Earth dodged an asteroid by just 6 hours, crossing paths with a potential city-killer

In 1989, Earth crossed paths with an asteroid that missed us by only a few hours. It is one of the closest and most terrifying "near misses" in modern astronomical history. NASA has an Asteroid Watch program managed by the Jet Propulsion Laboratory, the Center for Near Earth Object Studies (CNEOS), to monitor potential space rocks that could threaten Earth. Multiple asteroids cross near our planet daily; however, none pose a danger. The asteroid watch program officially began in 1998, and so nine years earlier, when a space rock came into Earth's orbit, scientists only got to learn about it after nine days had passed.

Asteroid 4581 Asclepius was estimated to be about 1,000 feet in diameter. “An impact would have released a devastating amount of energy equivalent to about a gigaton of TNT, which is 67,000 times the energy output of the Hiroshima atomic bomb,” Harvard professor Avi Loeb told WION. A massive shock wave would have levelled cities, experts said.

So what exactly happened in 1989?

The asteroid flew past Earth on March 22, 1989, at a comfortable distance of 684,000 km, nearly twice the distance between our planet and the Moon. But this was not a hazardous event, even though in cosmic terms, this is still quite near. The orbits of Earth and asteroid 4581 Asclepius led them to travel through a common point in space, but at different times. The asteroid was at the same point in our orbit where Earth was just six hours ago.

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Basically, the asteroid crossed a point in Earth's orbit, and our planet was in that spot just six hours earlier. Just a little bad timing would have been enough to send the asteroid flinging into our planet. The surprising thing is that nobody knew that the asteroid was there. Astronomers Henry Holt and Norman Thomas only discovered the close call at the Palomar Observatory on March 31, 1989. Humanity dodged a bullet, literally.

Effect of asteroid impact on Earth

Asteroid 4581 Asclepius was 1,000 feet in diameter, about the size of three football fields. It was travelling at a speed of 74,000 km/hr, which means an impact would have been catastrophic. It would have released energy equivalent to roughly 600 megatons of TNT. For comparison, the Tsar Bomba, or the RDS-220, the most powerful nuclear weapon ever made by man, yielded energy equivalent to 50 megatons of TNT. The asteroid would have gouged a crater nearly 10 kilometres wide, vapourised the immediate impact zone and generated a massive shock wave. If it had slammed into the ocean, tsunami waves hundreds of feet high would have been generated, wiping out coastlines.

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How does Asclepius compare to the dinosaur-killing asteroid?

The asteroid that struck the Yucatán Peninsula in Mexico, creating the massive Chicxulub crater, was roughly 10 kilometres in diameter, or nearly 50,000 feet. In comparison, Asclepius was only 1,000 feet, and so was a city-killer asteroid, while the Chicxulub Impactor was a "Planet-Rebooter."

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How Asclepius changed asteroid watch

Asclepius miss served as a wake-up call, as before the Asteroid Watch program, only a handful of people observed near-Earth objects as an academic interest. Asclepius's movement past Earth led to a push for automated, computerised sky surveys and dedicated planetary defence initiatives. Today, we not only have a mission dedicated to looking out for the asteroids, but we also have plans to deflect potentially dangerous space rocks. The DART mission was one such test that slammed into the moonlet of an asteroid.