Venus could be the ultimate example of what can happen when an atmospheric greenhouse effect runs away. A mission to the planet four billion years ago might have shed some light on what is happening on Earth. But Esa's Venus Express probe will instead foc
Do we want clocks accurate to one second every 30 billion years? At that precision, gravity weighs down the passage of time - though it might be easier to find your way around the planet. Richard Corfield reports.