• Scientists announced the asteroid discovery just hours before its close approach
• Asteroid 2019 OK is about 100 meters wide, and came within 70,000 km of Earth
• At its closest approach on Thursday night, it was closer to Earth than the moon
• Experts say impact from object of this size would be enough to 'devastate a city'  

A close shave this week with an asteroid estimated to be about 100 meters wide is yet another unnerving reminder of how ill-prepared we are for the threat of rogue space rocks.

Scientists with the Brazilian SONEAR survey detected the object, dubbed 2019 OK, on Wednesday and it was soon after confirmed by Ohio State’s All-Sky Automated Survey for Supernovae network.

By the time it was announced, 2019 OK was just hours away from its closest approach – which put it at a distance closer to Earth than the moon.

Thankfully, experts found it poses no immediate threat, and the asteroid zipped by without incident.

But, the surprise appearance has left many feeling unsettled.

A close shave this week with an asteroid estimated to be about 100 meters wide is yet another unnerving reminder of how ill-prepared we are for the threat of rogue space rocks. Artist's impression

‘The lack of warning shows how quickly potentially dangerous asteroids can sneak up on us,’ Monash University astronomer Michael Brown wrote in an essay for The Conversation.

Asteroid 2019 OK passed relatively close to Earth, at about 70,000 kilometers away (43, 496 miles).

For an object of its size, many say that’s a bit too close for comfort.

While it isn’t large enough to bring on an Armageddon-style event reminiscent of the dinosaur-killing asteroid, Brown notes that a moderate-size impact ‘could devastate a city.’

By the time of its closest approach, asteroid 2019 OK would have been bright enough in the sky to be seen with just a pair of binoculars, the astronomer says.

‘Such bright fly-by isn't often -- once per a few years if my memory serves,’ Caltech astronomer YE Quanzhi noted on Twitter.

Since its discovery, scientists have traced the path of asteroid 2019 OK and even retrospectively spotted it in observations gathered back in June.

According to the experts, it will be a few years before it comes around again.

‘2019 OK has a very elliptical orbit, taking it from the asteroid belt beyond Mars to within the orbits of both Earth and Venus,’ Brown says.

‘As each orbit takes 2.7 years, it isn’t always going to pass as close to Earth as it did this time. It will make close approaches in the future, but hopefully not quite this close.’

These smaller objects are what currently remain among the biggest concerns in planetary defense.

Asteroid 2019 OK passed relatively close to Earth, at about 70,000 kilometers away (43, 496 miles). For an object of its size, many say that’s a bit too close for comfort

NASA estimates it has already found over 90 percent of near-Earth objects measuring one kilometer or larger – which would have catastrophic global effects in the event of a collision.

But, smaller space rocks are much harder to detect.

The space agency has been working to pinpoint NEOs in the 140-meter range, with a goal of identifying at least 90 percent of these objects.

Asteroid 2019 OK, however, reminds us that they can still pop up without warning.

And, though the risk of this and other known objects of its size crashing into Earth may be small, Brown notes, ‘they would be devastating if they did.’

HOW IS NASA STEPPING UP ITS EFFORTS TO STOP DEADLY ASTEROIDS HITTING EARTH?

The US government is stepping up efforts to protect the planet from incoming asteroids that could wipe out entire regions or even continents.

The National Science and Technology Council released a 20-page report on June 21 calling for improved asteroid detection, tracking and deflection.

The initiative backed by Nasa, federal emergency officials, and the White House aims to coordinate efforts over the next 10 years to detect and respond to possible threats in Earth's vicinity, should they arise.

Near-Earth objects (NEOs) include all asteroids and comets that orbit within 30 million miles of Earth, Nasa said.

The U.S. government is stepping up efforts to protect the planet from incoming asteroids that could wipe out entire regions or even continents

While the probability of an asteroid impact may be low, the effects could be cataclysmic.

For now, scientists know of no asteroids or comets heading our way. But one could sneak up on us - and that's why the government wants a better plan.

Nasa's planetary defense officer, Lindley Johnson, says scientists have found 95 percent of all near-Earth objects measuring one kilometer (two-thirds of a mile) or bigger.

But the hunt is still on for the remaining five per cent and smaller rocks that could still inflict big damage.

The new document, titled 'The National Near-Earth Object Preparedness Strategy and Action Plan,' established five strategic goals to reduce the risk of an asteroid strike.

These included better methods for detecting and tracking the objects, improved modelling, the development of technologies to deflect NEOs, increased international cooperation on the subject, and the establishment of emergency procedures.