So what can this unusual library tell us? First, there is the simple parts list. The most common component was organic material, present in 40 of the 63 particles – exactly what is unclear, but it could be anything from pollen to sloughed-off bits of researcher. Quartz, found in 34 particles, came next, followed by carbonates (17 particles) and gypsum (14). “The minerals blow in,” says Coe. “They come from all over the world.” Other ingredients included air pollutants and fertiliser chemicals.
Anyone counting will also have noticed that there are already more components than particles. That is because most specks of dust are conglomerates, which means they may take an infinite variety of forms, much like snowflakes. The next obvious step was to find out what individual conglomerates looked like, but pinpointing exactly which speck corresponded to which spectrum wasn’t going to be easy. So Coe launched a competition. The first person to capture an electron microscope image of a particle that had already been analysed with infrared light would get to name it. And, if that was not enough, there was a free dinner on offer too. What student could fail to rise to that challenge?