THE FUSE

For about a century, astronomers looking at Venus in ultraviolet light have seen dark streaks and patches sweeping across a planet that appears blandly pale yellow to the eye. Nobody has identified what makes those markings. An international team has now done something more useful than guessing: it has calculated how strongly the material inside Venus's cloud droplets must absorb light, and the number is demanding enough that many long-proposed candidates struggle to meet it.