Solar System How much water covered Mars’ surface, and which areas had the most water? Why did it disappear?
Science What would our solar system look like if aliens observed it with the same telescope used to image three planets around the star HR 8799?
Science In stellar magnitude estimates, why do larger numbers represent dimmer objects? Shouldn’t it be the other way around?
Cosmology, Exotic Objects Could large numbers of black holes account for much of the “dark matter” estimated to exist in our universe?
