Would we be prepared if a potentially life-threatening object from space were on a collision course with Earth? And how much damage could an incoming asteroid actually cause?
Such questions remain at the forefront of increasingly sophisticated planetary defense efforts aimed at protecting our planet from potentially hazardous asteroids. Yet even if astronomers are able to identify a space object that might pose a threat, a significant number of uncertainties remain: the object’s size, composition, structure, and potential impact locations all must be considered, as these factors can dramatically influence what happens once an asteroid enters Earth’s atmosphere.
Fortunately, planetary defense scientists are working to address these challenges, developing new technologies and assessment methods that could help mitigate the consequences of a future impact event.
The Asteroid Threat
Depending on their composition and structure, asteroids may disintegrate high above Earth’s surface, producing powerful atmospheric explosions known as airbursts. In other cases, some objects survive their passage through the atmosphere and strike the ground, as evidenced by the numerous ancient impact craters found across our planet.
The resulting hazards can vary considerably, ranging from destructive shock waves and intense heat to impact craters, flying debris, and potentially tsunamis. Scientists are developing increasingly powerful tools to investigate these possibilities, although one major challenge remains the limited amount of direct observational data available from actual impact events.
“One of the fundamental challenges in evaluating the potential damage from an asteroid impact—and in planetary defense more broadly—is that there are many large uncertainties and very little direct data across all aspects of the problem,” says Lorien Wheeler, the Impact Risk Assessment lead for NASA’s Asteroid Threat Assessment Project (ATAP) at the NASA Advanced Supercomputing Division at Ames Research Center.
Wheeler recently told The Debrief that uncertainties like an asteroid’s size, potential impact zone, and also the space rock’s composition all influence whether a direct strike or an atmospheric airburst is more likely to occur, as well as how much energy is released and what kinds of damage may result.
Adding further complexity are the limitations based on what methods of observation are used by astronomers, as well.
“The amount of information we might be able to get about an asteroid before it reaches Earth would depend a lot on what telescopes or missions are able to observe it,” Wheeler told The Debrief.
Assessing Asteroid Risk
Wheeler and her team’s work at NASA Ames involves the agency’s Probabilistic Asteroid Impact Risk (PAIR) model, which is used to assess the range and likelihood of damage from potential asteroid impacts on Earth. This research supports the broader efforts of NASA’s Planetary Defense Coordination Office.
As Wheeler explained to The Debrief, even asteroids that break apart before reaching Earth’s surface can pose serious risks.
“Asteroids are extremely varied in their structures and properties, ranging from weak, loosely bound rubble piles to strong, dense, iron-type monoliths,” Wheeler explained. “When you combine those structural and density uncertainties with the size uncertainties, you get a huge range in the potential mass and energy that could airburst or impact Earth.”
Preparing for the Next Tunguska?
Given the uncertainties planetary scientists face, advanced computer simulations have become essential tools for assessing asteroid impact risks. These simulations help researchers like Wheeler and her colleagues model the complex physics of atmospheric entry, fragmentation, and impact damage.
Using probabilistic risk models that evaluate millions of hypothetical impact scenarios, scientists can estimate the range and relative likelihood of different outcomes. This approach allows decision-makers to prepare for the most probable scenarios while also accounting for less likely but potentially catastrophic possibilities.
Additionally, NASA’s Center for Near-Earth Object Studies (CNEOS) regularly participates in planetary defense exercises designed to test these assessment methods, with current scenarios under development for the 2027 Planetary Defense Conference that take a cue from one of history’s most concerning airburst events.
“The current exercise that is underway for the 2027 Planetary Defense Conference is based around a hypothetical impact threat from a roughly Tunguska-sized object,” Wheeler told The Debrief.
Even with data that has been collected on the Tunguska airburst, presently, there are still too many variables to fully account for all the potential problems such an event might cause if something similar were to occur today.
“Even if we knew the size and mass ahead of time, it is difficult to predict how much or how quickly a particular asteroid body could break up during entry, how high or low it might airburst or impact, and how much energy would then go into producing different types of damage such as blast waves, heat, cratering and ejecta, or tsunami waves,” Wheeler told The Debrief.
Given the many variables involved, scientists cannot predict every possible consequence of an asteroid impact with certainty. However, the increasingly sophisticated simulations and risk-assessment models researchers like Wheeler employ in their work are significantly improving their ability to evaluate potential threats and inform planetary defense strategies.
“All of these uncertainties are very important to take into account when evaluating potential asteroid threats and developing planetary defense plans, such as mitigation missions or emergency response planning,” Wheeler said.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.