When researchers found an unusual linkage between solar flares and the inner life of radioactive elements on Earth, it touched off a scientific detective investigation that could end up protecting the lives of space-walking astronauts and maybe rewriting some of the assumptions of physics. It’s a mystery that presented itself unexpectedly: The radioactive decay of some elements sitting quietly in laboratories on Earth seemed to be influenced by activities inside the sun, 93 million miles away. Is this possible? Researchers from Stanford and Purdue University believe it is. But their explanation of how it happens opens the door to yet another mystery. There is even an outside chance that this unexpected effect is brought about by a previously unknown particle emitted by the sun. “That would be truly remarkable,” said Peter Sturrock, Stanford professor emeritus of applied physics and an expert on the inner workings of the sun.