Stage 6

Triton

A thin leftover sky

Neptune’s large moon. It orbits the wrong way. Capture is granted. The leftover question is the body itself, not the frost on top.

What the cameras and papers show

Triton is retrograde. That is why textbooks say captured, and this site grants the geometry.

Voyager 2 in 1989 found young patches, nitrogen geysers, a pink south cap, and a cantaloupe-textured terrain. Mean diameter is about 2,707 km — smaller than Europa, larger than Pluto.

Today the air is a thin nitrogen leftover, a small fraction of Earth’s. Models allow a thicker past atmosphere that later collapsed onto the ice.

No later mission has returned. A future Neptune encounter would weigh the body, not just the frost.

How this site reads it

This looks like a world after a thicker atmosphere: thin leftover air, young patches, nitrogen geysers.

The orbit the wrong way is granted as capture. The leftover question is the body itself, not the frost on top.

What would kill this stage

If Triton is ordinary outer-system ice and rock, captured as it is, Stage 6 comes off the table.