While most of us were sleeping last Sunday morning, Earth had a close call with an asteroid that had been detected a mere 21 hours before it zipped past.
As Live Science’s Elizabeth Howell writes, the asteroid, officially known as 2018 GE3, was about the size of a football field, measuring between 157 and 361 feet in diameter. At its closest point to Earth, it passed by some 119,500 miles away—about half the distance between the Earth and the moon.
First observed at Catalina Sky Survey in Arizona on Saturday, April 14, it flew closest to Earth in the wee hours of the following morning at 2:41 A.M. E.D.T. The asteroid was zipping along at 66,174 miles per hour, Eddie Irizarry reports for Earth Sky.
The asteroid is much larger than many of the other space rocks that have passed by or exploded over Earth, causing some curiosity about how it went undetected for so long. After all, asteroids do have the potential to wreak havoc on Earth.
Asteroid 2018 GE3 flew past us today, half the distance to the Moon. Around 50-100 m in diameter, it was several times the 2013 Chelyabinsk meteor, around the size of the 1908 Tunguska event ~ easily enough to destroy a city. We had less than a day's warning. (photo credit: Michael Jäger) pic.twitter.com/kElrxBiUoB— Andrew Rader (@marsrader) April 16, 2018
A meteor that blew up over Chelyabinsk, Russia, in 2013, for example, resulted in nearly 1,500 injuries and thousands of buildings damaged. But the fragments of space rock didn’t directly hit anyone. Rather, as Katherine Hignett reports for Newsweek, experts believe the explosion caused a shockwave, and this resulted in shattered windows and damaged buildings.
Asteroid 2018 GE3 is actually three to six times the size of the Chelyabinsk meteor and roughly equal to the size of the space rock that exploded over Tunguska in 1908.
In fact, 2018 GE3 is one of the largest asteroids ever to come in such close proximity to Earth, Eric Mack reports for CNET. Larger asteroids flew by in closer proximity in 2001 and 2002, according to NASA’s near-Earth object observation database. But this is pretty rare. Asteroids of this size only approach Earth only once or twice a year.
So how did astronomers miss the asteroid until hours before flyby?
As Howell explains, asteroids are difficult to spot and track, since most are dark and generally much smaller than 2018 GE3. This means that they may not reflect enough light for telescopes to easily detect. “A telescope needs to be looking in just the right area, at the right time, to catch it,” she writes.
Many telescopes would have to be on the lookout at once to spot incoming space rocks. Though NASA does track potential threats in this manner, their current focus is tracking the most dangerous of these asteroids: space rocks at least 460 feet wide that will come within 4.65 million miles of Earth. 2018 GE3 is around 75 percent that size.
As Mack reports, another asteroid, 99942 Apophis, is set to pass by in 2029. As Smithsonian.com previously reported, this asteroid will become the closest flyby of its size. It will come as close as 19,400 miles from Earth.
But don’t worry: The chances of it actually hitting Earth are slim. And scientists have been working toward better preparation for such a disaster. Last month, researchers announced plans for a spacecraft called HAMMER that would collide and knock incoming asteroids in another direction or simply blow them up into tiny pieces, Space.com reported.
This, however, would require early detection.