Flakes of iron snow could be falling inside the planet Mercury, according to a new experiment. This hot metal snowfall might help generate Mercury's puzzling magnetic field.
Researchers in the US have attempted to recreate the likely conditions within Mercury's liquid outer core, which is thought to be a mixture of iron and sulphur.
They used an arrangement of magnesium-oxide blocks, called a multi-anvil cell, to squeeze their iron and sulphur mixture to immense pressures, at temperatures above 2000 °Celsius. Iron crystals formed in the mixture.
"We saw iron crystals gathered at the bottom of the sample, while the liquid phase stayed on top," says team member Jie Li of the University of Illinois in Urbana-Champaign. Mercury's iron snow should form simple cubic crystals, rather than the intricate hexagonal patterns of water-ice snowflakes on Earth.
The detailed weather forecast for Mercury's interior depends on exactly how much sulphur is added to the mix. There may even be two layers of snow clouds, each slowly sprinkling iron crystals down onto the solid inner core.
This process is likely to affect patterns of convection in the core, and therefore the magnetic field.
In Earth's liquid iron outer core, convection currents generate our planet's relatively strong magnetic field in a process called the geodynamo. The mercurodynamo must work a little differently, as Mercury's field is probably less than 1% as strong as Earth's.
"No one knows how exactly this influences the magnetic field, but a snowing core is certainly different from the Earth's core," which is solid from the bottom up, Li told New Scientist.
Mercury's inner structure and the nature of its magnetic field should become clearer after NASA's Messenger mission arrives at the innermost planet in 2011.
Journal reference: Geophysical Research Letters (vol 35, page L07201)
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