LONDON, July 16 — The space around our planet is getting crowded, and not in a good way. Scientists are increasingly concerned about the growing cloud of debris orbiting Earth—defunct satellites, spent rocket stages, fragments from collisions, and even flecks of paint—that now poses a measurable risk to active spacecraft and, on occasion, to aircraft below. According to the European Space Agency’s Space Environment statistics, as of April 2025, ground-based Space Surveillance Networks regularly track 40,230 artificial objects in orbit above Earth.
But those are just the pieces large enough to be seen from the ground. The real numbers are far bigger.
As of January 2019, researchers estimated that more than 128 million pieces smaller than one centimetre, about 900,000 pieces between one and ten centimetres, and roughly 34,000 pieces larger than ten centimetres were circling the planet. The smallest items—paint flecks, solid rocket exhaust particles—are grouped with natural micrometeoroids and called MMOD, short for Micrometeoroid and Orbital Debris. Space debris has been accumulating since the launch of Sputnik 1 in October 1957.
The problem is what economists call a negative externality: the cost of launching a spacecraft into near-Earth orbit is not fully borne by the launcher or payload owner, but is instead shared by everyone who operates there. Debris from one mission can damage or destroy another.
Several crewed and un-crewed spacecraft have already been hit.
How debris damages spacecraft
The physics is straightforward but sobering. Objects in low Earth orbit travel at enormous speeds, so even tiny particles carry significant kinetic energy. The smallest debris causes damage akin to sandblasting, particularly to delicate surfaces such as solar panels and optics like telescopes or star trackers.
Below an altitude of 2,000 kilometres, the density of debris pieces actually exceeds that of natural meteoroids. Much of that material is dust from solid rocket motors, surface erosion debris like paint flakes.
The two most recent large debris events were the 2007 Chinese antisatellite weapon test and the 2009 satellite collision, both occurring at altitudes between 800 and 900 kilometres. Those breakups added thousands of fragments to the debris population, much of which remains in orbit.
Risks to aviation
The hazard is not confined to space. The volume of reentering debris is increasing. A vivid example occurred after the explosion of SpaceX’s Starship Flight 7 on January 16, 2025.
The US Federal Aviation Administration slowed air traffic in the area where debris was falling, prompting several aircraft to request diversion due to low fuel levels while holding outside the Debris Response Area. The incident highlighted how a single launch failure can ripple into the daily operations of commercial aviation.
What comes next
The measurement, mitigation, and potential removal of debris is now an active area of work for some participants in the space industry. With launch rates rising and the debris population only growing, the question is no longer whether space junk is a problem, but how the world will manage it before the next major collision forces the issue.
