The brightest kilonova ever was detected and challenges current gamma-ray burst models. Plus, the history of water on both Venus and Mars, how radioactive elements may help habitability, and a little-known mass extinction event here on Earth. But wait! There’s more… new images of the Perseus Cluster, a recaptured 1960s rocket booster, the shortest measurement of time, a treasure trove of copies of Principia, and SpaceX is certified to launch Crew-1 this weekend.