Around 140 million pieces of space debris larger than one millimetre are orbiting Earth as a new generation of lunar missions raises urgent questions about sustainability beyond the planet.
Most of the fragments are too small to track but travel fast enough to destroy satellites and create thousands of additional pieces through collisions.
The United Nations Environment Programme (UNEP) has warned that rapidly expanding space activity is leaving an environmental footprint in orbit and within Earth’s atmosphere.
The warning coincides with International Moon Day and a revival in lunar exploration led by governments and private companies.
NASA’s Artemis II mission recently carried four astronauts on a 10-day journey around the Moon as part of plans to establish a long-term human presence on its surface during the 2030s.
China, India, Japan and private space companies are also developing lunar programmes which could substantially increase launches and activity around the Moon.
UNEP Senior Officer Jason Jabbour said:
Decades of rapidly expanding space activity have shown that each launch leaves an environmental footprint and it can take a long time to understand the impact fully. This is why it is so crucial to consider the sustainability of these programmes early on.”
Space sustainability involves carrying out missions without making orbits and lunar environments unusable for future generations.
The 1967 Outer Space Treaty requires countries to avoid harmful contamination while UN guidelines call for debris to be minimised and defunct spacecraft to be removed safely.
Satellites create environmental risks when they reach the end of their working lives and re-enter the atmosphere.
Most burn up during descent which releases aluminium, lithium, copper and other metals into the upper atmosphere.
Scientists have already detected metals from spacecraft in stratospheric particles. Research is under way to understand their potential effects on atmospheric chemistry, cloud formation and the ozone layer.
Abandoned rocket stages create another problem because they can remain in orbit for years before falling back to Earth or fragmenting into thousands of pieces.
Hundreds of tonnes of rockets and spacecraft are estimated to re-enter the atmosphere annually. That volume is expected to rise as operators replace satellites within large constellations.
Collisions and explosions generate some of the most dangerous debris with fragments travelling at around 28,000 kilometres per hour.
Even a tiny object moving at this speed can destroy another spacecraft and trigger a chain of further collisions.
Explosions can be caused by fuel or charged batteries left inside abandoned equipment. Deliberate anti-satellite weapons tests also create dense clouds of debris that can remain in orbit for decades.
UN guidelines urge operators to vent unused propellant and discharge batteries before removing retired satellites and rocket stages from orbit. Since 2022 a growing number of countries have also pledged not to conduct destructive anti-satellite missile tests.
Missions can leave behind bolts, protective covers, lens caps and other small pieces during launches or satellite deployment.
Repeated collisions and erosion also create microscopic particles which form a diffuse cloud around Earth. Scientists believe reflected and scattered sunlight from orbiting material is already increasing night-sky brightness.
Larger or heat-resistant objects can survive re-entry and threaten people or infrastructure. Debris falling into oceans could also damage habitats or introduce hazardous substances into marine ecosystems.
Under the 1972 UN Liability Convention the country commissioning a launch and the country providing the launch territory or facilities can share responsibility for damage caused on Earth.
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