Sulfur is one of the most abundant elements in the universe. If you peer into a diffuse interstellar cloud, you find loads of it—about the amount expected based on fusion patterns in the stars it was born in. However, if you look at a dense, cold molecular cloud—the kind where those stars actual ly form—it seems like 99% of the sulfur expected to be there is missing. Scientists have puzzled over this "missing sulfur problem" for decades, though a leading theory is that the element hides in icy dust grains, making it hard to detect. ...read more read less