Problem is it has no atmosphere. How are they going to get around that?
It has an atmosphere. That’s why our helicopter can fly. It’s mostly carbon dioxide. Pretty sure Earth had a lot more carbon dioxide before green plants.
Problem is it has no atmosphere. How are they going to get around that?
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It’s a very thin atmosphere, but sufficient for flight.
Mars does have an atmosphere that is one percent as dense as Earth's. As you go further down into any planet the atmospheric pressure increases just as it does when you go from a mountain down to sea level on Earth. I have no idea what that maximum atmospheric density could be but you can say with certainty that it would be denser than the open air.
Also, when one moves to deeper regions, the upper layers exert pressure and thus permit the existence of liquid water in principle. For instance, Mars does not currently have any longstanding bodies of water on its surface, but it is known to have subsurface lakes at the poles.
I myself would be surprised if there is no bacterial type life inside the surface of Mars. I wouldn't be surprised if there is a genetic relationship either.