Another sizable asteroid has made a close pass to Earth on May 15, making 2010 WC9 the 35th object to pass within one lunar distance in 2018 alone, and the 17th to have passed within one-half of the distance between the Earth and the Moon. Thankfully, this object wasn’t big enough–or traveling fast enough for that matter–to cause any major damage to the Earth if it had actually hit us. But what is up with the increased number of asteroids making close passes to our little blue home?

Unlike 2018 GE3’s sudden discovery last month, made mere hours before its close pass to Earth; 2010 WC9 was discovered nearly eight years ago, allowing astronomers time to accurately plot its orbit: thus authorities were confident that it would not impact the planet this time around. While at an estimated 60-130 meters (197-427 feet) in size (slightly larger than last month’s 2018 GE3); 2010 WC9 whizzed by at only two-fifths of the speed of its predecessor, meaning it would have disintegrated in the atmosphere if it had actually been on a collision course with Earth.

But why does there appear to be an ever-increasing number of near misses being made by high-speed space rocks? It turns out that these swarms have been zinging past us all along, it’s just that we’re getting much better at spotting them.

"This is not a reflection of an increased number of asteroids passing by," explains Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory (JPL), in a recent Newsweek article. "The increase in discoveries reflects our increased capabilities."

Indeed, the vast majority of the 17,446 known near-Earth asteroids have been discovered since the mid-nineties, and on top of that, fewer and fewer kilometer-sized (0.6-mile) asteroids are being discovered: statistically-speaking, this means that modern sky surveys have charted more than 95 percent of these civilization-threatening objects.  The remainder are likely in orbits that don’t come close to Earth, keeping them safely out of reach.

The focus is now primarily being made on finding asteroids that fall into the mid-sized category– those that are larger than 140 meters (460 feet) across: while these objects aren’t likely to wipe out civilizations or species, they can cause regional damage, like the injuries and property damage caused by the shockwave of the meteor that exploded over Chelyabinsk, Russia in 2013.

Although approximately 2,000 mid-sized asteroids have been identified so far, researchers estimate that there may still be another 20,000 left to be discovered.

As for 2010 WC9, its recent flyby is the closest it will come to Earth until after 2190, according to JPL’s Small-Body Database.