Not the order from the Sun
The sequence
Eight worlds, a proposed start at Jupiter’s Great Red Spot, and two remnants. Look at each body first. Then as a stage.
Proposed beginning
Great Red Spot
Jupiter’s longest-lived large storm. If a new world is starting, it would sit under this weather, not in the clouds we can see.
Stage 1
Io
The most volcanic silicate world known. Almost no craters. Sulfur still paints the ground. The first visible rocky face in the sequence.
Stage 2
Europa
A global ocean under ice that is geologically young. The jump from dry Io to this much water is the first hard riddle of the sequence.
Stage 3
Ganymede
The largest moon in the solar system — bigger than Mercury. Layered inside. The only moon with a magnetic field of its own. Dark old land and younger grooved land.
Stage 4
Callisto
The outer Galilean world. Thick ice. A surface that has been largely still. The most cratered of Jupiter’s large moons.
Stage 5
Titan
The first world in the sequence with weather you could tell a child about. Nitrogen air. Methane rain. Lakes and seas.
Stage 6
Triton
Neptune’s large moon. It orbits the wrong way. Capture is granted. The leftover question is the body itself, not the frost on top.
Stage 7
Mars
A day like ours. A tilt like ours. Land of continental scale. Air that was once thicker. The last stop before a living Earth.
Stage 8
Earth
Oceans, breathable air, a biosphere. The only world we know that completed the sequence into a living planet.
Prior remnant
Venus
Earth-sized and spent. Ninety-two bars of carbon dioxide. A surface wiped a few hundred million years ago. Read as an ending, not a first draft.
Prior remnant
Mercury
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.