How is it that small rocky planets such as Mercury or Ganymede, one of Jupiter’s moons, have a magnetic field? It could be due to to “snow” made up of flakes of iron. In the interior of these planets, the flakes, falling from the outer reaches of the liquid core to its centre, could cause turbulence that might potentially generate a magnetic field. To investigate this process, the researchers modelled iron snow in a tank of stratified salt water using glass beads – as fine as flour – to which they added an orange dye. Initially, a few large flakes fall out of the cloud at high speed. But, as time goes by, billions of small ones slowly fall in continuous streams. The sinking of the dye reflects the
impact of snow flakes on their environment. This image is one of the winners of the 2022 La preuve par l’image (LPPI) photography competition.