Bigger than a planet? Smaller than an atom? Size comparison videos are all the rage and may scratch a very old itch. By Jenny Marder Not long ago, my 7-year-old son looked up from a picture he was ...

During its 4.5-billion-year life span, Earth’s been hit by countless asteroids. (Despite Jupiter’s noble attempts at defending it.) But while it’s easy to imagine the damage they’ve done, just how big ...