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Why could breaking up a dangerous asteroid create additional risks?

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The Chicxulub asteroid — Earth impact hazard An artist's rendering of the impact of a near-Earth object 66 million years ago in what is today the Caribbean region. Many scientists think that the collision of a large asteroid or comet nucleus with Earth triggered the mass extinction of dinosaurs and many other species near the end of the Cretaceous Period.

Breaking up a dangerous asteroid can create additional risks because the process may fail to sufficiently alter the object's trajectory to miss Earth.1

If a large object is fragmented without being adequately deflected, it could be broken into numerous smaller pieces that remain on a collision course with the planet. While these individual fragments would be smaller than the original body, they could still be potentially destructive upon impact. Because the physical properties of many near-Earth objects—such as their internal strength, density, and composition—are poorly understood, scientists caution that aggressive mitigation measures like using thermonuclear devices could inadvertently do more harm than good. Consequently, validating such strategies requires further theoretical research and controlled experiments to ensure that any intervention effectively mitigates the Earth impact hazard rather than exacerbating it.1