1) Our bodies and metabolisms are highly attenuated to not just the physical environmental thingamabobs of Earth, but also the specific relative chemical abundances (at least surface abundances). Another planet may be able to support water and an oxygen atmosphere (assuming O2 won’t waft away into space like it would in the weak gravity and “warming” sunlight of Mars or the Moon), but plants and animals would get all puny-like without Earthlike abundances of trace chemicals.
This is a good point to be exploited.
We have first the environment of outer space with a different gravity which causes in us several health problems as faster osteoporosis, low levels of red cells, deformed discs in our backs, distortion of our bodies, and more. Without the proper care our bodies probably should end as spread mass in the floor like jello.
So, I can predict right now that astronauts will have to use drugs in order to help them to survive better in long trips in outer space…there is no other choice by now.
After this “adaptation” in the space ship, the astronauts will have to “adapt again” in the planet where they will land. The problem is that the health problems will be unknown until they arrive over there.
So, they will have to have several drugs of all kind to help them to survive over there, otherwise they will have to live in the space ship for weeks, months and even years until they find the right ones.
What about if unknown bacteria or viruses attack them and no medicine is available?
You have lots of possible negative events which may cause the fast extinction of the astronauts right with their landing in such new home in another planet.
It appears that today people have been watching to many movies about astronauts traveling and finding a new home in other planets “with a similar atmosphera like ours”, but here we are not discussing about fiction movies with such happy endings.
We must be realistic and take in consideration the pros and cons of this idea of traveling to another planets to inhabit them.
Of course, Hawking still living in the days of Einstein when Einstein thought that traveling to outer space was like to traveling from New York to Washington DC in a train. Both are still ignorants that space traveling causes lots of health damages to astronauts…and it appears that some posters here also suffer of such deliberate ignorance.