By Sam Blanchard For Mailonline
Published: 11:59 BST, 20 September 2019 | Updated: 12:55 BST, 20 September 2019
An asteroid which had a 'close pass' with Earth in July had not been picked up by NASA until the agency was told about it just hours before it swept past.
Internal emails have revealed the US space agency was caught by surprise by the asteroid named '2019 OK'.
It passed about 40,400 miles away from Earth, still a harmless distance, but was the largest rock to have done so in almost 100 years.
Emails obtained through Freedom of Information revealed one NASA staffer telling colleagues the asteroid had 'slipped through the net'.
Travelling at 55,000mph and measuring 426 feet by 187ft (57m x 130m), NASA only realised 2019 OK was coming 24 hours before it passed.
The 2019 OK asteroid was only noticed 24 hours before passing Earth at a distance of about 40,000 miles, travelling at 55,000 miles per hour (stock image)
Buzzfeed News revealed internal emails from the space agency which saw staff there giving one another the heads up that they might be asked about it.
One, from NASA's planetary defense officer, Lindley Johnson, said: 'Because there may be media coverage tomorrow, I'm alerting you that in about 30 mins a 57-130 meter sized asteroid will pass Earth at only 0.19 lunar distances (~48,000 miles).
'2019 OK was spotted about 24 hrs ago.'
Asteroid 2019 OK passed relatively close to Earth, at about 70,000 kilometers away (43, 496 miles). For an object of its size, many said that was too close for comfort
An observatory in Brazil was the first to spot 2019 OK and alert the team in the US.
After the asteroid had passed a news release warned that it could have destroyed an area measuring 50 miles across, something which only happens about once every 3,000 years.
NASA's Paul Chodas wrote in an email two days after 2019 OK had passed: 'This object slipped through a whole series of our capture nets.
'I wonder how many times this situation has happened without the asteroid being discovered at