It looks inconsequential enough, the faint little spot moving leisurely across the sky. The mountain-top telescope that just detected it is taking it very seriously, though. It is an asteroid, one never seen before. Rapid-survey telescopes discover thousands of asteroids every year, but there's something very particular about this one. The telescope's software decides to wake several human astronomers with a text message they hoped they would never receive. The asteroid is on a collision course with Earth. It is the size of a skyscraper and it's big enough to raze a city to the ground. Oh, and it will be here in three days.
Meanwhile, the Russians have it so under control, they laugh at our fears. I.O. Yarkovsky discovered if you hit the rock with a giant blob of white paint, it will send it spinning off target. The white disrupts the absorption of sunlight on the black surface. (Absorption and reflection of solar energy push it through space, we hope.)