NASA estimates 4,700 potentially hazardous asteroids larger than 100 meters that could pose a danger to Earth. 70% of these haven’t even been discovered. Although improbable, what if we discovered a two-mile-wide asteroid with 1 in 1000 odds of hitting us? Should we worry? Would we do anything about it? How much warning would we need?

That’s the premise of a book written by former NASA spacecraft navigator Tony Taylor, who spent over 30 years navigating spacecraft through the solar system as a member of the Voyager, MESSENGER, Cassini, Mars Polar Lander, and Galileo missions, among others.