Smallest Planet Yields Big Surprises
Mercury is even weirder than expected, NASA’s MESSENGER probe is showing. For starters, the planet’s interior is built differently than anything else scientists have blueprints for. Unlike Earth’s, Mercury’s core — which gobbles up 85 percent of the planet’s radius — consists of three layers instead of two. At the planet’s heart lies a probable solid layer, surrounded by a swirling liquid iron layer, all encapsulated by a third, solid iron-sulfur layer.
Reconciling Mercury’s surface composition with its density has confounded scientists until now. Surface rocks don’t contain enough heavy elements, like iron or titanium, to account for the observed density when a standard, two-layered core is considered.