Why is the trip to Mars a one-way trip?

M: Hello, Jennifer.
W: Hello, Callum.
M: Do you like to travel?
W: Oh, yes. I love going to new and interesting places.
M: What do you think of the idea of a one-way trip to Mars?
W: You do mean the planet Mars?
M: Well, this is what is being planned at the moment by a company in the Netherlands. They are planning to send people to Mars and the people who go would never be able to come back to Earth.
W: Sounds like quite a trip!
M: What is interesting about it is that this would be a one-way trip.
W: Why is this a one-way trip?
M:(1)It’s about technology. Although we do have the knowledge and technology to get people to Mars, we can’t get them back.
W: That’s a big commitment, isn’t it? But I imagine some people will jump at the opportunity. But what kind of person are they going to recruit for this "trip of a lifetime" ?
M: They want smart people, which means clever, intelligent people. These people need to be healthy both physically and mentally. They also need people with very specific skills.
W: I would think so.
M:(2-1)And there is something more important.
W: What’s that?
M:(2-2)Character. You need to have die right personality.
W: What other characteristics are they looking for?
M:(2-3)They want people who can still work well when things are bad, people who are calm in a crisis.(3-1)So from what you’ve heard, does it sound like a job for you?
W:(3-2)Absolutely not. I don’t mind travelling but I think it’s a bit far for me. And what about you?
M:(3-3)No, it’s not for me, I have to say. I’m not made of the right stuff.