  We discuss a hypothetical existential threat from a 10 km diameter bolide
discovered 6 months prior to impact with one case being a comet and the other
being an asteroid. We show that an extension of our work on bolide
fragmentation using an array of penetrators but modified with small nuclear
explosive devices (NED) in the penetrators, combined with soon-to-be-realized
heavy lift launch assets with positive $C_3$ such as NASA SLS or SpaceX
Starship (with in-orbit refueling) is sufficient to mitigate this existential
threat. A threat of this magnitude hitting the Earth at a closing speed of 40
km/s for the comet and 20 km/s for the asteroid would have an impact energy of
roughly 65 Teratons TNT, or about ten thousand times larger than the current
combined nuclear arsenal of the entire world. This is similar in energy to the
KT extinction event that killed the dinosaurs some 66 million years ago. Such
an event, if not mitigated, would be an existential threat to humanity. We show
that mitigation is conceivable using existing technology, even with the short
time scale of 6 months warning, but that the efficient coupling of the NED
energy is critical.
