Iron snow – such a phenomenon may occur in some corners of the solar system. Research by scientists from the United States indicates that it occurs not on the surface, but in the cores of some small planets and large moons. This may happen, for example, on Mercury or Ganymede.
Winter has arrived in our part of Europe, and many cities are covered with a layer of snow and ice. On Earth, it is formed by water crystals, but this is not the case on all celestial bodies – for example, on Mars there is precipitation of frozen carbon dioxide. As a study published in the journal “Geophysical Research Letters” shows, unusual “snow” may occur not only on the surface.
Snow and the magnetic field
On Earth, snow is formed when water crystals fall from the upper layers of the atmosphere to the lower ones, where they melt. A similar thing happens with iron crystals inside some planets. Near the boundary of the core and mantle, iron cools and forms crystals that fall down into the core, where they melt again.
The researchers drew these conclusions based on laboratory experiments with a bottom-cooled column containing water – in which the situation was reversed. When the lower layer of fresh water froze, crystals formed in it and rose up, where they melted and returned down as warmer water. Eventually, the returning, warmer water heated the lower layers so much that the entire process stopped. Then it would cool down again and movement would start again.
The researchers compared these results to theoretical models of planets and concluded that a similar phenomenon should occur in iron planetary and lunar cores. The described movement should cause the cyclical creation and disappearance of magnetic fields of some small planets, such as Mercury, as well as moons, including Ganymede – the largest moon of Jupiter. The authors plan to further study “iron snow” on how its particles move inside the core and what degree of subcooling is necessary for the formation of crystals.
Main photo source: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington