On March 4, humanity will set a trash record when an old rocket booster crashes into the far side of the Moon. It will be the first time that a piece of man-made space debris has hit a celestial body other than Earth without being directed at it.
The booster is likely part of a rocket that launched a small Chinese spacecraft, called Chang’e 5-T1, to the Moon in 2014. Although Chang’e 5-T1 successfully returned to Earth, it is believed that the propellant flew away. chaotically in space ever since. Lunar gravity is now bringing it closer and will soon drag it into a fatal collision with the far side of the Moon. The crash should produce a puff of debris and leave behind a small crater.
The incident poses no immediate danger to humans or other spacecraft, but with at least half a dozen craft expected to reach the Moon this year, concern is growing that the lunar surface will become a involuntary dump.
“Public opinion has shifted enough in recent years that even a deliberately crashing scientific lunar orbiter would still raise questions about the impacts on the lunar environment, in a way it would not have done before,” says Alice Gorman, space archaeologist at Flinders University. in Adelaide, Australia.
Many other spacecraft – and parts of spacecraft – have hit the Moon (see ‘Moon crashes’). The first was the Soviet Union’s Luna 2 in 1959, which became the first man-made object to come into contact with another celestial body when it crashed just north of the lunar equator. . The most recent was China’s Chang’e 5 lander (a different spacecraft from Chang’e 5-T1), which dropped an ascent vehicle on the Moon in 2020 as it returned lunar samples to Earth .
Many man-made lunar impacts have been intentional mishaps to terminate lunar orbit missions that have run out of fuel. Some have involved planned Moon landings, successful or not. Others were for scientific purposes, such as when NASA launched parts of large Saturn rockets onto the lunar surface during the Apollo mission era in the late 1960s and 1970s, to study how seismic energy impacts reflected on the Moon.
But never before has a piece of long-lived space junk – the propellant will have been circulating in space for more than seven years – collided with the Moon.
The problem of space debris is well known for the region around the Earth. More than 12,000 Earth-orbiting satellites have been launched since the start of the space age in 1957, and about 5,100 of them are still operational, according to the European Space Agency. In total, the agency estimates that there are more than 36,000 pieces of debris more than 10 centimeters in diameter circling Earth’s orbit. These include dead satellites, as well as remnants of previous launches and tests of anti-satellite missiles.
Around the Moon, space is less crowded, but lunar scientists fear it will remain so. A research team led by Vishnu Reddy, a planetary scientist at the University of Arizona in Tucson, uses telescopes to regularly track the positions of more than 150 objects in space around the Moon. Of that, at least 90% is trash, Reddy says.
He and his colleagues tracked the object which is about to hit the Moon. They analyzed how sunlight reflects on it to confirm that it is made of a material similar to Chinese rocket propellant. (The object was originally identified as a SpaceX rocket booster, but analysis showed its properties did not match that craft.)
Astronomers won’t be able to observe the impact from Earth in real time, as the collision will take place on the far side of the Moon, likely in or near a crater named Hertzsprung. But several spacecraft in lunar orbit will try to spot it or its aftermath.
Previous Moon impacts have generated small plumes of material. In 2009, NASA’s LCROSS probe crashed into a dark crater near the lunar south pole, kicking up a cloud of dust that was confirmed to contain water. Water and ice are scarce on the moon, but the upcoming crash is unlikely to contaminate lunar ice, says Parvathy Prem, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland.
There are no significant international restrictions on what can be dropped on the surface of the Moon. In 1999, NASA crashed its Lunar Prospector spacecraft carrying the ashes of planetary geologist Gene Shoemaker, an act the Navajo Nation has criticized as callous and sacrilegious. In 2019, Israel’s private lunar lander Beresheet accidentally crashed, spilling cargo including resistant organisms known as tardigrades onto the lunar surface. A growing number of researchers are also concerned about the integrity of the lunar environment, Gorman says; last year, a group drafted the first Moon Bill of Rights.
How the Chinese booster ended up on a trajectory to hit the Moon is not entirely clear. The gravity of the Earth and the Moon exerts it since its launch. Bill Gray, a Maine astronomer and space tracker who spotted the next collision, notes that there is no organization tasked with tracking distant objects in space. The US Space Force tracks space objects in geostationary orbits, about 35,800 kilometers from Earth – but the Moon is almost 400,000 kilometers away. Remote tracking is therefore in the hands of individual groups, such as Reddy’s.
“The information the public relies on does not come from official government sources,” Gorman said. “It’s positive because it shows that people are able to monitor the space environment themselves, but worrying because it reveals gaps in what is known and who is responsible.”