ESA

Lots of overheated headlines in tabloids and other publications this week have been screaming about a large, "potentially hazardous" asteroid set to pass close by Earth.

Meanwhile, a newly discovered car-size asteroid passed over 100 times closer to us on Thursday -- coming near the altitude where many man-made satellites orbit -- and hardly anyone noticed.

Asteroid 2018 BD flew by our planet at a distance of about 22,000 miles (35,406 km) at 7:43 a.m. PT, just seven hours after being discovered via the Catalina Sky Survey.

Notably, satellites in geosynchronous orbit are typically at an altitude of around 22,236 miles (35,786 kilometers). So while much smaller, 2018 BD was arguably much more potentially hazardous than the other space rock making headlines: skyscraper-size 2002 AJ129, which will pass by us on Feb. 4 at a distance of over 2 million miles, or more than 10 times the distance between the Earth and our moon.

In reality, neither asteroid poses much of a threat to life and limb. But the idea of a building-size rock labeled "potentially hazardous" making its way through our cosmic neighborhood makes for good headlines.

The thing is no one is sitting at NASA and deciding which individual asteroids make them the most nervous and thereby worthy of such a title. Instead the classification is based on simply how far away and how big the asteroid is. Roughly speaking, earning the label requires nothing more than being larger than about 500 feet (140 meters) in diameter and passing within about 4.7 million miles (7.5 million kilometers) of Earth.

That means that an awful lot of asteroids are classified as "potentially hazardous," including a number of newly discovered asteroids, which the International Astronomical Union's Minor Planet Center regularly announces via Twitter. In fact, a few dozen such rocks cruised through the inner solar system last year without incident.

2018 BD is too small to be considered for the title, and if it were on a collision course with Earth, much of it would likely burn up in the atmosphere. But its proximity to geosynchronous orbit makes it potentially more hazardous than the more distant, larger asteroids that garner attention like 2002 AJ129.

Asteroid 2018 BD discovered. Flyby Jan 18 at 17:27 UT. Dist: 0.11 LD (0.09 LD from Earth surface). Size: 1-5 m. https://t.co/H9jrTJ7xyv — Minor Planet Center (@MinorPlanetCtr) January 18, 2018

A collision with a satellite could create a whole mess of orbital space junk that then collides with other satellites. In the worst case scenario, cascading collisions could trigger something called Kessler Syndrome, which essentially cuts off our access to space and presumably has major impacts on our satellite-dependent global communications system.

Realistically though, the notion of a small asteroid like 2018 BD hitting a satellite probably shouldn't keep you up at night. Even though it's coming near the altitude of geosynchronous orbit, there's still an awful lot of three-dimensional space in that range and a collision would be quite unlikely (though certainly not impossible).

What's probably more important is to know what a potentially hazardous asteroid really is: something that astronomers think is worth watching. It's not unlike those potentially hazardous storm clouds on the horizon that have never flung a deadly lightning bolt your way. Even still, it's best to keep an eye on them.

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