The largest asteroid to pass as close to the Earth in a century “slipped through” Nasa’s detection systems, internal emails reveal.

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?”

Race to Space: US and Soviet Union's Cold War rivalry Show all 8 1 /8 Race to Space: US and Soviet Union's Cold War rivalry Race to Space: US and Soviet Union's Cold War rivalry US astronaut Alan B Shepard Jr sitting in his Freedom 7 Mercury capsule, ready for launch on 5 May 1961. Just 23 days earlier, Soviet cosmonaut Yuri Gagarin had become the first man in space. After several delays and more than four hours in the capsule, Shepard was ready to go, and he famously urged mission controllers to “fix your little problem and light this candle”. Pictures by Nasa/EPA Race to Space: US and Soviet Union's Cold War rivalry Wernher von Braun (centre) explains the Saturn rocket system to President John F Kennedy at Launch Complex 37 while the president tours the Cape Canaveral Missile Test Annex, on 16 November 1963 Nasa/EPA Race to Space: US and Soviet Union's Cold War rivalry A back-up copy of the first Russian Sputnik (satellite, right), and a small replica of the second Russian satellite displayed in a small museum in the cosmonaut training centre in Star City outside Moscow. The second satellite was launched just a month later on 3 November 1957 with dog Laika on board. EPA Race to Space: US and Soviet Union's Cold War rivalry Jet propulsion laboratory director William Pickering (left), Dr James Van Allen (centre), and Dr Wernher von Braun (right) hold up a model of the first US satellite Explorer 1, which successfully launched on 31 January 1958 Nasa/EPA Race to Space: US and Soviet Union's Cold War rivalry President Kennedy speaks to the nation at the joint session of congress, in Washington, DC, on 25 May 1961, where he said: “I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to Earth.” Nasa/EPA Race to Space: US and Soviet Union's Cold War rivalry A visitor passes in front of a picture of Yuri Gagarin, the first cosmonaut of the USSR, inside the Vostok 1 command capsule on display at the exhibition “The way of Gagarin – achievement of Russian manned cosmonautics” in Moscow. On 12 April 1961, Gagarin performed a space flight aboard the Vostok-1 spacecraft, orbiting Earth in 108 minutes and landing safely near Smelovka village in the Saratov region's Ternovsky district. EPA Race to Space: US and Soviet Union's Cold War rivalry A model of the world’s first artificial satellite, Sputnik 1, hangs in the Smithsonian National Air and Space Museum in Washington, DC EPA Race to Space: US and Soviet Union's Cold War rivalry Full length image of US astronaut Alan B Shepard Jr Nasa/EPA

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.

Will a giant asteroid really hit earth in 2019?

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.