NASA said it wants to send humans to Mars by 2030, and in 2016, it selected six private U.S. companies, including Boeing, Lockheed Martin, and Bigelow Aerospace, to develop prototypes for deep space habitats.

At the beginning of the year, Tesla CEO and SpaceX founder Elon Musk discussed sending 1 million people to colonize Mars by the year 2050 by scheduling three Starship launches a day.

That may sound like science fiction, but SpaceX has taken preliminary steps toward making it a reality—this year, the company will ramp up testing of its manned spacecraft by bringing astronauts to the ISS. However, astrophysicists have been quick to point out that human travel to Mars would have some difficult hurdles to overcome, not the least of which is radiation.

As Columbia University astronomer Caleb Schart said, explaining of the perils of space travel, “in the worst case scenario (which may or may not be a realistic extrapolation) there’s a chance you’d end up dead or stupid on Mars. Or both.”