At the modest temperatures and pressures of Earth’s surface, the densest known material is the metallic element osmium, which packs 22 grams into 1 cubic centimetre, or more than 100 grams into a teaspoonful. Read here.

A new study disputes the prevailing hypothesis on why Mercury has a big core relative to its mantle. For decades, scientists argued that hit-and-run collisions blew away much of Mercury’s rocky mantle and left the big, dense, metal core inside. But new research reveals that collisions are not to blame — instead, the density, mass and iron content of a rocky planet’s core is influenced by its distance from the sun’s magnetic field. Read more