New measurements demonstrate that smoke particles in the upper atmosphere are twice the size of lower-altitude ones.
For decades, science fiction writers have tried their best to prepare us for eventual contact with aliens. Their efforts are dominated by several recurrent tropes. There's the invasion by a warlike species, there's the highly-evolved species trying to communicate with our primitive species, there's the benevolent aliens come to save us from ourselves, and there's the mischievous anal-probers and medical experimenters.

