As long as we are a single-planet species, we are vulnerable to extinction by a planetwide catastrophe, natural or self-induced. Once we become a mul….

Before we go there and set up greenhouses, dance clubs, and falafel stands, let's make sure that, in some subtle form that could be harmed by the hum….

The planet Mars -- crimson and bright, filling our telescopes with vague intimations of almost-familiar landforms -- has long formed a celestial tabu….