A piece of a SpaceX Falcon 9 rocket slammed into the Moon on August 5 after drifting through space for more than 18 months. The high-speed collision kicked up a plume of debris and gouged out a fresh crater roughly 18 metres wide and less than three metres deep.
Images from Nasa’s Lunar Reconnaissance Orbiter (LRO), released on August 18, showed the impact site ringed by bright rays of excavated lunar material. No intact wreckage was detected.
The rocket had launched in January 2025 carrying two lunar landers, Firefly Aerospace’s Blue Ghost 1 and Japanese company ispace’s Resilience. Its first-stage booster returned safely to Earth. The upper stage stayed behind to push the landers towards their target, and the gravitational pull of the Sun, Earth and Moon, along with solar radiation pressure, gradually bent its trajectory until it hit the lunar surface.
The episode renewed a longer-running debate about what humans leave behind in space. The Moon, according to space-agency mission records, already carries more than 200 tonnes of material from past human missions, some of it abandoned, some deliberately placed. Above Earth, though, tens of thousands of objects now circle the planet at speeds high enough to make even a paint fleck lethal.
Space debris means human-made objects in space that no longer serve a useful purpose. That covers defunct satellites, spent rocket stages, fragments from explosions or collisions, and much smaller pieces such as paint flakes and shards of metal.
The scale is difficult to visualise. The European Space Agency’s Space Debris Office, whose statistics were last updated on July 31, said more than 7,320 rocket launches since 1957 have placed about 27,490 satellites in Earth’s orbit. Roughly 18,840 remain in space, of which about 16,000 are still functioning. The combined mass of everything humans have left in orbit exceeds 17,000 tonnes, more than twice the iron in the Eiffel Tower.
Space surveillance networks regularly track about 46,590 catalogued objects. ESA estimates a further 1.2 million pieces between 1 cm and 10 cm in size, small enough to escape tracking but large enough to disable a satellite. Another 140 million fragments are smaller than 1 cm, it estimates.
In orbit, the size can be deceiving too. Objects in low Earth orbit travel at roughly 7.8 km per second, or about 28,000 km per hour, and relative velocities in a head-on encounter can reach 14 km per second. At those speeds, even a paint fleck carries the energy of a bullet.
How did it get there?
Some debris is simply hardware nobody removed. Spent rocket stages remain in orbit after delivering their payloads. Satellites die and stay there. Mission hardware, from lens caps to astronaut tools, gets left behind.
Then there are incidents. A rocket stage or satellite can explode because it still contains residual fuel or stored battery energy, ESA said. The space environment degrades components over time, allowing fuel to leak or batteries to short-circuit. One spacecraft can turn into a cloud of pieces moving in different directions.
ESA has recorded more than 660 such break-ups, explosions, collisions or anomalous events.
Other debris can come from deliberate destruction. China destroyed its own defunct FengYun-1C weather satellite in an anti-satellite missile test in January 2007, single-handedly increasing the catalogued low-Earth-orbit debris population by about 25% at the time. According to tracking data compiled by KeepTrack from the US Space Surveillance Network, 3,534 fragments have been catalogued from that test, of which about 2,318 were still in orbit as of August.
India carried out its own kinetic anti-satellite test, Mission Shakti, in March 2019, and destroyed the Microsat-R satellite at an altitude of about 283 km. Because the intercept happened at a much lower altitude than the Chinese test, most of the debris re-entered the atmosphere within months.
Jim Bridenstine, then Nasa administrator, called it “a terrible thing”, saying some fragments had briefly been lofted above the International Space Station (ISS). India’s Defence Research and Development Organisation (DRDO) pushed back and said the test had been designed to minimise debris, and that all fragments would decay within 45 days.
Russia’s most recent such test, in November 2021, destroyed the defunct Kosmos 1408 and produced roughly 1,500 trackable pieces. The strike forced the ISS crew, including two Russian cosmonauts, to shelter in their return capsules.
Collisions can be even more destructive. On February 10, 2009, the operational US Iridium 33 communications satellite struck the defunct Russian Kosmos 2251 over Siberia at a closing speed of about 11.7 km per second, the first known accidental hypervelocity collision between two intact satellites. The crash produced more than 2,000 catalogued fragments, over a thousand of which remain in orbit.
ESA has counted four such confirmed collisions between catalogued objects to date.
In addition, the pressure on low Earth orbit (LEO) has climbed sharply this decade with the deployment of large commercial constellations.
SpaceX’s Starlink accounted for more than 10,700 active satellites in lower LEO as of August 13, according to astronomer Jonathan McDowell’s tracker at planet4589.org. The Eutelsat-owned OneWeb operates around 650. And China’s planned Guowang and Qianfan constellations are ramping towards a combined total in the tens of thousands.
Also read: What is Kessler Syndrome? The growing threat of space junk and its consequences
What if there’s a collision?
An object does not need to be large to cause serious trouble in space.
In May 2016, British astronaut Tim Peake photographed a 7 mm-wide chip in one of the ISS Cupola’s windows. ESA said the damage was probably caused by a paint flake or metal fragment no bigger than a few thousandths of a millimetre across, travelling at orbital speed.
China’s Shenzhou-20 spacecraft was suspected of being struck by a small piece of debris while carrying three astronauts. The impact cracked its viewport window, with the fracture running through the full thickness of the pane, according to the China Manned Space Agency. Chinese officials judged it too risky for the crew to re-enter aboard the damaged capsule, so the astronauts came home aboard Shenzhou-21, and China launched an uncrewed Shenzhou-22 as an emergency replacement.
The ISS has also moved out of the way of debris dozens of times since assembly began in 1998, according to Nasa’s Orbital Debris Program Office. This includes several manoeuvres to avoid fragments from the 2007 FengYun-1C Chinese weather satellite break-up.
In 1978, Nasa scientist Donald Kessler warned in the Journal of Geophysical Research of a chain reaction that now bears his name. As orbital space grows more crowded, one collision creates debris that hits other objects, sparking more crashes. Over time, the snowball effect could pollute popular orbits so heavily that using them becomes too dangerous. The concept applies mainly to low Earth orbit, the region up to about 2,000 km altitude.
Does the junk fall back to Earth?
Eventually, some of it does. Most smaller objects burn up during re-entry, but larger pieces can survive to the ground. Where they fall also matters, specifically when the spacecraft contains hazardous material.
Scientists have started using earthquake sensors to measure this. In a study led by Benjamin Fernando, then of Johns Hopkins University, and Constantinos Charalambous of Imperial College London, researchers reconstructed the re-entry of China’s Shenzhou-15 spacecraft using 125 California seismometers. As the hardware ripped through the air faster than the speed of sound, its sonic booms created ground vibrations. By mapping those vibrations, the team pinned down the object’s exact flight path and break-up point.
Standard radar predictions of re-entry can be inaccurate by thousands of kilometres. In that case, ground sensors can offer a powerful backup.
The Falcon 9 upper stage was in deep space before hitting the Moon. In such cases, hardware left in lunar orbit stays around because the Moon has no atmosphere to drag down or burn up lingering objects.
Also read: Can space junk actually kill you? Scientists explain
Can we clean up?
Humans can mitigate, i.e. avoid adding more debris into the space, or remediate — remove what is already there.
Remediation is a lot more difficult, but engineers are designing tools such as robotic arms, harpoons, capture nets, magnetic tethers and ground-based lasers to nudge debris off course.
A handful of concepts have moved beyond the drawing board.
Japanese company Astroscale flew its ADRAS-J spacecraft in 2024, the first mission to approach and inspect a piece of orbital debris at close range, which — in this case — was a discarded Japanese H-2A rocket upper stage. A follow-on spacecraft, ADRAS-J2, is being built to attempt actual capture and controlled de-orbit.
ESA’s ClearSpace-1 mission is scheduled to launch in 2029 to capture and de-orbit PROBA-1, a satellite launched in 2001. Its original target, a Vespa payload adapter, was replaced after it was hit by other debris. US firm Firefly Aerospace is developing its Elytra spacecraft to track, inspect and de-orbit ageing satellites.
But cleaning up space is not straightforward. There is no practical way today to collect every tiny fragment, and every removal mission has to be designed carefully so that the attempt to remove one dangerous object does not end up creating more debris.
Who is responsible for space junk?
Space is used by governments, international organisations and private industry. A satellite may be launched by one country, operated by a company headquartered in another and eventually become an abandoned object travelling through an orbital environment used by everyone.
Rules for this were written in the 1960s and 1970s.
The 1967 Outer Space Treaty makes states internationally responsible for their national space activities, including those of private firms. The 1972 Convention on International Liability for Damage Caused by Space Objects makes launching states liable for damage caused by their spacecraft. That convention has been formally invoked only once, after the Soviet Kosmos 954 satellite, carrying a nuclear reactor, crashed in Canada’s Northwest Territories in January 1978. Moscow eventually paid Ottawa CAD (Canadian dollar) 3 million.
More recent guidelines have tried to address the problem directly. The Inter-Agency Space Debris Coordination Committee, whose members include the Indian Space Research Organisation (Isro), issued mitigation guidelines recommending that satellites be moved out of protected orbits within 25 years of the end of their operational life. In 2019, the UN Committee on the Peaceful Uses of Outer Space adopted a broader set of long-term sustainability guidelines.
Regulators have tightened the rules since. The US Federal Communications Commission in September 2022 cut the 25-year post-mission disposal window to five years for satellites in low Earth orbit licensed through the US, a change that took effect in September 2024. ESA has adopted a similar five-year threshold as part of its own Zero Debris Approach, which targets no new debris from ESA missions by 2030.
Also read: Florida resident describes moment ‘space debris’ ripped through his home: ‘It almost hit my son’
What India is doing about it
India has hardware in orbit that is no longer operational. In March, the department of space said 129 trackable pieces of debris originating from Indian satellite missions were then in orbit, including defunct satellites, spent rocket bodies and fragments from an earlier in-orbit break-up.
The government’s Debris Free Space Mission aims to eliminate new debris from India and its licensed private missions by 2030. To meet that target, Isro is carrying extra fuel on rockets to push dead satellites back down to burn up in the atmosphere.
Through its Network for Space Object Tracking and Analysis, or NETRA, India also monitors orbital traffic to predict re-entries and avoid collisions. Isro is developing robotic arms and testing precise space manoeuvres, such as its SpaDeX docking mission, to build the technology needed to approach, inspect and remove orbiting debris safely.
Can we keep space usable?
Space remains useful. Satellites underpin communications, navigation, weather forecasting, Earth observation, climate research and human spaceflight. The orbital environment, though, is a finite resource in practical terms.
The next frontier is no longer the Earth’s orbit. Falcon 9, which crashed into the Moon, was a reminder that human print is spreading into the space between Earth and the Moon, and onto the lunar surface too.
