Even much about the surface of Mars is a mystery.

Lawrence thought it looked more like the surface of Mars.

Their hope is that humans will eventually be able to walk on the surface of Mars without a suit.

The city's name has been given to a crater on the surface of Mars.

There is no liquid water on the surface of Mars.

The pressure at that altitude is about the same as on the surface of Mars.

And water that has been on the surface of Mars before, yes?

Don't think about running around the surface of Mars without your space suit just yet though.

Dark sand dunes are common on the surface of Mars.

My responsibility is to the men and women here on the surface of Mars.