(UPDATE: The rocket booster stage that will hit the moon on March 4th is not a SpaceX upper stage as first announced. It is instead a Chinese booster from the Chang’e 5-T1 lunar mission, launched in 2014. For more details, click here.)

HERTZSPRUNG CRATER (WHTM) — If all observations and calculations are correct (and there’s no reason to believe otherwise) a SpaceX Falcon 9 upper stage will crash into the Hertzsprung Crater on the far side of the moon on March 4 at about 12:25:58 Universal time, or 7:25 a.m. EST.

Should we worry? According to Bill Gray, who announced the event, the answer is no.

Gray runs Project Pluto, a company supplying software for professional and amateur astronomers.

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He also tracks space junk. With the help of a lot of other observers, he put together the track of the SpaceX rocket, and announced the impending collision on his website on January 21.

The SpaceX Falcon 9 rocket in question launched from Cape Canaveral on February 11, 2015. Its payload-the Deep Space Climate Observatory (DSCOVR). The two stage rocket delivered the satellite to Lagrange point 1, a million miles from Earth. SpaceX was able to bring the first stage back to Earth, but the second stage didn’t have enough fuel to return. It ended up in an elliptical orbit sending it out beyond the orbit of the Moon, back to the vicinity of Earth, back beyond the Moon, and so on.

“Most” objects will orbit in ellipses.” writes Gray in his web post. “This one sort of orbits the earth in an elongated ellipse, but the effects of the moon perturb it so that there have been gradual (and sometimes sudden) changes ever since it was launched in 2015.”

According to Gray the rocket passed close by the Moon on January 5th. It passed close enough that the Moon’s gravity “nudged” it into a different orbit. It will make one more pass by Earth in early February, travel out past the Moon’s orbit for the last time, then crash into it on March 4.

There are uncertainties, of course, the main one being, of all things, sunlight. Sunlight out in space actually exerts pressure on objects. The rocket stage is tumbling, which means it’s being pushed by sunlight unevenly.

“These unpredictable effects are very small. But they will accumulate between now and 2022 March 4.” writes Gray. But he also notes the effects will be minor. “At a guess, the above prediction may be wrong by a few kilometers and second from the predicted time.”

Should we worry this impact will affect the Moon’s orbit? Gray notes in his post “Keep in mind that this is a roughly four-ton object that will hit at 2.58 km/s. The moon is fairly routinely hit with larger objects moving in the ballpark of 10-20 km/s; hence, the craters. It’s well-built to take that sort of abuse.”

(The Moon masses 73,430,000,000,000,000,000 metric tonnes or 80,730,000,000,000,000,000 US tons. Being in orbit, it doesn’t weigh anything. But whether you look at it as mass or weight, a measly little four-ton rocket stage isn’t going to do the Moon much damage.)

In fact, humanity has been deliberately smacking things into the Moon for decades. In the early 1960s NASA sent up nine Ranger spacecraft which were designed to deliberately impact on the Moon’s surface. (Most of them failed.) And during the later Apollo Moon Missions, the SIV-B boosters, the third stage of the Apollo rockets, were intentionally crashed into the Moon. As Gray explains in his post:

“Earlier missions had left seismometers behind; the impacts made “moonquakes” with a well-determined amount of energy at a precisely known time. That helped to calibrate the seismometers. Fifty years later, the moon has remained in its orbit.”

In fact, according to Gray the most unusual thing about this impact is it’s happening by accident.

“This is the first unintentional case of which I am aware.” he writes.

To visit Project Pluto, click here.

To see the full announcement of the impact, click here