In 1992, astronomers calculated that the comet behind the Perseids could slam into Earth in 2126 — until 2,000-year-old Chinese star charts called off the doomsday.
Comet Swift-Tuttle — the icy nucleus responsible for every Perseid meteor streaking overhead each August — was discovered independently by Lewis Swift and Horace Tuttle in July 1862. Its debris trail is what Earth plows through every summer, producing the shower's signature fireballs.
In 1973, astronomer Brian Marsden calculated the comet's orbit and predicted it wouldn't return until 1992, correctly guessing the 1862 comet was the same object seen in 1737. When Swift-Tuttle reappeared right on schedule in September 1992, it was hailed as one of the great orbital predictions in astronomy.
But there was a catch: the comet's actual arrival was off from Marsden's prediction by 17 days. If that same drift repeated on its next pass, he calculated, Swift-Tuttle could strike Earth on August 14, 2126 — a possibility he felt obligated to publish.
The warning made headlines as the 'doomsday comet' — the unsettling idea that the same comet behind a beloved summer meteor shower could one day end civilization.
Amateur astronomer Gary Kronk set out to shrink the uncertainty by hunting for older sightings of the comet. He found it had likely been recorded by Chinese astronomers in 69 BCE and again in 188 CE — observations that predated telescopes by nearly two thousand years.
With those ancient records folded into the comet's orbital history, Marsden recalculated the trajectory and formally called off the warning: Swift-Tuttle would pass a comfortable 15 million miles from Earth in 2126, not through it.