Smallest Planet Yields Big Surprises
Mercury is even weirder than expected, NASAâ€™s MESSENGER probe is showing. For starters, the planetâ€™s interior is built differently than anything else scientists have blueprints for. Unlike Earthâ€™s, Mercuryâ€™s core â€” which gobbles up 85 percent of the planetâ€™s radius â€” consists of three layers instead of two. At the planetâ€™s heart lies a probable solid layer, surrounded by a swirling liquid iron layer, all encapsulated by a third, solid iron-sulfur layer.
Reconciling Mercuryâ€™s surface composition with its density has confounded scientists until now. Surface rocks donâ€™t contain enough heavy elements, like iron or titanium, to account for the observed density when a standard, two-layered core is considered.