While you were sleeping last night, an asteroid passed close to Earth—very close. The object is known only as 2017 BH30, and it passed within 40,563 miles of the planet. That’s closer than the orbit of the moon, which is 238,000 miles away. The troubling part here is that astronomers didn’t detect 2017 BH30 until just hours before its closest approach. Luckily, it wasn’t large enough to pose a serious risk.
Scientists estimate that 2017 BH30 is around 19-23 feet (6 or 7 meters) in diameter. That’s certainly far from planet-ending, but it could still pack a punch if it entered the atmosphere. For comparison, the 2013 Chelyabinsk meteor was just shy of 20 meters across, and it caused a spectacular explosion in the sky that broke windows and scattered fragments over a wide area. The debris from the explosion caused more than 1,000 injuries.
2017 BH30 was spotted by scientists at the Catalina Sky Survey in Tuscon, Arizona over the weekend. Not long after that, it passed by Earth at 0451 UTC (almost midnight on the east coast) on January 30th. Astronomers were able to take a snapshot of it, which you can see above. 2017 BH30 is the tiny dot at the very center indicated by the lines. It’s in a highly elliptical orbit that takes 3.8 Earth years to complete. It gets as far out as 3.84 AU (an AU is the distance between Earth and the sun) and as close as 0.81 AU. Had 2017 BH30 entered the atmosphere, it’s possible it would have disintegrated, but we can’t be sure without knowing more about its composition.
This is the closest approach of an asteroid since September, when asteroid 2016 RB1 passed within 24,000 miles of the planet. That one was a bit larger than 2017 BH30, but not by much. For an asteroid to be dangerous on a global scale, scientists estimate it would need to be at least 1 kilometer (0.6 miles) in diameter. Something a few hundred meters across could still cause extensive regional damage.
So, we didn’t exactly avert disaster when 2017 BH30 missed us, but it’s chilling to think how little warning we got of its flyby. Astronomers have identified more than 15,000 near-Earth objects, some of which are large enough to cause serious damage. It’s possible there are many more on longer orbits that have not passed by Earth recently enough to be cataloged. How soon would we notice them? Hopefully more than a few hours in advance.