"The worry is that we'll start seeing a chain reaction where all the satellites kill each other with shrapnel and space becomes unusable."
There's a decent chance that two satellites will crash into each other as they orbit the Earth today.
The two satellites, both already inactive, have a one-in-1,000 chance of colliding, CNN reports, which is a much higher chance than space agencies consider safe. If a collision is going to happen, it will occur right around 6:40 PM EST when the paths of the satellites converge — right over Pittsburgh, PA.
On its own, the destruction of two decades-old satellites that have long since stopped being useful isn't a huge deal. But if they do crash, they'll fill an already-crowded sky with hazardous debris.
"The worry is that we'll start seeing a chain reaction where all the satellites kill each other with shrapnel and space becomes unusable," astronomer Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics told CNN.
The two satellites are expected to pass anywhere within 13 to 87 meters of each other — extremely close on an astronomical scale. The odds of a collision are increased by the fact that the satellites are larger than average, per CNN.
"It isn't as unlikely as it usually is," McDowell told CNN. "We start getting worried when it's one in 10,000, so one in 1,000 is unusual and it might actually be a lot worse than that."
READ MORE: Two dead satellites might collide above the US today [CNN]
More on collisions: SpaceX Wouldn’t Move Its Satellite to Avoid a Collision, Says ESA