ΔE 16.7, loose: different enough that you should pick on purpose. Burnt Sienna is much more saturated, cooler than Martian Ironearth. They are different kinds of paint: Citadel Martian Ironearth is a technical paint or medium and Golden Burnt Sienna is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Burnt Sienna is much more saturated, cooler than Martian Ironearth. They are different kinds of paint.
The same difference applies the other way round: Martian Ironearth is much more muted, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Martian Ironearth on the colour wheel See Burnt Sienna on the colour wheel
All matches: Martian Ironearth equivalents · Burnt Sienna equivalents