Elon Musk has revealed what he believes would make a planned city on Mars successful.
Musk, the founder of SpaceX, has previously spoken about his desire to send humans to Mars and build a settlement on the red planet by 2050.
At this year's Mars Society convention last week, Musk set out what he believes would make such a city successful.
"The acid test, really, is, if the ships from Earth stop coming from any reason, does Mars die out?" he said.
According to The Independent, Musk believes the settlement would need to be self-sustainable in case of a cataclysmic event on Earth, noting that "civilisation's not looking super strong" at the moment.
"This really might come down to: Are we going to create a self-sustaining city on Mars before or after World War 3? And I think the probability of it being created after World War 3 – hopefully there’s never a World War 3 – but the probability of after is low, so we should try and make the city self-sustaining before any possible World War 3."
Last year, the billionaire revealed what he called the "holy grail of space", a rocket prototype he hoped one day would allow crew and cargo to travel to the Moon and Mars. He wants to see humans become a "multi-planet species".
"We need to make space travel like air travel," he said. "Any other mode of transport is reusable so the critical breakthrough is a rapidly reusable orbital rocket."
Musk had a goal of producing 1000 of the so-called Starships over 10 years. It was then intended that an average of three Starships would be launched per day to allow anyone to travel to Mars. Each Starship would carry 100 people.
"Needs to be such that anyone can go if they want, with loans available for those who don’t have money," Musk tweeted in January.