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Fortunately, NASA and other agencies closely track asteroids passing through Earth's cosmic neighborhood, discover hundreds more each year, and haven't found any that might potentially threaten our planet in the next 100 years or so.
On Jan. 26, a small asteroid ("about the size of a box truck," NASA said) passed just 2,200 miles from Earth. Because it's so small, the rock, dubbed "2023 BU," was only found by an amateur astronomer on Jan. 21, when it journeyed nearby. It was never a threat. Even if it hit Earth, it would "largely disintegrate harmlessly in the atmosphere," NASA explained.
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Here's what you need to know about Asteroid 2023 BU (which passed over the southern tip of South America) and other near-Earth asteroids:
1. NASA did not issue a warning about Asteroid 2023 BU
NASA's Jet Propulsion Laboratory, which runs the agency's Center for Near Earth Object Studies, keeps track of the asteroids that pass relatively closeto Earth, though many of these rocks pass millions of miles away, because space is vast. Technically, a near-Earth object (NEO) is one that passes within some 30 million miles of our planet's orbit around the sun.
2023 BU, then, easily qualifies as a near-Earth object. But because it wasn't ever a threat — it had no chance of hitting Earth and was too small to be a danger — NASA and other U.S. agencies didn't issue a warning about it. You may have read sensational headlines claiming "NASA warns asteroid will pass close to Earth," but that's simply wrong. A warning would be a serious escalation, implying a threat.
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"We have never actually issued a warning," NASA’s Planetary Defense Officer, Lindley Johnson, told Mashable in 2021. If it turns out a rock larger than 30 feet wide has greater than a one percent chance of hitting Earth, NASA will give an official warning to the White House and other government leaders, who will then assess the situation and inform the public about any potential strike.
In this case, NASA released some brief information on 2023 BE and how it was detected. Indeed, it's an interesting little event. "In fact, this is one of the closest approaches by a known near-Earth object ever recorded," NASA engineer Davide Farnocchia said in a statement.
2. Asteroids aren't often a threat to Earth
Generally, the bigger the asteroid, the larger the threat it poses to Earth.
The rock that likely wiped out the dinosaurs is in the biggest class of asteroids, meaning over 0.6 miles wide. The dino rock was a roughly six-mile-wide behemoth. But these are exceedingly rare visitors. As Mashable reported last year:
No known asteroidover 460 feet across will threaten Earth in the next century or so (a rock some 460 feet across is an asteroid big enough to cause substantial devastation).
Impacts by objects around 460 feet in diameter occur every 10,000 to 20,000 years.
"Dinosaur-killing" impacts from rocks perhaps a half-mile across or larger happen on 100-million-year timescales.
Importantly, asteroids smaller than 460 feet can still be a huge threat. Even an asteroid some 100 to 170 feet across could destroy a place like Kansas City, home to half a million people. So the surveys for rocks large and "small" are vital.
A NASA graphic showing known asteroids (blue dots) in our solar system. Credit: NASA 3. Astronomers watch for potentially dangerous asteroids
Large, specialized telescopes are devoted to finding new near-Earth asteroids. Taxpayer money is involved in this: NASA has a congressionally-directed mandate to find 90 percent of all space rocks 460 feet wide or larger.
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Pan-STARRS: The Panoramic Survey Telescope and Rapid Response System atop Maui is comprised of two telescopes peering up at the sky and looking for unusual movement. With its keen eyesight, Pan-STARRS found 253 of the 456 near-Earth asteroids larger than 460 feet wide discovered in 2021, and has been a leader in these detections for the past decade.
Catalina Sky Survey:This survey's three telescopes are located in Arizona's Santa Catalina Mountains. While Pan-STARRS tends to find more NEOs larger than 460 feet wide (or 140 meters), Catalina tends to find a bit more NEOs overall. That's good, because something under 140 meters is still quite capable of devastation.
ATLAS: The Asteroid Terrestrial-impact Last Alert System acts like a huge floodlight looking closely around Earth. It's comprised of three telescopes: one in Hawaii, one in Chile, and one in South Africa that can scan the entire sky each night. They can spot something around 65 feet across a few days out.
So far, astronomers have found about 40 percent of the rocks 460 feet across or bigger, with hundreds more being found each year. Meanwhile, they've identified an estimated 95 percent of the largest "planet-killer" asteroids.
A chart showing how many near-Earth asteroids have been discovered, so far. Credit: NASA Importantly, some smaller asteroids will inevitably slip through the survey cracks. That's why other astronomical sleuths are so valuable. The amateur astronomer Gennadiy Borisov found 2023 BU, informed other astronomers, and it was reported to an international organization that tracks such objects, called the Minor Planet Center. A few days later, NASA's Center for Near Earth Object Studies confirmed the asteroid and its trajectory.
So when you hear about an asteroid "heading towards Earth," remember that it's likely not a threat (asteroids regularly come within millions of miles of Earth), experts are vigilantly watching the skies, and if something big should actually threaten Earth, space agencies like NASA will be around to provide coherent information about where it's going (likely the expansive ocean) and what you need to do (usually nothing).
Enjoy the skies. Yes, have a healthy respect for the big space rocks orbiting the sun. But if you see a warning on the internet about an incoming asteroid, carry a strong dose of skepticism.
This story has been updated with addition information about Asteroid 2023 BU.