"What is Mars". "What is on Mars" but not "What is there on Mars"
Native English speaker here and I'd definitely say it's "What is there on Mars?"
What is Mars? = Mirihi ni nini?
What is on Mars? = Nini kiko Mirihi?
What is there on Mars? = Kuna nini Mirihi? / Mirihi kuna nini?
Sorry the answer it produced was "What is there AT Mars" - my mistake in feedback (to eager). Your answer is correct I am a native speaker too.