A SpaceX rocket slamming into the Moon is a reminder to clean up our deep space junk

For the last seven years, a piece of an old Falcon 9 rocket has been circling the Earth on a very wide path. On March 4th, this rocket piece is predicted to slam into the far side of the Moon. It is a reminder that we need to take better care of our deep space junk, according to the astronomer who first figured this out.

The doomed component was part of a rocket that was launched in February of 2015. The satellite lofted by the vehicle is called DSCOVR and is used by the National Oceanic and Atmospheric Administration to better predict space weather. In order to perform its job properly, DSCOVR was designed to be very far away from Earth. The upper stage or second stage of the rocket lofted the vehicle up to an incredibly high altitude above Earth to get the satellite out there. The upper stage was abandoned after the satellite was deployed and left in an elliptical path around the planet.

The upper stage is going to coincide with the moon after seven years. It is not the first time that a human-created object has collided with the Moon's surface: NASA has sent rocket parts and spacecraft careening into the lunar dirt before. The first piece of space junk to make a dive bomb onto the Moon may be the Falcon 9. While this won't cause any problems for our planetary satellite, the incident serves as a reminder to the space community that we may want to come up with better ways for disposing of our space trash.

Bill Gray, an astronomer and asteroid tracker running Project Pluto, says that junk of this sort would be better handled.

Ars Technica reported earlier this month that Gray was the first to figure out that the Falcon 9 would hit the Moon. He is one of the few people who has been following the rocket fragment. He and other amateur space trackers with telescopes and cameras have been periodically observing an object for a couple of weeks or months. After each observation, Gray would update the stage's projected path around Earth using a software program he's developed over the last two decades for his company. The software used to predict the location of asteroids and tiny moons around gas giants. He uses the software to track the stuff humans have created around Earth.

The path of the Falcon 9 has been difficult to determine over the years. Space junk can absorb sunlight and re-radiate it into space. It is difficult to predict where the object will go over the long term because of the gentle force that can push it off its path. On January 5th, the stage made a close flyby of the Moon, and the gravity from that can slightly affect the orbit.

Image: Bill Gray/Project Pluto

There were some small uncertainties about the collision course at first. Gray and others have a good idea of what will happen. After the second stage reaches its most distant point on its elliptical path, it will fall back toward the Earth and cross paths with the Moon. It will hit the far side of the Moon at 7:25AM on March 4th, moving at 2.58 kilometers per second. The impact should create a crater up to 20 meters in diameter. Astronomers will be able to see the exact angle and location of the impact in early February.

It's a dead rock that we've thrown a lot of objects at before, so there's no reason for us to fear that this will harm the Moon. During the Apollo missions, we crashed various rocket stages into the lunar surface, and both the US and Russia have sent plenty of spacecraft to the lunar ground in pursuit of winning the space race. During the LCROSS mission in 2009, NASA crashed objects into the Moon in order to see what was underneath.

The impact of the Falcon 9 may allow NASA to see what is underneath the surface. Gray wants to see the aftermath of NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan-2.

Gray thinks that the collision is a good reminder that we need to have better protocols for disposing of space junk. The International Space Station and satellites can be threatened by pieces left in lower orbits. The second stages of the rockets will be thrown away when they go to lower altitudes. On those occasions, the object will be directed towards the Earth at a very low angle so that it burns up in our atmosphere. It's unlikely any large pieces will survive the break up, and those that do will fall over unpopulated areas.

Sometimes the rocket stages will be left out in the wilderness after the launch for missions that go to the Moon. The Ariane 5 second stage that carried NASA's new space observatory, the James Webb Space Telescope, remained in space and is now in the Sun, Gray says. A billionaire currently in the vicinity of the Sun sent a car to Mars, though it was sent there on purpose. Most space agencies and official tracking entities don't keep tabs on these objects.

When junk is abandoned in higher altitudes, it can still be an issue. If these objects were to come back and hit our planet, they would come in much faster and at a higher angle to the atmosphere. It is more likely that certain pieces will survive the re-entry.

Such events are rare and don't pose a real threat to people at the moment. Gray says he and others tracked a piece of space junk that entered the atmosphere over Sri Lanka in 2015, as well as two Chinese lunar rocket stages that reentered over the Pacific Ocean. He argues that we might want to dispose of these stages on the Moon rather than letting them hit Earth. We could get some scientific value out of crashes if we knew where they were headed.

It's better to slam into the Moon than it is to slam into the Earth, says Gray.