On August 28, 2016, the Earth missed what could have been a doomsday scenario. A large asteroid passed between the Earth and the Moon undetected, coming within 100,000 km (60,000 miles) of Earth, less than a quarter of the distance between Earth and Moon. How did such a killer asteroid go undetected?
The potentially Earth-killing asteroid was detected by the International Astronomical Union’s Minor Planet Centre (MPC) and was named 2016 QA2. The IAU estimated the deadly space missile to be between 16 and 42 meters across (~50-140 ft) and hurtled past Earth at around 1500 kilometers a minute, or around 56,000 miles per hour.
It's terrifying to think about, but asteroids like 2016 QA2 pass close to Earth undetected all the time. Due to this asteroid’s particularly unique orbit, it was impossible to determine that it would pass so close to Earth until it actually flew just above our heads, astronomically speaking.
NASA has detected and is tracking around 15,000 “near-Earth objects” (NEOs) such as this asteroid. A near-Earth object is any small object in space with an orbit that passes close to Earth, such as comets and asteroids. To date, 874 of the NEOs NASA tracks are classified as asteroids with a diameter of 1 kilometer or larger, and 1728 of these NEOs have been deemed as Potentially Hazardous Asteroids (PHAs). Don’t worry, though, according to NASA’s Jet Propulsion Laboratory, that doesn’t mean that Earth is in any imminent danger:
This “potential” to make close Earth approaches does not mean a PHA will impact the Earth. It only means there is a possibility for such a threat. By monitoring these PHAs and updating their orbits as new observations become available, we can better predict the close-approach statistics and thus their Earth-impact threat.
A solar system full of potential doomsday scenario asteroids whizzing around space undetected, you say? Oh well, I didn’t want to sleep tonight anyway.