A piece of space junk the size of a school bus is barreling straight toward the moon

A piece of space junk from a SpaceX rocket launch in 2015 is hurtling toward the moon, and is set to crash into the lunar surface on March 4, astronomers have predicted.

The piece is part of a Falcon 9 rocket that launched from Florida in 2015. The purpose of the mission was to send the DSCOVR Space Weather Satellite into space, approximately one million miles away from earth.

But seven years later, the upper stage of the rocket booster remains tumbling through space. It was too far away from Earth and had too little fuel to return, so instead, it's been yanked around by the Earth and the moon's gravitational pull in what experts say is a "chaotic" orbit.

"It's almost like a billiard ball bouncing off of other billiard balls," Bill Gray, an independent astronomer who first discovered that the Falcon 9 piece would hit the moon, told NPR.

In other words, the path of this piece of space junk could have gone in a lot of different directions — like the many scenarios for where balls may roll when a player breaks in pool. Gray says it could have gone into an orbit where it would have hit the Earth, or it could have even been picked up into an orbit around the sun.

But in mid-January, Gray got new data that showed the rocket piece was going to crash into the moon, making it the first time — that we know of — humans have accidentally crashed something into the lunar surface.

The moon will get a new crater

The rocket piece that will crash into the moon is no small thing. It's about 12 meters the long, or the size of the school bus, and weighs four tons. It's also whizzing through space at about 5,600 miles per hour, Jonathan McDowell, an astronomer with the Center for Astrophysics Harvard and Smithsonian.

The rocket piece is "going to get completely destroyed. A huge plume of moon dust is going to go up where it hit and then settle down over a wide area of the moon," he said.

After about a day, the dust will settle and there will be a "sparkly fresh new lunar crater," McDowell said.

In the past, NASA has conducted missions to crash objects into the moon on purpose. In 2009, they sent a spacecraft called LCROSS to see if water particles would come up in the impact.

Overall, this predicted impact in March won't be a significant change to the moon, but Gray still believes there's something to learn from it.

"It could be a reasonably interesting scientific discovery that we'll be able to learn a bit about the nature of lunar impacts, how large a crater you get for a given size object and a given speed. We may also learn a certain amount about the geology of this particular part of the moon," Gray said.

Space needs to get cleaned up

While experts are tracking the path of the Falcon 9 rocket piece and what can be learned from this accidental impact, there's also a renewed conversation about how to handle the amount of space junk that's floating around.

The U.S. Department of Defense is tracking more than 27,000 pieces of space junk, including old rocket pieces and satellites. But movement on how to actually remove the junk has been somewhat stalled.

"I know the government is really taking a very close look at this at the moment," McDowell said. "People are aware that space junk is a big issue that needs to be addressed. It's just getting off the committee stage and onto the actually doing something about it stage that seems to be stuck right now."

The amount of old space junk in low Earth orbit is of particular concern.

John Crassidis, director of the Center for Space Cyber Strategy and Cyber Security at the University of Buffalo, says it's possible that within 50 years, we get to the point where there's so much debris, we won't be able to launch any more satellites.

"When objects start to collide with other objects, that's going to cause more debris ... and you get a cascading effect," he said, citing what's known as Kessler's Syndrome. "That's a big concern."

What isn't a big concern, though, is this accidental lunar crash causing any harm to people on Earth, or any major problems for the moon itself.

"It's a policy concern in the long run," McDowell said. "But this particular piece of space junk smashing into the moon... the moon's had lots of things smash into it over the years. It'll be fine."

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