ΔE 16.9, loose: different enough that you should pick on purpose. Grunge Brown is a little darker, much more muted, cooler than Mars Orange.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Grunge Brown is a little darker, much more muted, cooler than Mars Orange.
The same difference applies the other way round: Mars Orange is a little lighter, much more saturated, 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 Mars Orange on the colour wheel See Grunge Brown on the colour wheel
All matches: Mars Orange equivalents · Grunge Brown equivalents