Late last month, a space rock about the size of a football field barreled past our planet by the smallest of margins – 45,360 miles (65,000km) – only one-fifth of the distance to the Moon. The asteroid, dubbed '2019 OK', has since been classified as a "city killer", theoretically capable of killing hundreds of thousands if it hit a populated area on Earth. While this is nothing new, the incident was all the more alarming because the rogue space rock caught scientists almost totally unaware.
Although astronomers spotted OK 2019 a few days before its uncomfortably close encounter with Earth, it seems no-one was aware of the asteroid's route, and of the narrow margins involved, until shortly before the asteroid event occurred.
This 'un-recognition' of an asteroid, despite being photographed, will be used to test the Flyeye
Professor Michael Brown, of Monash University's School of Physics and Astronomy, told Express.co.uk: "" It was startling to have an asteroid this large pass so close with so little warning.
"That said, we're getting better at discovering these asteroids before they get uncomfortably close. 2019 OK was independently discovered by two different teams of astronomers and 2019 OK was in images taken a few weeks before its close approach, but unfortunately not recognized.
"Our ability to find these asteroids will improve with new software, cameras and telescopes, including the Large Synoptic Survey Telescope
Asteroid close approach: 2019 OK last month hurtled past Earth at an “uncomfortably close” proximity
Asteroid close approach: 2019 OK flew fits the smallest of margins
"While not good to have these asteroids sneak up on us, this has to put context. Asteroids this size hits the Earth perhaps every 1,000 to 10,000 years and usually hit sparsely populated areas. Being a real risk, but as an astronomer I see climate change as a more significant threat and challenge than 100 meters asteroids. "
Royal Institution of Australia's Professor Alan Duffy described the flyby as "uncomfortably close".
The asteroid was initially spotted by both the Scientific Optical Network (ISON) and Southern Observatory for Near-Earth Asteroids Research (SONEAR), but this slow space rock appeared to move just a tiny amount between images, and was therefore not recognized.
Professor Krzysztof Stanek, of Ohio State Univerity also admits "It was quite a wake-up call. "
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He told Express.co.uk "It was seen by a Brazilian team roughly 24 hours before the closest approach.
"But because of the way these space rocks move, you can't determine its orbit if you see it just once.
"The big question is the sky is very big and we're not really observing it.
"We could but we didn't. And this thing just snuck up on us.
"We knew about it roughly a day before the flyby which wasn't long enough to do anything.
"It was seen by a Brazilian team roughly 24 hours before the closest approach.
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Asteroid close approach: A meteor exploded over Chelyabinsk in 2013
"But because of the way these space rocks move, you can't determine its orbit if you see it just once."
"This 'un-recognition' of an asteroid, despite being photographed," explains Rüdiger Jehn, ESA's Head of Planetary Defense, "will be used to test the software going into the European Space Agency's (ESA) upcoming asteroid-hunting telescope, the Flyeye ".
NASA's ESA and US space agency are tracking thousands of asteroids in the Solar System, leading several commentators to question why it was discovered so late.
However, there is currently no single obvious reason apart from 2019 OK's slow motion in the sky before close approach.
2019 OK also travels in a highly elliptical orbit, taking it from within the orbit of Venus to well beyond that of Mars.
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Asteroid 2019 okL This image shows the rogue space rock
This means the time it spends near Earth and is detectable with current telescope capabilities is relatively short.
A land impact cold obliterate an entire city while a plunge into the ocean could cause tsunamis that impact low-lying land.
In either scenario the asteroid would change the climate for many years.
NASA estimates it has already found over 90 percent of near-Earth objects measuring 1km or larger – which would have catastrophic global effects in the event of a collision.