Dust grains tend to emit radio signals with wavelengths around their own size. This fact allows us to study the types of dust being formed in early planetary systems.
Gravel Road
We have a pretty good idea of how planets form around stars. We know that dust is formed from the remnants of supernovae, that protoplanetary disks of dust form around young stars, and that dust grains can clump together to form pebbles. We also know how larger planetoids can drive the formation of planets, and how planets can migrate from their point of origin to their stable orbits. But there are still gaps in our understanding.
Interstellar
Earth gets bombarded from space all the time. With all the micrometeorites, not to mention the occasional meteor or comet, almost 50 tons of material falls to Earth every day. Since all this material from space reaches Earth, you might think that interstellar material falls to our planet all the time. But it turns out that isn’t the case. The vast majority of material comes from within our solar system. Even cometary material comes from the Oort cloud at best, and that’s still on the outer edge of our solar system. There is plenty of interstellar gas and dust beyond our solar system, but even when some of it heads our way it tends to be pushed away from the inner solar system by the solar wind. So we haven’t had any samples of interstellar dust to study.
Dust to Dust
We are the dust of stars, as Carl Sagan so famously said. The elements in our bodies (with the exception of hydrogen) were formed within stars, and then cast out to the universe when large stars explode as supernovae. Of course simply creating elements by nuclear fusion and sending them flying into the cosmos isn’t quite enough to make stardust. The elements also have to clump into dust particulates. Understanding that process has posed a bit of a challenge, but now a new paper in Nature has observed it happening in real time.