Initially enthusiastic about the prospect of humans living on Mars, the authors said their research turned them into space settlement skeptics. In "A City on Mars," authors Kelly and Zach Weinersmith argue substantially more research is needed before humans can safely populate Mars. Particular BooksCNN: Can humans settle Mars in the near term? KW: Musk is saying that in the next 30 years, we’re going to have a million people on Mars. It’s about 40% gravity and we know that humans in microgravity have all sorts of major problems, and what happens at 40% we just don’t know.

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Persons: Elon, Kelly, Zach Weinersmith, ”, Kelly Weinersmith, it’s, we’ll, you’ve, You’re Organizations: CNN, Society Trivedi, Rice University, NASA, JPL, Caltech, facie, Earth, United Nations Locations: “, Houston, Mars, United States, China