Earth’s neighbors Mars and Venus both lack magnetic fields, indicating that their internal dynamos stopped functioning in the distant past. Surprisingly, however, the MESSENGER mission found that tiny Mercury still has a remnant magnetic field, even after 3.9 billion years. New research by a team of mineral physicists led by Geeth Manthilake of Clermont Auvergne University shows how Mercury could sustain an internal dynamo for that long without losing enough heat to space to solidify its core.

Manthilake and colleagues determined that the electrical and thermal conductivities of certain iron-sulfide alloys are much lower than previously thought, meaning heat does not pass through these alloys as quickly as through other components of the core. The team used X-ray diffraction methods on samples of iron-sulfide at high temperatures to obtain new conductivity data. They attribute previous results to the unintended inclusion of oxygen in prior experiments. The alloys studied are buoyant within the metallic liquid of the core, allowing them to float to its top. Once there, their low thermal conductivity would effectively act like a blanket, preventing heat from escaping efficiently and slowing the solidification of the core — perhaps enough to maintain a dynamo until the present day. READ MORE