On the surface of the Moon and asteroids, you can find pits smaller than a pinhead but with shiny, melted rims. Such marks are left by tiny meteorites, but the exact impact speed at which melting occurs remained unclear. To find out, researchers swapped the space rock for a laser: a short pulse heats a spot on the rock just like a fast dust grain would.
The laser allowed precise control of energy. The scientists zapped rock samples and measured the resulting pits. It turned out that the crater volume depends on the total pulse energy and on how much heat is conducted into the rock. From these data, they calculated the speed a real micrometeorite would have: between 100 and 1000 meters per second. For comparison, a bullet from a pistol travels three times faster.
These results also explain the wavy rims seen on some microcraters. They arise from an instability at the boundary between molten and solid material, like ripples on water when a gust of wind blows. Ripples like that need speeds of about 100 meters per second, which matches the experimental estimates.
Laser simulation of impacts offers a simple way to study the surface history of celestial bodies. Now, looking at a melted crater, you can estimate the speed of its maker, and whether it was a primary meteorite or a fragment from a larger impact.
Microcraters on the Moon are so small that they are studied under a microscope, but they can reveal the speeds of particles that flew billions of years ago.
In Arthur C. Clarke's novel "A Fall of Moondust," tiny particles on the Moon pose a danger to equipment — much like real micrometeorites that leave melted craters.