Four years ago, the SpaceX founder and CEO went on "The Late Show With Stephen Colbert" and discussed a strategy for making the Red Planet more livable: detonating nuclear bombs over its poles .

This terraforming concept is apparently still bouncing around in Musk's head, because on Thursday (Aug. 15), he tweeted, seemingly unprompted, "Nuke Mars!"

For starters, many scientists and exploration advocates have concerns about any terraforming effort: Do we have the right to fundamentally transform another world — especially one that might host its own uniquely adapted life even today — for our own purposes?

A 2018 study published in the prestigious journal Nature Astronomy concluded that Mars doesn't harbor enough CO2 today to achieve significant warming even if all the stuff were liberated into the atmosphere.

Namely, it could backfire, ushering in a "phenomenon known as 'nuclear winter' (akin to the asteroid impact that killed off the dinosaurs), wherein you generate so much dust and particles that they literally block out a significant portion of the incoming sunlight, cooling down the planet," climate scientist Michael Mann of Penn State University told U.S. News and World Report via email in 2015.

He wants to help humanity colonize the Red Planet , and he's building a spaceflight system to help make it happen — a 100-passenger spaceship called Starship and a huge rocket known as Super Heavy.