Named 2019 OK by scientists, the asteroid nearly passed by undetected as it came five times closer to Earth than the moon, documents obtained by Buzzfeed via freedom of information requests revealed.
It was first detected by a Brazilian observatory on 24 July just hours before coming within roughly 73,000km of Earth. Nasa’s failure to spot the 100-metre wide space rock highlighted longstanding concerns about a lack of US government funding for asteroid detection efforts.
“This object slipped through a whole series of our capture nets, for a bunch of different reasons,” Dr Paul Chodas, manager of Nasa’s Centre for Near Earth Object Studies, wrote to colleagues on 26 July.
“So, was this just a particularly sneaky asteroid? I wonder how many times this situation has happened without the asteroid being discovered at all?”
The emails showed space agency employees rushing to discover how the asteroid avoided detection, after a colleague alerted them to the near-miss “because there may be media coverage tomorrow”.
Nasa telescopes did spot the asteroid on 7 July, but it was moving too slowly to be identified as a near-Earth object. By the time it sped up it was too close to a nearly full moon for astronomers to detect, according to the emails.
A planetary defence officer at Nasa had written that 2019 OK appeared to be the largest asteroid to pass so close to earth in the last century. Another such event was not expected to occur until 2029, they said.
While there was never a chance the asteroid would have collided with Earth, a news release sent out weeks later by Nasa said: “If 2019 OK had entered and disrupted in Earth’s atmosphere over land, the blast wave could have created localised devastation to an area roughly 50 miles across.”
The failure to identify the space rock as a near-Earth object highlights the need to better fund detection efforts.
The US congress has tasked the space agency with detecting, tracking and cataloguing 90 per cent of objects larger than 140 metres in diameter pass close to the Earth by 2020.
While the Trump administration has placed great emphasis on returning to the moon, a June report released in June by the US National Academy of Sciences urged that better detection methods and infra-telescopes were needed for Nasa to meet its 2020 target.
“It is interesting to note that if a space-based infrared telescope had been on station and scanning the skies two years ago, it probably would have detected 2019 OK back then and this year’s close encounter would not have been a surprise,” Dr Chodas said in Nasa’s August press release.
At the Planetary Defence Conference in May, a virtual asteroid slammed into New York after Nasa scientists and international experts failed to stop it in a simulation designed to test the response to such a real-life scenario.
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