Planets and asteroids, in general, follow pathways that confine each one to its own zone of the Solar System. The unaided eye can see just a few such travelers across the sky—Sun and Moon and five major planets other than our own, Mercury, Venus, Mars, Jupiter, and Saturn, known to observers for millennia. A few objects don’t seem to follow quite the same rules, appearing temporarily, perhaps reappearing with predictable periodicity. But, like the planets, they are obedient to the call of gravity. These are the comets, in general with elliptical orbits that bring them swinging around the Sun, during a visit to our inner Solar System, and then take them out into deep darkness. And during that swing-by, they grow wispy tails, like trails of long fine hair that spread away from the Sun. Modern missions by our robotic spacecraft have taken away some of their old mystery but have deepened their own stories and ours, with discoveries of seeds of life in their dust.