Scientists and government agencies have been concerned about space junk around Earth for decades. But humanity’s stellar ambitions extend far beyond the confines of Earth’s orbit. Since the 1960s with the launch of the Apollo program and the emergence of the space race between the US and the Soviet Union, people have also left trash around the Moon.
Currently, experts estimate that there are several dozen space debris like rockets, dead satellites and debris related to missions orbiting in cislunar space – the space between the Earth and the Moon and the area around the Moon. Although this is not yet a large amount of junk, astronomers have very little information about where space debris resides, let alone what it is and how it got there.
I am a planetary scientist and also run the Center for Space Safety, Security and Sustainability at the University of Arizona. As the focus of space activity becomes the Moon, with every future mission the debris will be left in cislunar space. This waste is an emerging problem that could create dangerous conditions for future astronauts and spacecraft.
My colleague Roberto Furfaro and I hope to help prevent this problem. Together, we are using telescopes and databases on lunar missions to find, describe and track lunar space debris and build the world’s first catalog of cislunar space objects.
Abandoned and potentially dangerous
Historically, NASA and the US military have not tracked space debris from dozens of crewed and robotic missions to the Moon. There is no international agency monitoring lunar objects. This lack of oversight is why scientists do not know the location or orbit of the majority of lunar space debris. And these objects will not disappear – in near empty space, whatever remains in orbit around the Moon or in cislunar space will remain there for at least decades.
The lack of information about man-made objects orbiting the Moon poses many risks to lunar missions.
The first is the risk of collision. Humanity is at the beginning of a new wave of lunar exploration. Over the next 10 years, six countries and several commercial companies have plans for more than 100 missions. With each mission, the risk of collision with existing debris increases and so does the total amount of debris when the mission leaves the debris.
Crash landings on the surface of the Moon are also dangerous because the Moon does not have a thick atmosphere to burn falling space debris. This is dramatically demonstrated by the impact of the Chinese rocket booster that has been launched to the far side of the Moon in March 2022. My team and I finally identified the object as originating from China using a telescope built to track objects in cislunar. premises. With the US and China planning to build lunar bases in the coming years, falling debris could pose a real threat to human life and infrastructure on the Moon.
Hard to track
If you want to prevent the Moon from becoming a cosmic landfill, you need to be able to track cislunar space junk. But doing so is difficult even on a good day for two main reasons: distance and light.
Cislunar space is about 2.66 million miles from Earth — a far cry from the distance at which the US government currently tracks objects in space. But space is not just two dimensions. The three-dimensional volume of cislunar space is enormous, and any objects within it are small in comparison.
Light presents another challenge. Like the moon itself, the brightness of an object in cislunar space depends on the amount of sunlight the object reflects. During a crescent moon, lunar debris appears dim and low in the evening sky, making it difficult to spot. When the moon is full, the same objects are higher in the sky and brighter because there is more sunlight, but they merge with the bright light that surrounds the full moon. Finding an object during a full moon is like trying to find the faint glow of a firefly next to a bright searchlight. In the glare of the moon is the Cone of Shame, so named because it is difficult to track objects within it.
Curating the catalog
Due to the difficulty and lack of adequate resources to track objects near the Moon, no group or organization has consistently pursued it. So, in 2020, Furfaro and I took on the challenge of finding, tracking and cataloging man-made debris in cislunar space.
First, we link historical observations from various telescopes and databases to each other to identify and confirm what cislunar objects are known. Then, realizing that there was no special telescope that searched the night sky for cislunar objects, my students at the University of Arizona and I built one. At the end of 2020, we finished building a 24-inch (0.6 meter diameter) telescope, located at the Biosphere 2 Observatory near Tucson.
The first object tracked was Chang’e 5, China’s first lunar sample return mission. A large rocket launched on November 23, 2020, headed for the Moon. Despite the intense glare of the moon, my students and I were able to track Chang’e 5 12,354 miles from the Moon, deep within the Cone of Shame. With this success, we started tracking the newly launched cislunar payloads and adding them to our new catalog. With this success, we started to track newly launched cislunar payloads in order to calculate and predict their orbits to prevent them from disappearing.
To characterize old and new space debris, once we know where the object is, we use optical and near-infrared telescopes on Earth to capture the object’s spectral signature – the specific wavelengths of light that bounce off the object’s surface. By doing this, we can find out what materials are made of objects and identify them. This is how we identify the mysterious rocket that crashed into the Moon in 2022. We can also measure changes in the light bounced off the object over time to determine how fast the object is rotating, which can also help with identification.
Over the past two years, we have gotten better and better at finding and identifying objects in cislunar space. While we were first excited to spot the Chang’e 5 spacecraft the size of a school bus, now we can track CubeSats no bigger than a cereal box – like NASA’s Lunar Flashlight.
So far, my team has been able to identify several dozen pieces of debris in cislunar space and continue to add to the ever-growing catalog. Most of the work ahead includes continuous observation and matching of objects to known missions to confirm whether the object is out there and where it came from.
While there is still a long way to go, this effort is designed to eventually become the basis for a catalog that will help make safer and more sustainable use of cislunar orbital space as humans begin their expansion from Earth.
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