Prior remnant

Mercury

A core with almost no coat left

Most of the planet is core. It has shrunk. Ice hides in polar dark. The last ash of a finished world, or a stripped first-generation body.

What the cameras and papers show

Mercury’s core occupies most of its volume — a much larger iron fraction than Earth’s. The planet is locked in a 3:2 spin–orbit rhythm. Global contraction is recorded in long cliffs that wrinkle the crust.

MESSENGER found unexpected volatiles and confirmed water ice in permanently dark polar craters. The Caloris basin is one of the largest impact scars in the inner system.

BepiColombo is approaching Mercury and will weigh that interior again.

How this site reads it

In this project Mercury is not the first small world. It is what remains after a cycle has run past Venus.

A large core can also be a first-generation body that lost its outer rock in a giant impact. That textbook story is granted first. The remnant reading has to survive it.

What would kill this stage

If Mercury was always small and mostly iron from the start, the remnant reading comes off the table.