Sort of. Etymologically, you're correct that 火曜日 originates as the term 火曜-日, the day (日) of the fire light (火曜).

But I don't think even most Japanese people are aware of this today; the only common use of 曜 is its use in the name of every weekday, so people think of 火曜日 as being segmented 火-曜日, the weekday ("曜日", etymologically spurious) of fire (火).

I don't know the modern Japanese word for Mars, but in Chinese it's 火星, not 火曜.