  We investigate a variety of short warning time, terminal mitigation scenarios
via fragmentation for a hypothetical impact of asteroid 2023 NT1, a Near-Earth
Object (NEO) that was discovered on July 15, 2023, two days after its closest
approach to Earth on July 13. The asteroid passed by Earth within ~0.25 lunar
distances with a closest approach distance of ~10$^{5}$ km and speed of 11.27
km/s. Its size remains largely uncertain, with an estimated diameter range of
26 - 58 m and probable diameter estimate (weighted by the NEO size frequency
distribution) of 34 m (JPL Sentry, September 12, 2023). The asteroid approached
Earth from the direction of the Sun, as did both the Chelyabinsk asteroid in
2013 and comet NEOWISE in 2021. As a result, 2023 NT1 remained undetected until
after its closest approach. If it had been on a collision course, it would have
had an impact energy of ~1.5 Mt (assuming a spherical asteroid with the
probable diameter estimate of 34 m, 2.6 g/cm$^{3}$ uniform density, and impact
speed of 15.59 km/s). 2023 NT1 represents a threat that could have caused
significant local damage (~3x Chelyabinsk airburst energy). We utilize the PI
("Pulverize It") method for planetary defense to model potential mitigation
scenarios of an object like 2023 NT1 through simulations of hypervelocity
asteroid disruption and atmospheric ground effects for the case of a terminal
defense mode. Simulations suggest that PI is an effective multimodal approach
for planetary defense that can operate in extremely short interdiction modes
(with intercepts as short as hours prior to impact), in addition to long
interdiction time scales with months to years of warning. Our simulations
support the proposition that threats like 2023 NT1 can be effectively mitigated
with intercepts of one day (or less) prior to impact, yielding minimal to no
ground damage, using modest resources and existing technologies.
