words, the light levitated them.
Sunlight alone heats the disks sufficiently to create an effect strong enough to balance the force of gravity on the disks’ tiny weight. Azadi and co-authors report it should even be possible to guide the disks by controlling their curl.
Although the disks need to be exceptionally light for the whole thing to work Azadi predicts even in their current 6-millimeter (0.24-inch) diameter format they can carry payloads of up to 10 milligrams. Tiny as this is, it could be enough to suspend a dust sensor beneath them, increasing their stability and revealing the mesosphere’s composition. Radar tracking of the disks could help us understand wind patterns at this height, something currently lacking from global climate models.
Research could even continue at night, with the disks heated by shining lasers on them, giving a whole new meaning to “Beam me up, Scotty.”
