There are no known Earth-crossing minor planets large enough that a shelter on the other side of the world would be destroyed. All of them are approximately the size of the dinosaur-killer asteroid or smaller. We’ve surveyed of the large ones and there are no foreseeable impact risks from them.
Large asteroids are easier to detect from a long distance. A very large asteroid would have to come in from some previously unknown, unexpected orbit for it to be previously undetected. So probably a comet-like orbit, which for a large asteroid is probably ridiculously unusual.
I really don’t know how big it would have to be to destroy a solid underground or underwater structure. Maybe around the size of the Vredefort asteroid if not larger. But we haven’t had such an impact since the end of the late heavy bombardment period, three billion years ago, when these objects were cleared from Earth’s orbit.
The big threat is from comets, because we have not tracked the vast majority of them. There is evidence in periodicity of bombardment that would correlate with the perturbation of the Oort Cloud of comets (see the book Global Catastrophic Risks). Burned-out comets can be very dark, and we would have little warning.
There are no known Earth-crossing minor planets large enough that a shelter on the other side of the world would be destroyed. All of them are approximately the size of the dinosaur-killer asteroid or smaller. We’ve surveyed of the large ones and there are no foreseeable impact risks from them.
Large asteroids are easier to detect from a long distance. A very large asteroid would have to come in from some previously unknown, unexpected orbit for it to be previously undetected. So probably a comet-like orbit, which for a large asteroid is probably ridiculously unusual.
I really don’t know how big it would have to be to destroy a solid underground or underwater structure. Maybe around the size of the Vredefort asteroid if not larger. But we haven’t had such an impact since the end of the late heavy bombardment period, three billion years ago, when these objects were cleared from Earth’s orbit.
The big threat is from comets, because we have not tracked the vast majority of them. There is evidence in periodicity of bombardment that would correlate with the perturbation of the Oort Cloud of comets (see the book Global Catastrophic Risks). Burned-out comets can be very dark, and we would have little warning.