⊕ is the symbol for earth. R⊕ is earth-radius, as you guessed. It is domain-specific, so it should probably be changed in the title. I will say that it is a v

⊕ is the symbol for earth. R⊕ is earth-radius, as you guessed. It is domain-specific, so it should probably be changed in the title. I will say that it is a very nice symbol - easy to write out by hand, makes for quick note-taking. Same for the symbol used for the sun (which isn't rendering for me, but is a circle with a dot in the middle). https://en.wikipedia.org/wiki/Planet_symbols https://en.wikipedia.org/wiki/Planet_symbols