More pocked with craters than any other object in our solar system, Jupiter's outermost and second-biggest Galilean moon, Callisto, appears geologically unremarkable. In the 1990s, however, NASA's ...

What’s your purpose in life? It’s a daunting question. But your answer may say a lot about your well-being. Studies link a sense of purpose to better physical and mental health. But your purpose isn’t ...