Two astronomers are working to track space junk around the Moon

With over 100 lunar missions anticipated in the upcoming years, space debris around the Moon may provide a problem for humanity.

Government organizations and scientists have been concerned about the space debris orbiting the Earth for decades. But humankind's aspirations for the stars go beyond the region of space immediately around the planet. People have been dropping rubbish all over the Moon since the 1960s, when the Apollo program was started and the space competition between the US and the USSR began.

The area between Earth and the Moon and the region around the Moon is known as cislunar space, and scientists believe that there are a few dozen pieces of space junk, such as spent rocket bodies, abandoned satellites, and mission-related debris, circling there right now. Even though there isn't much trash at the moment, astronomers know very little about the location of these objects in space, let alone what they are or how they got there.

I am a planetary scientist and the director of the University of Arizona's Space Safety, Security, and Sustainability Center. The amount of debris left in cislunar space will increase with each new mission as space operations shift their attention to the Moon. In the future, this trash, which is a rising issue, may pose a risk to astronauts and spacecraft.

Together with my coworker Roberto Furfaro, I'm trying to stop this issue from getting out of hand. In order to identify, characterize, and monitor lunar space debris and create the first catalog of cislunar space objects in the world, we are working together to use telescopes and existing databases on lunar missions.

Unoccupied and maybe unsafe

NASA and the U.S. military haven't historically kept a close eye on space debris from the countless crewed and robotic trips to the Moon. Additionally, there is no worldwide organization that has kept track of lunar objects. The great majority of lunar space junk is unknown in terms of location and orbit due to a lack of supervision. And these items won't just disappear; in the almost complete vacuum of space, anything still in lunar orbit or in cislunar space will probably stay there for at least a few decades.

The hazards associated with lunar missions are many because to the lack of knowledge about human-made objects circling the Moon.

Collision danger comes first. We are at the start of a new phase in lunar exploration for humanity. Six nations and a number of private organizations have plans for more than 100 missions during the next ten years. As missions leave trash behind, the likelihood of a collision with already-existing debris grows with each mission, as does the overall amount of garbage.

Because the Moon lacks a dense atmosphere that may burn up falling space debris, crash landings there are also a significant concern. This was graphically shown in March 2022 when a used Chinese rocket booster collided with the moon's far side. Using telescopes we constructed to follow objects in cislunar space, my colleagues and I were the ones to eventually determine that object's origin to be Chinese. Due to the fact that both China and the U.S. want to construct lunar bases in the upcoming years, falling debris may start to pose a serious risk to infrastructure and human life on the Moon.

Hard to find

You need to be able to track cislunar space debris if you want to stop the Moon from turning into a cosmic landfill. But even on a nice day, it might be difficult to see because of two factors: distance and light.

Cislunar space is 2.66 million miles away from Earth, a great distance beyond where the U.S. government now monitors spacecraft. However, space is three-dimensional as well. Any objects present within the enormous three-dimensional region of cislunar space pale in contrast.

Light poses still another difficulty. The amount of sunlight that an object in cislunar space reflects determines its brightness, much like the Moon does. Lunar debris is difficult to locate during a crescent moon because it appears low and faint in the evening sky. The same things seem brighter and higher in the sky during a full moon because more sunlight shines on them, but they are obscured by the full moon's dazzling glare. It's like attempting to discover a firefly's dim glimmer next to a brilliant search light when there is a full moon and you're trying to find something. The Cone of Shame, so called because it makes it difficult to track objects, is within the lunar glare.

Organizing the library

There is currently no group or organization continuously tracking objects near the Moon due to the challenge and lack of necessary resources. Furfaro and I decided to take on the task of finding, locating, and cataloging human-made junk in cislunar space in 2020.

To identify and validate which cislunar objects were already known, we started by connecting previous observations from different telescopes and databases. Then, understanding that there were no specialized telescopes for looking for cislunar objects in the night sky, my University of Arizona students and I built one. We completed the construction of a 24-inch (0.6-meter) telescope in late 2020; it is located at the Biosphere 2 Observatory outside of Tucson.

China's first lunar sample return mission, Chang'e 5, was the first object we followed. On November 23, 2020, a massive rocket was fired at the Moon. My classmates and I were able to follow Chang'e 5 to a distance of 12,354 miles from the Moon, deep within the Cone of Shame, despite the intense lunar glare. Following this achievement, we began monitoring recently launched cislunar payloads and cataloguing them for our infant database. After achieving this feat, we began monitoring freshly launched cislunar payloads in order to determine and forecast their orbits and keep them from straying.

After determining an object's location, we utilize optical and near-infrared telescopes on Earth to collect the object's spectral signature, or the particular wavelengths of light that reflect off an object's surface. By doing this, we can identify an item and determine what material it is comprised of. This is how we were able to locate the unidentified rocket booster that struck the moon in 2022. In order to estimate how quickly an item is spinning, we may also monitor variations in the light reflecting off the object over time. This can aid in identification.

We have become steadily better at discovering and recognizing objects in cislunar space during the past two years. While initially we were pleased to locate the Chang'e 5 spacecraft, which was about the size of a school bus, we can now follow CubeSats that are only about the size of a cereal box, like NASA's Lunar Flashlight.

My team has so far been successful in locating a small number of debris objects in cislunar space, and we are working to add to this ever-growing collection. To establish what objects are present and their origins, the majority of the task ahead entails continuing observations and matching items to known missions.

Even though there is still a long way to go, these initiatives are intended to serve as the foundation for a catalog that will eventually assist ensure a safer, more sustainable use of cislunar orbital space as mankind starts to expand beyond the Earth.