“This example shows that in the absence of traffic rules and communication protocols, collision avoidance depends entirely on the pragmatism of the operators involved,” said Holger Krag, Head of Space Safety at ESA, in a statement.

Already, stress fractures have appeared in the global system that keeps satellites from colliding. Last week, the European Space Agency announced that it boosted its Aeolus satellite into a higher orbit to avoid a collision with a recently-launched SpaceX satellite, Starlink 44, just one of a possible 12,000 satellites that could fly under Elon Musk's banner by 2020. SpaceX initially rebuffed the agency's warning of a possible collision, and blamed a software bug for not receiving updated figures from the U.S. military that might have spurred the American company to coordinate with the European agency.

In a few years, there could be ten times as many artificial satellites in low-Earth orbit alone (the band of space where the International Space Station resides) thanks to private companies that have proposed launching spacecraft to deliver services such as beaming the internet down from space. That huge influx of corporate satellites is going to complicate things in space, where there are effectively no traffic rules—like a highway with no cops and everyone driving blindfolded.

More than 1,300 active human-made satellites are flying in low orbit right now. They ceaselessly glide, boosting up and down to avoid bits of space junk and occasionally each other in a robotic ballet hundreds of miles above their human controllers.

Although the possibility of two satellites colliding above our heads seems new and rather frightening, it has happened before. The first-ever recorded collision between two human-made satellites occurred 10 years ago, in 2009, and drastically changed how the world approaches space traffic management and debris mitigation.

With even more urgent shifts on the horizon, a writhing rat-king of deeply human issues need to be worked out to avoid an anthropogenic tragedy in the void: a cascading band of debris that renders a swath of space effectively unusable.

What happens when two satellites collide?

On the evening of February 13, 2009, the National Weather Service in Jackson, Kentucky received calls from people reporting possible explosions and earthquakes.

According to a bulletin from the National Oceanic and Atmospheric Administration (NOAA), the feds advised local law enforcement that the loud booms and flashes of light in the sky in Kentucky were likely the result of debris from a collision between two satellites 500 miles above Siberia three days prior, on February 10. It was the first recorded incident involving two artificial satellites slamming into each other in orbit.

The spacecraft in question were an active Iridium 33 satellite—operated by U.S.-based Iridium Communications LLC—and Kosmos 2251, a decommissioned Russian satellite. According to a 2009 article by Brian Weeden, director of program planning for the Secure World Foundation and former instructor in the Air Force's orbital analyst training program, the satellites were travelling at slightly different inclinations but their orbits intersected at a nearly 90-degree angle close to the North Pole. Orbits intersecting isn't uncommon, Weeden said in an interview, but satellites colliding is incredibly rare.

"We tend to think of the probability as astronomically low, and it is pretty low, but given enough rolls of the dice it will eventually happen."

The finer details of what led to the collision are still unclear a decade later, Weeden said, which speaks to the messy realities of observing and controlling objects hundreds of miles away using math (playing "billiards in space," as Weeden put it in his article). The uncertainties and communication breakdown that led to the ESA thrusting out of the way of a Starlink satellite is a reflection of these difficulties.