Inside Mercury, Is It Snowing Iron?

May 8, 2008 -- Scientists have long wondered about how a planet as small as Mercury could have kept its iron core fluid enough to account for the planet's magnetic field. Physics would seem to dictate that the core cooled and solidified long ago.

Now researchers are chewing on another theory: It's snowing iron flakes inside Mercury.

The scenario opens new possibilities for explaining the planet's global magnetic field. Mercury is the only other terrestrial, or rocky-bodied, planet in the solar system besides Earth to have one.

Recent findings from the MESSENGER probe, which made its first pass by Mercury in January, verified that the planet's magnetic field is dipolar, meaning it has north and south polar orientations, like Earth's. Such fields typically are caused by what is known as the dynamo effect, which happens when a conductive molten core rotates.

Most of the dynamo models, however, predict fields thousands of times stronger than those existing on Mercury today. Researchers at the University of Illinois and Case Western Reserve University in Ohio may have found an explanation for the anomaly: A mix of iron and sulfur could be creating flakes of iron snow near the core's outer edge.

The scientists experimented with an iron-sulfur blend to simulate Mercury's core. The mix was compressed, heated, cooled and analyzed. The results were then applied to how the process would work on Mercury.