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One year ago today, the Arecibo radio telescope in Puerto Rico took a close look at a passing asteroid. And it reported some good news: the asteroid isn’t a threat to hit Earth anytime soon.
Asteroid 2020 NK1 had been discovered just weeks before. Early observations indicated it had a small chance of hitting Earth in 2043.
Astronomers have discovered about 25,000 asteroids that routinely pass close to Earth. Some of them come close enough that they’re considered a hazard — they could someday slam into Earth. About 160 of those are at least a kilometer in diameter — big enough to cause destruction across hundreds of thousands of square miles.
Arecibo astronomers had planned to take a look at NK1 on July 30th. But a tropical storm was passing over the island, so they had to wait until the next day. They beamed radio waves at the asteroid, which was five million miles away. Reflected radio waves were captured by the thousand-foot telescope. They revealed that NK1 is about a kilometer long — making it especially deadly if it hit. But Arecibo tracked the asteroid long enough, and with enough accuracy, to nail down its orbit. That showed that NK1 will miss us by a couple of million miles.
Arecibo tracked many other asteroids over the years. But cables that supported the telescope’s receivers broke last fall, forcing a shutdown. And the whole thing collapsed in December — demolishing an astronomical watchdog.