The world’s first major private geoengineering start-up must have known it’d have skeptics. The basic premise—dimming the sun to artificially cool the planet—has been called reckless by scientists and climate advocates; military analysts have said it has real security risks. (Don’t even get conspiracy theorists started.) Still, Stardust Solutions, an American-Israeli company planning to build a solar-reflecting system in the next few years, has enough fans that it raised $60 million in 2025.