In a chilling reminder of our planet’s vulnerability, a massive asteroid the size of a 10-story building slipped silently between Earth and the Moon on January 8, 2017, undetected until it was almost too late. Now designated 2017 AG13, this cosmic intruder was only spotted on Saturday by the Catalina Sky Survey, leaving astronomers and experts scrambling to track its trajectory as it barreled through space at a staggering 16 kilometers per second.
“This object was moving fast and dangerously close,” said Eric Feldman, an expert with astronomy news website Slooh, during an urgent live broadcast of the fly-by. The asteroid, measuring approximately 25 to 35 meters in diameter, came within a mere 0.5 lunar distances—roughly half the distance between Earth and the Moon. For perspective, that’s a cosmic hair’s breadth in astronomical terms.
The parallels to a catastrophic event in 2013 are striking. Feldman noted that 2017 AG13 is roughly the same size as the meteor that exploded over Chelyabinsk, Russia, unleashing a shockwave that shattered windows, damaged buildings, and injured over a thousand people with flying glass and debris. If 2017 AG13 had collided with Earth, it could have unleashed an explosion equivalent to 700 kilotons of TNT—35 times the power of the Nagasaki atomic bomb.
What makes this event even more unsettling is that it went unnoticed by global warning systems until just days before its approach. The asteroid’s orbit, which also crosses the path of Venus, underscores the unpredictable nature of near-Earth objects (NEOs). These celestial wanderers, ranging from a few meters to several kilometers in size, can be made of ice, rubble, or even nearly pure metal, making them difficult to detect and track. Their varying brightness and orbits only add to the challenge.
4 This diagram shows just how close the space rock came to Earth
4 If the asteroid had hit our planet, it would have exploded with a force equivalent to about 35 of the nuclear bombs which destroyed Nagasaki
The incident highlights the gaps in our planetary defense systems. The Near-Earth Object Camera (NEOCam), an infrared telescope designed to detect asteroids like 2017 AG13, is built to spot objects twice its size but recently received only partial funding from NASA. This leaves Earth’s monitoring capabilities stretched thin. According to The Planetary Society, only 60 percent of near-Earth objects larger than 1.5 kilometers have been identified, and the number of smaller, yet still dangerous, objects like 2017 AG13 is exponentially higher.
Just last month, the U.S. White House released a Near-Earth Object Preparedness Strategy, acknowledging the need for improved detection and response capabilities. The document calls for better integration of national and international assets to address the threat of NEO impacts. Yet, as 2017 AG13 demonstrates, early warning remains a critical weak point.
While the chances of a “potentially hazardous” asteroid striking Earth in the next century are estimated at just 0.01 percent, the stakes are too high for complacency. With roughly five new asteroids discovered daily, the race to bolster our defenses is more urgent than ever. The silent passage of 2017 AG13 serves as a stark wake-up call: the next cosmic threat could be closer than we think, and our ability to see it coming is far from guaranteed.