They said it couldn’t be done. They said the atmosphere on Mars is too thin to support a helicopter.
But the Smithsonian magazine has a story about the prototype NASA has tested (it works!). It’s planned to be onboard a rover mission launching in 2020. So for all Sci Fi writers dealing with the human future on Mars, you can now include a surveillance helicopter in your story and refute any nay-sayers. Stay tuned for further details.