The planet's hot interior isn't where you'd expect to find snow, but scientists do suspect there's "iron snow" on Earth's core. Now, a new study simulates this dynamic in the laboratory and finds that iron snow may cause the magnetic fields of some planets to switch on and off.
Thousands of kilometers of rock separate us from the Earth's core, making it difficult to truly understand what's going on beneath it. To find out, scientists studied how seismic waves move through different strata. Changes in the speed of seismic waves reveal clues about what the different strata are made of.
These studies highlight some anomalies at the interface between the inner and outer cores. In 2019, a team of scientists proposed an explanation for these strange observations - that iron could crystallize near the mantle boundary and then settle like snow into the core.
In a new study, French scientists created a laboratory experiment that mimics the physics of how iron snow forms and flows to understand what might be happening inside a planet. The experiment replaced regular "iron snow" with a jar of water that was cooled from the bottom up, and added a layer of salt water at the bottom to prevent ice crystals from sticking.
The team found that as the lower water cooled, ice crystals formed, then floated upward, melting when they reached the warmer waters above the tank. The water flow stirred up by this process eventually warms the underlying water, temporarily preventing the formation of new ice crystals. This slowed the flow, allowing the water at the bottom to cool down, and soon new crystals formed and the process began again. The entire cycle lasted approximately 23.3 minutes.
Similar cycles may occur inside planets, but on a much larger scale, the team said. This would stir up the internal fluid flow of the molten iron and have an intriguing side effect - the strength of the planet's magnetic field would fluctuate so much that it would appear and disappear at periodic intervals.
This obviously won't happen on Earth, which has a strong magnetic field, but it could happen on objects with weaker magnetic fields, such as Mercury or Jupiter's moon Ganymede. There are more questions to be answered, but regardless, it's an intriguing idea.
The research was published in the journal Geophysical Research Letters.