What If the Next Asteroid Doesn't Miss? Experts Model 22nd-Century Impact Scenarios

Scientists are war-gaming humanity's worst nightmare: an asteroid with Earth's name on it.

In April 2024, nearly 100 planetary defence experts gathered at Johns Hopkins Applied Physics Laboratory to confront a chilling hypothetical—a near-Earth object with a 72% chance of catastrophic asteroid impact in just 14 years.

The fifth biennial Planetary Defence Interagency Tabletop Exercise revealed an alarming reality. Even with decades of warning, planet Earth remains vulnerable to cosmic threats that could obliterate entire cities or trigger global catastrophe.

With over 20,000 known near-Earth objects (NEOs) and hundreds more discovered monthly by asteroid detection systems, the question isn't whether another significant impact will occur, but when.

'These hypothetical scenarios are complex and take significant effort to design,' explained Paul Chodas, director of NASA's Centre for Near Earth Object Studies (CNEOS). 'Our purpose is to make them useful and challenging for exercise participants and decision-makers to hone their processes.'

Europe's Bug-Eyed Space Telescope Takes Watch

ESA's revolutionary Flyeye telescope, currently completing tests in Italy, promises to transform asteroid tracking capabilities. Named for its insect-inspired design that splits light into 16 separate cameras, the space telescope can scan an area 200 times larger than the full Moon in a single exposure.

The first unit is expected to be operational atop Sicily's Monte Mufara by late 2025, with a second southern hemisphere telescope planned for 2028. This network aims to detect potentially hazardous asteroids larger than 40 metres several weeks before potential impact—enough time for evacuation, though not always for deflection.

'We are working to ensure Europe can detect hazardous asteroids a few weeks before a potential impact,' stated Holger Krag, Head of ESA's Space Safety Programme. The urgency is justified: scientists estimate thousands of city-killing asteroids remain undiscovered.

A Hypothetical Threat with Real Consequences

In April 2024, NASA's Planetary Defence Coordination Office (PDCO) led a tabletop exercise simulating a fictional asteroid with a 72% chance of impacting Earth in 14 years.

The asteroid, several hundred metres wide, was projected to strike heavily populated regions in North America, Southern Europe, or North Africa. After initial tracking, the object moved too close to the Sun, rendering it unobservable for seven months—a realistic complication that added urgency to the scenario.

Chodas explained: 'These hypothetical scenarios are complex and take significant effort to design, so our purpose is to make them useful and challenging for exercise participants and decision-makers to hone their processes and procedures to quickly come to a plan of action while addressing gaps in the planetary defence community's knowledge.'

The exercise underscored the urgency of preparing for a range of asteroid outcomes—not just global extinction events, but also regionally catastrophic strikes. As scientists refine models and response protocols, attention is increasingly turning to the specific effects of mid-sized impacts, whether on land or at sea.

Modelling the Consequences of Impact Events

• Local or Regional Devastation

A mid-sized asteroid (tens to a few hundreds of metres) striking land could devastate cities or regions. Simulations of thousands of impact events reveal the effects of blast, thermal radiation, and ejecta, including damaging shockwaves and firestorms.

• Ocean Impacts and Tsunamis

Many long-term models examine oceanic strikes, which could generate tsunamis. The magnitude depends on angle, depth, and location, but a coastal city might face flooding and severe damage. The Asteroid Impact Modelling Working Group regularly uses terrestrial analogues and simulations to improve scenario planning.

• Atmospheric Effects and Climate Disruption

Large impacts have the potential to inject dust and aerosols into the stratosphere, reducing sunlight and causing short-term 'impact winter' effects. For a massive object, this could lead to global crop failure and ecosystem stress.

In one recent hypothetical scenario, researchers projecting the effects of a Bennu impact in 2182 estimate that such a strike could inject 100–400 million tonnes of dust into the atmosphere, leading to global cooling, reduced precipitation, and disruption of photosynthesis for years.

ESA's Role in Global Preparedness

ESA has also played a key role in modelling asteroid impact scenarios. During the 2019 Planetary Defence Conference, ESA experts collaborated with NASA and civil protection agencies to simulate a week-long crisis response to a fictional asteroid threat.

Participants, including astronomers, government officials, and emergency planners, received daily updates and were tasked with making decisions under uncertainty, mimicking the real-world pressure of an evolving impact risk.

ESA's Flyeye telescope, currently under development in Italy, is designed to improve Europe's ability to detect and track NEOs. With over 20,000 known asteroids near Earth and hundreds more discovered monthly, early detection remains the cornerstone of any effective mitigation strategy.

Could We Stop It? Defence Strategies from Kinetics to Nukes

The most promising mitigation strategies include kinetic impactors, gravity tractors, and nuclear deflection, all of which require years of preparation and precise targeting. In a 22nd-century context, experts speculate that autonomous spacecraft powered by AI could be deployed to intercept hazardous asteroids long before they pose a threat.

However, success depends on early detection. If an asteroid is discovered too late or if its trajectory becomes unobservable due to solar interference, options narrow dramatically. In such cases, evacuation and disaster preparedness may be the only viable response.

• Kinetic Impactor

This method was successfully tested in NASA's DART mission, which struck the asteroid Dimorphos and altered its orbit, demonstrating that a spacecraft impact can deflect a smaller body.

• Nuclear Disruption/Detonation

For larger or later-detected hazards, a nuclear blast (on or near the asteroid) could fragment or redirect it. One concept spacecraft, HAMMER, is a NASA proposal for an 8-tonne craft capable of delivering a nuclear device to deflect or disrupt an incoming object.

• Laser Ablation/Mass Ejection

A more gradual approach involves heating part of the asteroid, causing material to vaporise and produce thrust. While speculative at scale, laboratory experiments show the principle is viable.

• Keyhole Avoidance and Gravity Assists

In long-term modelling, avoiding passages through 'gravitational keyholes' is critical. These are narrow regions in space where an asteroid's trajectory can be nudged into a future collision path with Earth.

Planetary defence working groups regularly convene to update and refine simulation tools. As recently as May 2024, the USGS Astrogeology centre hosted meetings to advance modelling techniques, disaster mitigation simulations, and mission planning.

Can Planetary Defence Systems Fight Back?

Our planetary defence arsenal remains limited, but it is growing. NASA's DART mission successfully altered an asteroid's orbit in 2022, demonstrating that kinetic impact technology is effective for mitigating smaller threats detected early enough.

For larger or later discoveries, nuclear deflection becomes necessary. NASA's proposed HAMMER spacecraft could deliver nuclear devices to fragment or redirect incoming objects. However, success requires years of warning—a luxury we might not have.

'A large asteroid impact is potentially the only natural disaster humanity has the technology to predict years in advance and take action to prevent,' noted Lindley Johnson, planetary defence officer emeritus at NASA Headquarters.

The 22nd Century NEO Threat Challenge

Future impact scenarios pose unique challenges. Experts modelling 22nd-century threats must account for technological evolution, potential political fragmentation, and climate instability affecting global coordination. ESA's Near-Earth Object Coordination Centre (NEOCC) and NASA's Sentry System continuously scan for potential impacts over the next century.

International collaboration proved essential during the recent exercise. 'This was a very successful tabletop exercise, with nearly 100 participants from US government agencies and, for the first time, international planetary defence experts,' said Terik Daly, who coordinated the exercise.

The ATLAS telescope network, with sites in Hawaii, Chile, and South Africa, provides crucial early warning capabilities. Meanwhile, ESA's upcoming NEO Surveyor mission, set to launch in 2027, will significantly enhance detection capabilities.

Yet simulations reveal troubling gaps. Misinformation, political inertia, and public panic could derail response efforts. Even with a decade's warning, governments may struggle to coordinate across borders when millions of lives are at stake.

As Earth's astronomical sentinels multiply and asteroid detection improves through tools like NASA's Eyes on Asteroids, humanity faces an uncomfortable truth: we're still remarkably unprepared for the asteroid that won't miss. The clock is ticking on building truly effective planetary defence systems—because, unlike Hollywood films suggest, last-minute heroics won't save us when cosmic reality strikes.