Another asteroid made a close pass to the Earth, on January 24, at 11:54 EDT (5:54 UTC), the second one to do so in as many weeks. Asteroid 2017 BX’s close pass — just within the Moon’s orbit — follows asteroid 2017 AG13’s January 9 flyby by a mere 15 days. While this new asteroid missed us as well, and wouldn’t cause much damage if it were to actually to have hit us, it does set up a disturbing trend, as both 2017 BX and 2017 AG13 weren’t discovered until mere days before their closest approaches.

2017 BX wasn’t spotted until January 20, only four days before its closest approach. Its predecessor, 2017 AG13, gave even less warning, having been spotted only two days prior to its own close pass. These two events underscore the difficulty faced by sky survey programs in discovering potentially dangerous asteroids — large ones are easy to spot, but smaller ones can go completely unnoticed until they’re right on top of us, remaining undetected by virtue of both their miniscule size and dark coloring. It does make one wonder how many of these rocks we didn’t see before astronomers started looking for them…

Thankfully, 2017 BX is not only smaller than 2017 AG13, but it also missed us by a slightly wider margin than the January 9 flyby: size estimates for 2017 BX are between 6.6 to 15 meters (22 to 50 feet) across, somewhere between the size of a car and a bus, and is only traveling at half of its predecessor’s speed, at 7.4 meters per second (4.6 miles per second), a little slower than the International Space Station. Its closest approach is also 270,000 km (167,770.222 miles) away, a little over three-quarters of the distance to the moon, as compared to 2017 AG13’s 192,500 kilometer (119,500 mile) flyby.

Thankfully, if 2017 BX were to strike the Earth, its relatively slow speed and small size means the energy of its impact would only be around 10 kilotons of TNT, or two percent of the half-megaton explosion released by the meteor that exploded over Chelyabinsk, Russia, in 2013.