... Astronomers have found roughly 95 per cent of the near-Earth objects larger than 1km, and none of them poses any threat to Earth. We know much less about the smaller ones. An asteroid as slender as 50m across can wreck a city. Of the nearly quarter of a million that are around that size in Earth’s neighbourhood, 93 per cent remain undiscovered. ...
In July 1994, fragments of a comet called Shoemaker-Levy 9 smashed into Jupiter, and Nasa, for the first time ever, caught the spectacle on video. Later that summer, Congress tasked Nasa with mapping all near-Earth objects larger than 1km, sobered by the sight of the comet’s cataclysmic Earth-sized impacts. The brief was then expanded to include 90 per cent of all objects 140m or larger — a task that is still less than halfway complete. ...
In 2028, Nasa plans to launch an infrared asteroid-detecting telescope called NEO Surveyor. The following year, which the UN has designated “International Year of Asteroid Awareness and Planetary Defence”, an asteroid called Apophis [~375m] will pass within 32,000km of Earth, closer than some satellites. A Nasa spacecraft is on its way to study Apophis in detail. ...
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