On a quiet morning on Feb. 15, 2013, a meteor entered the Earth’s atmosphere at a speed of 40,000 miles per hour (11 miles per second), exploding over Chelyabinsk, Russia with a reported force of 30 atomic bombs. In fact, the shockwave was allegedly so intense that people reported damage up to 75 miles away from the meteor’s explosion, which occurred about nine miles above sea level.

Hundreds of studies have been written since then, but scientists are still trying to figure out where it came from, and how it went undetected. It’s not like the rock itself was particularly big—about 65 feet—but it continues to leave a mark. Upon its atmospheric entry, the explosion generated a superbolide that scientists say was brighter than the sun; some eyewitnesses at the time reported feeling an intense heat from the fireball.

It must have truly felt like the end of the world.

About 1,500 people were injured due to broken glass and other debris, though no deaths were reported. Although scientists have an idea of where the Chelyabinsk meteor came from, they’re still not 100 percent sure. To that end, researchers also aren’t sure if it’s part of a larger threat. Following the event in 2013, one researcher said, “If humanity does not want to go the way of the dinosaurs, we need to study an event like this in detail.”

The bad news is rocks the size of the Chelyabinsk meteor are undetectable from Earth, which means a similar event could happen at any time.

“Another body of this size could hit Earth without warning in the future,” said Jiri Borovicka, as astronomer at the Academy of Science of the Czech Republic.