Asteroid 2023 NT1 passed within about a quarter of the Moon’s distance of Earth on July 13, 2023, and astronomers did not see it until two days after the flyby. That near miss has become the basis for a modeling study testing what planetary defense could actually do with that little warning. The simulations, published in The Astrophysical Journal (2025) and updated on arXiv in July 2026, suggest a threat like 2023 NT1 could be broken apart with an intercept one day or less before impact, reducing the expected ground damage to minimal or none.
The study is the work of a team led by Brin Bailey, Alexander N. Cohen and Philip Lubin of the University of California, Santa Barbara, with colleagues at Sandia, Los Alamos and NASA Ames. It applies a planetary defense concept called Pulverize It (PI), a NASA Innovative Advanced Concepts (NIAC) Phase II study, to the specific case of 2023 NT1. The asteroid itself poses no danger: on September 16, 2023, JPL’s Sentry system removed it from its impact risk page after additional observations ruled out a future collision. The paper models a hypothetical version of events in which the asteroid hit Earth on July 13 instead of narrowly missing.
If it had hit, the consequences would have depended on its size, which remains uncertain. Observations constrain its diameter to a range of 26 to 58 m, with a most probable estimate of 34 m based on the NEO size frequency distribution. Assuming a spherical body of 34 m with a uniform density of 2.6 g/cm3 and an impact velocity of 15.59 km/s, the authors estimate a collision would have released about 1.5 Mt of energy, roughly three times the Chelyabinsk airburst of 2013. That event, caused by an 18 m asteroid, injured more than 1,600 people and damaged over 7,000 buildings.
The short warning time is the point. Most planetary defense work targets asteroids found years or decades ahead of a potential impact, which allows time for a deflection mission such as NASA’s DART. But smaller asteroids, the most common threats, are poorly tracked: as of September 2024 the authors cite estimates that about 94% of near-Earth asteroids larger than 1 km have been discovered, compared with roughly 44% of those larger than 140 m. Objects below that size, a population estimated at nearly three billion, are mostly unknown. 2023 NT1 demonstrated the gap: it was discovered with the ATLAS-Sutherland telescope in South Africa on July 15, 2023, two days after its closest approach at about 10:13 TDB, meaning it had already passed Earth by the time astronomers noticed it.
Pulverize It takes a different route from deflection. Instead of nudging the asteroid onto a new orbit, the concept relies on intentional robust disruption: an array of hypervelocity kinetic penetrators slams into the body and shatters it into many small fragments, typically under 10 m. With long warning, the fragment cloud misses Earth entirely. In the “terminal mode” studied here, the intercept happens hours to days before impact and the fragments enter the atmosphere as a dispersed series of airbursts, spreading the asteroid’s energy over time and space instead of concentrating it in one event.
The team simulated the interception with the ALE3D hydrodynamics code from Lawrence Livermore National Laboratory, modeling the asteroid as a rubble pile: spherical boulders 0.5 to 8 m across embedded in a weak binder, with strengths chosen conservatively, from about 1 Pa in the binder to 250-500 MPa for the hardest boulders, approximating steel and titanium. The penetrator is a tungsten cylinder with a 10:1 length-to-diameter ratio, and the scenarios assume a closing velocity of about 20 km/s, which the authors say is within reach of current launch vehicles such as the Falcon 9.
For a 20 m asteroid, a single penetrator with an idealized mass of 100 kg (137.4 kg realized in the simulation) delivered a specific impact energy of about 1,309 J/kg, more than 13 times the 100 J/kg limit conventionally associated with catastrophic disruption. The mean fragment was about 1 m across with a velocity of 9.3 m/s, about a thousand times the asteroid’s escape velocity, so the pieces would not recombine. The largest fragment was 4.3 m. For a 50 m analogue, both a single 500 kg penetrator and an array of five 100 kg penetrators achieved disruption, with the single penetrator transferring more than twice as much kinetic energy to the fragments.
The key question for a terminal intercept is what reaches the ground. The authors set two damage thresholds: 200 kJ/m2 of optical energy, the point at which leaves and paper can ignite, and 3 kPa of acoustic overpressure, associated with residential window breakage. They then ran more than 100 threat scenarios varying the asteroid’s diameter, density, entry angle, fragment number and intercept time, measuring each against these thresholds using the 1% value of the cumulative distribution: the level exceeded at only 1% of ground locations.
For the probable 34 m case, a one-day intercept with 1,000 fragments keeps the 1% values at 3.5 kJ/m2 of optical energy and 0.5 kPa of overpressure, roughly 60 and 6 times below the respective thresholds. An intercept 12 hours before impact still yields acceptable levels, about 9.0 kJ/m2 and 0.8 kPa. Even for the upper-end 58 m estimate, a one-day intercept with 1,000 fragments stays below threshold at 28.7 kJ/m2 and 1.2 kPa. Dense metallic analogues at 6 g/cm3 come closer to the limits: a 58 m case broken into 4,000 fragments one day before impact yields 105 kJ/m2 and 2.6 kPa, dropping to 35.0 kJ/m2 and 1.6 kPa with a two-day intercept. The unmitigated comparison is stark: an unfragmented 34 m asteroid would produce 1% values of 357 kJ/m2 and 5.0 kPa, and a 58 m one about 6,500 kJ/m2 and 21 kPa, both exceeding the thresholds.
The paper also contrasts the launch mass required. Deflecting a 26 m asteroid with one day of warning would need roughly 200 metric tons of deflector spacecraft under conservative assumptions, or about 3,000 metric tons for the 58 m case; fragmentation of the same threats could be accomplished with a single 100 kg penetrator. The authors caution that the method is untested: the interior structure of rubble-pile asteroids is poorly known and is modeled speculatively, and the approach has not been exercised outside simulations. They argue for a layered defense combining deflection for long warning times and fragmentation for short ones, and note the unresolved question of whether an impact expected over uninhabited land should be mitigated at all.
Sources
1. Bailey, B., Cohen, A. N., Egan, S., Lubin, P., Xu, R., Boslough, M., Robertson, D. K., Silber, E. A., Sagert, I., Korobkin, O., Sjoden, G. “Evaluating Short-Warning Mitigation via Intentional Robust Disruption of a Hypothetical Impact of Asteroid 2023 NT1.” arXiv:2310.13112 (v5, 2026-07-30); The Astrophysical Journal (2025), vol. 981, pp. 181-197, DOI 10.3847/1538-4357/adb289. https://arxiv.org/abs/2310.13112
2. arXiv listing for 2310.13112: submission history, journal reference, license. https://arxiv.org/abs/2310.13112