A bus-sized asteroid passed by the Earth at a distance closer than the moon Saturday — but the more disconcerting part is how little warning astronomers had of the event.

Scientists learned of the 25-foot asteroid named 2014 HL129 just three days before it came within 186,000 miles of Earth.

The asteroid was spotted by astronomers with the Mt. Lemmon Survey, located in the Catalina Mountains of Arizona.

Watch this animation of HL129′s trajectory:

Though Saturday’s event was only a close shave, incidents like the 65-foot-wide meteor that crashed in Russia in February 2013 — which went undetected until it was too late — are why NASA and other government space agencies around the world are working to better predict these giant space rocks that can have catastrophic consequences.

NASA’s Near-Earth Object Program estimates that more than 90 percent of the near-Earth objects larger than one kilometer have already been discovered, but 90 percent of those 140 meters or larger are still being tracked down.

Last year, NASA announced the Asteroid Grand Challenge, which encouraged the general public to get involved in the various aspects of asteroid hunting. Watch NASA’s video about this project:

But what’s to be done if a threatening asteroid is found? NASA is working on ideas to take care of that problem, too. One option includes sending up a weighted robotic spacecraft to collide with the object to send it off course, but this would require years of prior warning. Other ideas involve nuclear explosions or a spacecraft that could serve as a “gravity tractor” and change an asteroid’s velocity just enough to avoid a collision with the planet.

NASA’s Near Object Program has more detailed information about HL129.

(H/T: SlashGear)

Front page image via Shutterstock.

This story has been updated.