The collision of a micrometeoroid with a spacecraft. Micrometeoroids are small particles of dust weighing no more than a millionth of a gram. However, the particles can be dangerous, especially in great numbers, since they usually advance at high velocities. The Voyager probes were hit thousands of times by micro-meteoroids the size of smoke particles during their journey past the planets Jupiter, Saturn, Uranus, and Neptune. Spacecraft can be protected from these impacts by multi-layer, thermal insulation blankets made of strong fabrics such as Kevlar.