Planetary defence
Finding, tracking and, if needed, deflecting asteroids and comets that might hit Earth.
Big impacts are rare, but they do happen, and unlike most natural disasters they can be predicted and even prevented. Planetary defence has three parts. First, survey telescopes search the sky for near-Earth objects and calculate their orbits. Second, experts work out the risk of any future collision and plan how to warn people. Third, space agencies test ways to change an asteroid's path, ideally years before any impact.
The most famous test was NASA's DART mission. On 26 September 2022 it deliberately crashed into Dimorphos, a small moon of the asteroid Didymos. The impact shortened Dimorphos's orbit by about 32 minutes, far more than the minimum goal, showing that a 'kinetic impactor' can nudge an asteroid. The European Space Agency's Hera spacecraft, launched in October 2024, is designed to study the aftermath in detail.
Real events show why this matters. On 15 February 2013 an asteroid about 18–20 metres across exploded over Chelyabinsk, Russia. It was not spotted in advance, and the shock wave broke windows across the city, injuring around 1,500 people, mostly from flying glass. Many fragments were recovered as an LL chondrite meteorite.
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Level: Explorer Ages 10 and up