Just a few days ago, Musk took to Twitter to re-propose his idea of nuking Mars to warm up the Red Planet and eventually terraform it. He has now doubled down on those claims, clarifying his “vision” and adding a new possibility.
Musk said in his tweet: “Might make sense to have thousands of solar reflector satellites [satellite emoji] to warm Mars vs artificial suns (tbd).”
The idea of using mirrors to converge solar radiation is certainly not new. We can go back all the way to Archimedes and the mirrors he allegedly used against the Romans, or stick to a more Mars-related study. In 2006, then-undergraduate Rigel Woida looked at heating up a small area of Mars using a mirror 1.5 kilometers (almost a mile) across composed of 150 segments that are each 150 meters (492 feet) across.
The mirrors would be made of mylar, a reflective material that is currently employed as a solar sail by the LightSail2 project. While the project had enough potential to get a $9,000 grant from NASA, it focused on warming a tiny area of Mars, roughly 1 square kilometer. (0.38 square miles). The surface of Mars is 144.8 million square kilometers (55.9 million square miles) – even a few thousand mirrors wouldn't cut it.
Musk also clarified his idea of nuking Mars in reply to the mirror tweet: “Nuke Mars refers to a continuous stream of very low fallout nuclear fusion explosions above the atmosphere to create artificial suns. Much like our sun, this would not cause Mars to become radioactive.”
This is different from the idea he touted a few years ago to liberate trapped CO2 from the Martian polar caps. Current hydrogen bombs (the nuclear fusion explosions he’s referring to) release nuclear fallout because their trigger is created either by uranium or plutonium. Sure, small explosive devices have a lower amount of fallout, but you would need a large number of these devices to constantly go off. And that’s just to mimic the amount of radiation Earth gets from the Sun.
The underlying issue that's not being discussed is that while Musk throws around outlandish solutions to warm up Mars, there is still not a single one that would keep it warm. As far as scientists can tell, there is simply not enough carbon dioxide on Mars to create a greenhouse effect and keep the planet warm. Without an atmosphere, whatever solution they choose will have to be permanent.
The mirrors will require constant refueling to continue to orbit Mars and not be pushed about by solar radiation. And if the nuclear explosion is more your style, you would have to constantly nuke the higher atmosphere of the Red Planet.
To reiterate what researchers in Nature Astronomy concluded last year, we currently do not have the technology to terraform another planet.