Scientists find a massive, 23-mile-wide meteorite crater hiding deep beneath the ice in Greenland. The new crater is just 100 miles from a 19-mile-wide crater discovered just 3 months ago, which was tentatively linked to the mysterious, 1,000-year period known as Younger Dryas.

That's not entirely true about detecting it years in advance. If the object is reflective enough to be seen, then yeah, they can be seen easily if you're looking in the right spot. But most stuff in space is not very reflective, and extremely small compared to planets. A 10 mile wide chunk of iron would be devastating to life on earth. Think about how hard it is to find something 10 miles wide when it's 1 billion miles away from you...and not very reflective. Most of the time, we don't see these things until they're around Saturn or Jupiter. That only gives us a few months to figure something out. Then it has to work perfectly the first time. Realistically, if something big is gonna hit earth, we can't stop it.

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