Darrel Robertson

How does the energy deposition profile (light curve), deceleration, and penetration depth in Earth's atmosphere depend on asteroid composition and meteorite type? Here, we present the light curve and velocity profile of 75 bolides from camera‐documented meteorite falls. The light curves as a function of altitude generally develop in the following seven phases: Phase (1) an initial rapid brightening; (2) a gradual increase that sometimes shows periodic brightness variations; (3) an onset and rapid increase of brightness until reaching a plateau; (4) a plateau with occasionally chirping brightness oscillations; (5) flares that result in fragments in the meteor wake; (6) an end flare of sometimes different color; and (7) ongoing ablation and fragmentation until dark flight. These seven phases are interpreted as resulting from solid bodies that cause early brightness oscillations from meteoroid spin, a plateau because of melting and reaching melting equilibrium, chirping oscillations due to plasma instabilities, flares due to fragmentations along fractures from dynamic pressure and thermal stress, and an end flare when the surviving back of the meteoroid explodes. This paper discusses the systematics of how the phase heights depend on entry speed, entry angle, initial mass, and meteorite type. The dynamic pressures during the onset of fragmentation and the end flare correlate with the tensile strength of the recovered meteorites. The results have implications for Planetary Defense when anticipating the energy deposition curve of small solid‐body airbursting asteroid impacts like Chelyabinsk .

The landscape of scientific publishing and communication is changing rapidly with the accelerating growth of open‐access outlets that lack rigorous peer review, revenue‐driven online media, inadequately trained journalists, social media, online influencers, podcasts, celebrity endorsements of pseudoscience, anti‐science political movements, and the emergence of artificial intelligence. Near‐Earth objects, impacts, and airbursts—particularly when related to global catastrophes or planetary defense—often attract intense public interest and the kind of media coverage that is prone to the spread of misinformation. The field of planetary defense has profound consequences, so maintaining public trust is essential to its success. Scientists cannot afford to ignore these challenges merely because they fall outside the scope of conventional scientific discourse. This paper classifies several types of misinformation, presents representative case studies in planetary defense and planetary science, and offers practical approaches for mitigation. We consider (1) rapidly evolving news events requiring timely expert response; (2) intermediate‐term cases involving inadequately reviewed publications, overpromotion, and uncritical reporting; and (3) long‐term, persistent, and self‐perpetuating myths that can grow organically and insidiously, even within the scientific community. We also discuss how misinformation can originate and proliferate through inadequate peer review, news releases and press conferences, exploitation of limited scientific literacy, unsubstantiated claims, and amplification of false narratives by artificial intelligence. Finally, we suggest proactive strategies for preventing and correcting misinformation, with particular attention to its implications for planetary defense.

We investigate various short-warning mitigation scenarios via fragmentation for a hypothetical impact of asteroid 2023 NT1, a near-Earth object (NEO) that was discovered on 2023 July 15, 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 of ∼1 × 10⁵ km and a velocity of 11.27 km s⁻¹. Its size remains largely uncertain, with an estimated diameter range of 26–58 m and a most probable estimate of 34 m (JPL Sentry, 2023 September 15; weighted by the NEO size frequency distribution). If 2023 NT1 had collided with Earth, it could have caused significant local damage. Assuming a spherical asteroid with a diameter of 34 m, uniform density of 2.6 g cm⁻³, and impact velocity of 15.59 km s⁻¹, a collision would have yielded an estimated impact energy of ∼1.5 Mt, approximately 3 times the energy of the Chelyabinsk airburst in 2013. We analyze the effectiveness of mitigation via intentional robust disruption for objects similar to 2023 NT1. We utilize Pulverize It (PI), a NASA Innovative Advanced Concepts study of planetary defense via fragmentation, to model potential mitigation scenarios through simulations of hypervelocity asteroid disruption and atmospheric ground effects in 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, in addition to long interdiction timescales with extended warning. Our simulations support the proposition that threats like 2023 NT1 can be effectively mitigated with intercepts of 1 day (or less) prior to impact, yielding minimal to no ground damage.

Modern civilization has no collective experience with possible wide-ranging effects from a medium-sized asteroid impactor. Currently, modeling efforts that predict initial effects from a meteor impact or airburst provide needed information for initial preparation and evacuation plans, but longer-term cascading hazards are not typically considered. However, more common natural disasters, such as volcanic eruptions, earthquakes, wildfires, dust storms, and hurricanes, are likely analogs that can provide the scope and scale of these potential effects. These events, especially the larger events with cascading effects, are key for understanding the scope and complexity of mitigation, relief, and recovery efforts for a medium-sized asteroid impact event. This paper reviews the initial and cascading effects of these natural hazards, describes the state of the art for modeling these hazards, and discusses the relevance of these hazards to expected long-term effects of an asteroid impact. Emergency managers, resource managers and planners, and research scientists involved in mitigation and recovery efforts would likely derive significant benefit from a framework linking multiple hazard models to provide a seamless sequence of related forecasts.

Asteroid 2008 TC₃ impacted the Earth's atmosphere with a known shape and orientation. Over 600 meteorites were recovered at recorded locations, including meteorites of nonureilite type. From where in the asteroid did these stones originate? Here, we reconstruct the meteor lightcurve and study the breakup dynamics of asteroid 2008 TC₃ in 3‐D hydrodynamic modeling. Two fragmentation regimes are found that explain the lightcurve and strewn field. As long as the asteroid created a wake vacuum, the fragments tended to move into that shadow, where they mixed with small relative velocities and surviving meteorites fell along a narrow strip on the ground. But when the surviving part of the backside and bottom of the asteroid finally collapsed at 33 km altitude, it created an end flare and dust cloud, while fragments were dispersed radially with much higher relative speed due to shock–shock interactions with a distorted shock front. Stones that originated in this final collapse tended to survive in a larger size and fell over a wider area at locations on the ground. Those locations to some extent still trace back to the fragment's original position in the asteroid. We classified the stones from this “large mass” area and used this information to glean some insight into the relative location of recovered ureilites and ordinary and enstatite chondrites in 2008 TC₃.