Sentry (monitoring system)

Sentry is a highly automated collision monitoring system that continually scans the most current asteroid catalog for possibilities of future impact with Earth over the next 100+ years. Whenever a potential impact is detected it will be analyzed and the results immediately published on the Near Earth Object Program. Two or three weeks of optical data is not enough to conclusively identify an impact years in the future. By contrast, eliminating an entry on the risk page is a negative prediction; a prediction of where it will not be. From the point of view of the general public, it isn't worth getting worried about an object with a couple of weeks of optical data showing a possible Earth encounter years from now.