Non-Periodic Comets
This might be a good reason to build a lunar base. We should use an electromagnetic rail gun on the moon to launch nuclear flash-bangs that help whole-sky-survey telescopes spot Kuiper Belt objects up to 60 light-hours distance from the Sun. Even if one is coming right toward us, at that distance we'll have 50 years advance warning. We'll know where to look to get better tracking too.