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Urgent action is needed to curb space pollution around Earth.
With the number of satellites expected to increase by over six times by 2030, there are calls for a new treaty to prevent the issue from becoming too big to handle.
There's an increasing lack of space in space.
Since the world's first artificial satellite, Sputnik 1, was put into orbit in 1957, thousands more have been launched. There are now estimated to be over 9,000 satellites in orbit, and could be as many as 60,000 by the end of the decade.
The increasing number of satellites, particularly those in the commercially valuable low Earth orbit (LEO), mean that the risk of collision is rapidly rising. Impacts between satellites risk knocking out vital services, and could even start a chain reaction which would make large parts of Earth's orbit unusable.
Now, a letter published in the journal Science argues that countries and corporations urgently need to start cleaning up after themselves in space. They've called for a new international treaty, similar to the High Seas Treaty agreed in the past week, to ensure this becomes a reality.
Dr Imogen Napper, the lead author of the letter, says, 'The issue of plastic pollution and many of the other challenges facing our ocean are now attracting global attention. However, there has been limited collaborative action and implementation has been slow.'
'We are now in a similar situation with the accumulation of space debris. Taking into consideration what we have learnt from the high seas, we can avoid making the same mistakes and work collectively to prevent a tragedy of the commons in space. Without a global agreement, we could find ourselves on a similar path.'
At this very moment, there is around 10,700 tonnes of material orbiting above our heads, which is roughly the same mass as the Eiffel Tower. This is made up of many different objects, including thousands of satellites, two space stations and rocket components.
But the number of objects is continually increasing. Companies such as Starlink and OneWeb are launching thousands of satellites as part of constellations to build new communication networks.
As space becomes more crowded, satellites and space stations are having to move to avoid each other in orbit. While large objects like these are easily tracked, there are many smaller ones which are much harder to spot.
At the time of writing, the European Space Agency (ESA) estimates there are around 36,500 fragments in space larger than 10 centimetres in size. These can be caused by accidental malfunctions, micrometeorites and even missile strikes.
This debris is only the tip of the iceberg, however. While space agencies try to keep track of as many of these fragments as possible, they can't keep track of them all. Anything below a centimetre in diameter in LEO can't be detected from Earth, so numbers of these objects have to be estimated using modelling.
The ESA calculates that there could be as many as a million fragments between one and 10 centimetres in size, and up to 130 million objects over a millimetre.
The letter in Science claims that, in total, there could be as many as 100 trillion pieces of debris orbiting the Earth, moving at up to 28,000 kilometres per hour.
While all space debris will eventually fall back to Earth, this process could take centuries, depending on their orbit.
Because the smallest orbital debris can't be tracked, spacecraft such as satellites are given shielding to try and prevent damage. But even with shielding these fragments can still do a lot of damage.
Satellites can have holes punched in them or be knocked out, while crew on space stations may have to shelter in spacecraft to avoid the risk of decompression from punctures. Windows of the space shuttle even had to be replaced after being hit by flecks of paint travelling in orbit.
Collisions with large bodies are also a major concern. The first collision between two spacecraft took place in 2009 when a defunct satellite hit an operational communications satellite, destroying both and releasing thousands of fragments into space.
These fragments can produce further fragments if they hit other satellites, bringing the world closer to a situation known as a Kessler Syndrome. Named after NASA scientist Donald Kessler, he predicted that once space pollution is high enough, debris caused by collisions will grow exponentially, much faster than it falls out of orbit.
Eventually, this would form a debris belt around the Earth which would make any space activities in LEO very difficult, if not impossible.
It's also possible that objects in orbit could simply fall out of the sky. While spacecraft are meant to be burnt up in the atmosphere over uninhabited areas, this doesn't always happen.
The exact risks of falling debris are difficult to calculate, but a 2022 Nature Astronomy paper estimates that there is as much as a 10% chance that an uncontrolled rocket re-entry could cause one or more casualties in the next decade.
While the United Nations recommends that satellites should be removed from orbit when their work is done, these guidelines are voluntary and have been followed in different ways. However, growing concern over the impact of space debris means that modern satellites are now starting to be built with disposal in mind.
For instance, they may contain additional fuel which allows them to be pushed into a disposal orbit at the end of their lives. But when this doesn't work, or for older satellites, other technologies are being developed.
In 2018, an experimental satellite was captured a piece of space debris with a net. Other techniques including spacecraft with arms and tentacles have also been proposed, but are unlikely to begin work any time before the end of the decade.
Implementing a treaty that makes the producers and users of satellites responsible for cleaning them up could help to stem the flow of space pollution until clean-up spacecraft can be developed.
Melissa Quinn, a co-author of the letter and Head of Spaceport Cornwall, adds, 'By comparing how we have treated our seas, we can be proactive before we damage the use of space for future generations.'
'Humanity needs to take responsibility for our behaviours in space now, not later. I encourage all leaders to take note, to recognise the significance of this next step and to become jointly accountable.'