The first earthling in space was a dog.
What about Mars or Venus.
I am looking for a word for an inhabitant of Mars (and another word for the inhabitant of Venus) that "feels" the same as earthling.
Martian seems to me more like the equivalent of human/man than an general living organism living on the planet Mars. For example, most people don't imagine a bacteria from Mars when you say "Martian". They imagine homanoid-like creature from the planet Mars. That is why I see the word martian as an equivalent of human or man and not an equivalent of earthling.