NASA cannot stop this asteroid: the 2026 Oxford study and what it found

01What the Oxford asteroid study found

The 2026 Oxford study modeled the effectiveness of current asteroid deflection technologies against a range of impactor sizes and warning times. Its central finding was that for asteroids above approximately 1 kilometer in diameter detected with less than 10 years of warning, no existing or near-term technology can reliably prevent an impact. The energy required to move such a mass exceeds what any current system can deliver.

The study also found that the critical variable is not just asteroid size but warning time. A small asteroid with days of warning cannot be deflected by any method, while a large one with decades of warning might be nudged off course through repeated small interventions. The intersection of large size and short warning time defines the worst-case scenario that current planetary defense cannot address.

02Which asteroid NASA cannot currently deflect

The study did not name a specific asteroid as an undeflectable threat, but it identified the class of objects that exceed current capability. These are asteroids in the 500-meter to 2-kilometer range, large enough to cause regional or global devastation, detected with insufficient lead time. The challenge is not that we lack the physics to deflect them but that we lack the launch infrastructure, response speed, and sustained thrust capacity to deliver enough energy.

NASA's DART mission in 2022 successfully demonstrated kinetic impact deflection on the asteroid Dimorphos, changing its orbit by a measurable amount. However, Dimorphos is roughly 160 meters across and was a test target, not a threat. Scaling that success to a kilometer-scale object on an impact trajectory would require either a much larger impactor, multiple missions, or a fundamentally different approach.

03Why current technology is insufficient

Current deflection technology falls short in three areas. First, launch capacity: moving a massive deflection payload requires heavy-lift rockets, and assembling or launching multiple payloads in sequence takes months or years. Second, response time: the process of designing, building, and launching a deflection mission currently requires years, and compressing that timeline below 5 years has not been demonstrated.

Third, energy delivery: a kinetic impactor transfers momentum through collision, but the deflection produced scales with the mass and velocity of the impactor. For a kilometer-scale asteroid, the mass required to produce a sufficient deflection may exceed what can realistically be launched. Nuclear standoff methods can deliver more energy but involve political and treaty constraints that make them a last resort rather than a first option.

04The probability and timeline of impact

The probability of a kilometer-scale asteroid impact in any given century is low, estimated at roughly 1 in 50,000 for a 1-kilometer object. However, the consequences are catastrophic enough that even a low probability warrants preparation. The study emphasizes that the risk is not from a known specific asteroid but from the population of undiscovered objects, particularly those in difficult-to-detect orbits.

The timeline concern is detection lag. Surveys have catalogued an estimated 95 percent of large near-Earth asteroids, but the remaining 5 percent, along with smaller but still dangerous objects, continue to be discovered. An object discovered with only a few years of warning would leave insufficient time for any current deflection method, and this is the scenario the Oxford study identifies as the most dangerous gap.

05What deflection methods were evaluated

The study evaluated five primary methods. Kinetic impactors, demonstrated by DART, are effective for smaller objects but scale poorly to kilometer-scale targets. Nuclear standoff detonation delivers the most energy but involves international treaty restrictions and the risk of fragmenting the asteroid rather than deflecting it. Gravity tractors, which use a spacecraft's gravitational pull to slowly shift an asteroid, are precise but extremely slow, requiring decades of station-keeping.

Laser ablation and ion beam shepherds are experimental concepts that could provide sustained thrust over long periods but are not flight-ready. Each method has a regime where it works and a regime where it fails, and the study's contribution is mapping those regimes systematically. No single method addresses the full range of threat scenarios, which means a layered defense combining multiple approaches is necessary.

06What the study recommends

The Oxford study's primary recommendation is investment in early detection. The most effective planetary defense strategy is to find threatening objects decades before any potential impact, because deflection becomes exponentially more feasible with longer warning times. The proposed NEO Surveyor space telescope, designed to detect asteroids in infrared from orbit, is identified as a critical capability.

The study also recommends developing rapid-response mission architectures that can be launched within months rather than years, and investing in multiple deflection methods so that the right tool is available for the specific threat. International coordination is emphasized, since asteroid defense is inherently a global challenge that no single nation should or can address alone.

07How the planetary defense community is responding

The planetary defense community has responded to the study with a mix of urgency and measured assessment. NASA's Planetary Defense Coordination Office has acknowledged the findings and emphasized that the identified gaps are known limitations, not new discoveries, but the systematic analysis provided by the Oxford team strengthens the case for increased investment.

The European Space Agency's Hera mission, which is conducting detailed follow-up observations of the DART impact site, is part of the response. Hera will provide data on how effectively kinetic impact modifies an asteroid's structure and orbit, information that is essential for planning future deflection missions. The community broadly agrees that while the worst-case scenario is low-probability, the cost of being unprepared is high enough that the investment is justified.