Many,
Atmospheric pressure doesn't exist, so we would have to be able to control our internal pressure, Not enough oxygen so make your lungs adapt to run on less oxygen, no water,
and
gravity related problems
First we would have to actually make a successful trip to Mars...
No oxygen, no water and no food would make for a quick demise of a man on Mars.
mars has liquid water on it
mars has liquid water on it
it is possible to live on Mars but to do this you would need an atmosphere, and to have an atmosphere you need gases. To make these gases (there have been discussions about this) you would need to build factories to give off green house gases and make an atmosphere, because Mars is extremely cold at night, then we would have to get people to Mars. This would cost billions and would take a long time to build the atmosphere.
the skier moved her helmet aside
It would make absolutely no difference.
ad trees in its cage
For a verb to be transitive it must have a subject and an object. In order to make "moved" a transitive verb, the sentence would have to begin with a subject who did the moving and end with an object that was moved by the subject.
Probably the Babylonians were the first to observe and record the presence of Mars, which would make it around 700 BC.
in 3 days
Life on Mars would have to have the ability to deal with a harsher environment. They would have to be able to handle an atmosphere that has more carbon dioxide than Earth as well as much colder temperatures.