Sulfur was fingered long ago as an element that could be keeping Mercury’s iron core partly molten, much like salt on a snowy driveway lowers the melting point of ice, turning it liquid even in temperatures below 0°C.
Messenger is due back at Mercury in October. After a third flyby in 2009, the probe is scheduled to settle into orbit in March 2011 for a year-long, detailed study.
With regard to whether Mercury’s core is snowing iron, McNutt says the probe should be able to provide detailed maps of Mercury’s magnetic field, as well as chemical studies to identify sulfur and sulfur-rich deposits on the planet’s surface.
"Trying to understand globally how much sulfur we’re seeing might be important," McNutt says.
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 are typically caused by what is known as the dynamo effect, which happens when a conductive molten core rotates.
But most of the dynamo models 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.
They say 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 analysed.
The results were then applied to how the process would work on Mercury.