We Dodged a Bullet

Earlier this week, an asteroid roughly the size of a football field came within 71,000 kilometres of the Earth. If it had hit, it would have had an impact equivalent to a hydrogen bomb. Such flybys are not uncommon, and asteroids of that size or close to it do hit the Earth, but what distinguished this one is that astronomers didn't detect it until just before the flyby.

A team at the SONEAR Observatory in Brazil first noticed the asteroid on Wednesday, and it appeared in another American team’s data later that day, before flying by hours later. The asteroid itself was between 53 and 130 meters in diameter (187 and 426 feet), or as several astronomers have referred to it, “a city killer.” It was not a city killer, of course—it didn’t hit a city, and probably would not have hit a city had it hit the Earth. Still, how do you miss something like that?

Well, these asteroids are incredibly faint, and a few hundred feet might sound large if it pummels the Earth, but that’s incredibly small on astronomical scales. Even if these rocks eventually get close enough that we can actually detect them, survey telescopes must be looking at the right place in the sky when the blips pass by.

The United States Congress has been pushing NASA to detect and track threatening asteroids. In 1998, the Congress told NASA to find the near-Earth asteroids larger than a kilometer in size within 10 years, and in 2005, expanded that goal to to 90 percent of asteroids that come close to the Earth at least 140 meters in size. The world’s asteroid-finding infrastructure isn’t able to complete even the 140-meter goal, according to a National Academies report released earlier this year. As of yet, scientists only know of about 30% of the estimated 25,000 asteroids that fulfill the congressional mandate. There isn’t adequate infrastructure yet. 

2019 OK would have been below that limit. 

This is scary, and reinforces the need for a better detection network.

Don't forget that in 2013, an asteroid about the size of a house exploded over the Russian city of Chelyabinsk. The shockwave broke almost every window in the city and injured more than 1,000 people.