SPACE: Sentinel’s Mission to Find 500,000 Near-Earth Asteroids: The privately funded space telescope will hunt for objects on a collision course with Earth. “Sentinel is the first space telescope dedicated to asteroid hunting. During six and a half years of operation, it will be able to spot more than 500,000 objects orbiting in the vicinity of Earth, dozens of times more than have been found to date. Not only could this rapid rate of detection reveal serious threats to the planet, it could also give people enough advance notice to do something about it. . . . Based on the geologic record and what we know about the NEO population, the probability of a catastrophic event is quite low. A Tunguska-scale event might occur once every few centuries. Impactors as large as the 10-km-diameter object that finished off the dinosaurs very rarely collide with Earth, just once every 100 million years or so. But of course, these are just average rates. The next asteroid with the potential to level a city might not hit Earth for hundreds of years; it could also arrive tomorrow. The only thing we can say with certainty is that there will be more collisions in our future. Given enough advance warning, though, we should be able to protect ourselves.”