The control specimen — the only world in this atlas we can check in person, and the reference every other one is measured against.
Every instrument flown to another planet was calibrated here first. When we say Venus is Earth-sized or Mars once had water like ours, this is the 'ours' — the one world where the ground truth is literal.
It is also the only planet whose surface is mostly invisible in its own map: two-thirds ocean floor, mapped more coarsely than the face of Mars.
Inner coreSolid iron-nickel
Outer coreLiquid iron — the dynamo behind the magnetic field
MantleSilicate rock, slowly convecting
