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sentry (plural sentries) 1  A guard, particularly on duty at the entrance to a military base. ( 2 uncountable) Sentry duty; time spent being a sentry. ( 3 nautical) A form of drag to be towed underwater, which on striking bottom is upset and rises to the surface.
The following table summarizes by object the potential future Earth impact events that the JPL Sentry System has detected based on currently available observations. Click on the object designation to go to a page with full details on that object. 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.