> However, the design can be miniaturized, and the researchers built a version that weighs only 9 milligrams.
Ars A/B tests their titles so I don't know if the submitter editorialized or if they saw a different title than the rest of us, but the text of the article does include building a 9 mg version.
A/B test or not, 9mg is impossible. That would be half the mass on a grain of salt.
At those length scales the interesting forces at play are not fluid mechanics, but capillary forces and surface tension. It also trivially easy to make - just rip a piece of gold foil weighing 9mg
A mosquito weighs 2.5 milligrams. It also has almost exactly the same hovering power to weight ratio. At 8mm high it is indeed a very tiny "drone", and exceedingly fragile, but it is certainly not impossible.
Ars A/B tests their titles so I don't know if the submitter editorialized or if they saw a different title than the rest of us, but the text of the article does include building a 9 mg version.