At 3 p.m. on 30 December last year, residents of Mukuku village in Makueni county, Kenya, were startled by a loud crash. In the middle of a field lay a mysterious, smouldering metal ring, 2.5 metres across and weighing nearly 500 kilograms. Elsewhere, in western Uganda in May 2023, villagers reported seeing streaks of fire in the sky before debris rained down, scattering wreckage across a 40-kilometre-wide area.

These were no ordinary meteorites — they were remnants of a defunct satellite and spent rocket stage, returning to Earth without warning.

The quest to conquer Earth’s space junk problem

These events are not isolated. Across the world, from Texas to Saudi Arabia, from Cape Town to the Amazon rainforest, objects launched into low Earth orbit (LEO) are now falling back to Earth. Some burn up harmlessly in the atmosphere, but others — especially those made of titanium and heat-resistant space-age alloys — survive re-entry and slam into the ground, sometimes in populated areas.

The problem is getting worse. With the rapid expansion of commercial space flight, thousands of satellites are being launched each year. Yet few owners have plans to remove them from orbit in a controlled way.

Everyone, everywhere — on Earth’s surface, flying in aeroplanes, as well as in space — is increasingly at risk from these projectiles¹.

Space-faring nations and companies must urgently address this threat. The uncontrolled re-entry of space debris is not just a nuisance — it is a legal, environmental and potentially catastrophic problem. Without fresh policies and mitigation strategies, it is only a matter of time before one of these incidents leads to a loss of life.

A growing problem above

Low Earth orbit, the region of space stretching from 160 km to 2,000 km above Earth’s surface, is the most congested orbital zone. It is home to imaging satellites, weather and communications constellations and space stations such as the International Space Station (ISS).

It is also the most debris-laden part of space, harbouring more than 6,000 tonnes of human-made objects. The World Economic Forum predicts that by 2030, more than 60,000 satellites will have been launched, the majority of which are destined to become debris^2,3.

Four steps to global management of space traffic

Most satellite re-entries are uncontrolled. Some space agencies deliberately steer defunct satellites into the ocean. However, many operators simply leave them to decay naturally, with no certainty about where they will land. Any location on Earth could be in the firing line.

As objects in LEO experience atmospheric drag, they gradually slow down and spiral back to Earth. Smaller fragments burn up during re-entry, but larger pieces — rocket stages, fuel tanks and satellite components — often survive, crashing to Earth at speeds of hundreds of kilometres per second. The energy released by their impacts can be equivalent to that of a small missile⁴. The higher the re-entry speed, the further debris can spread.

Predicting crash sites is extremely difficult. When an object falls from space, its path to Earth isn’t a straight line or even smooth. Predicting where it will land involves complex calculations and many factors, including Earth’s rotation, gravity, winds and the object’s initial speed and altitude⁵. Mathematical models, such as NASA’s Object Reentry Survival Analysis Tool and simplified general perturbations models, can be used to estimate the track of decaying orbital debris.

History has repeatedly shown that crises are often ignored until they escalate into disasters. Space debris is no exception, and failing to address it urgently could have catastrophic consequences. Imagine a large satellite, weighing several tonnes, re-entering Earth’s atmosphere without warning. Unlike the controlled descent of the Mir space station in 2001, this object might well veer off course and crash into a city. The devastation would be catastrophic, bringing legal, political and financial chaos.

The risks extend beyond ground impacts. A major — and rarely discussed — concern is a potential collision between a falling piece of debris and commercial aircraft. At any given time, more than 10,000 aeroplanes are in the air worldwide. The uncontrolled descent of a dense, high-velocity object through busy air corridors could lead to a mid-air disaster. Currently, there are no global protocols to warn pilots or airlines about incoming space debris. In 2022, US airspace was briefly shut down because of an uncontrolled rocket body re-entry. Although such closures are rare, increasing global space activity makes similar incidents more likely, underscoring the need for stricter regulations on debris mitigation and controlled re-entries to prevent future disruptions and safety hazards.

Cascading collision threats

Beyond the immediate threat of falling debris, there’s a looming danger known as Kessler Syndrome². Proposed by NASA scientist Donald Kessler in 1978, this scenario predicts a point at which the density of objects in LEO becomes so high that collisions between them generate more debris, leading to a cascade of further collisions.

This self-perpetuating cycle could render certain orbital regions unusable, posing risks to satellites, space missions and the ISS. As of 2021, there were more than 4,000 active satellites in orbit, with estimates of 600,000 pieces of space junk ranging from 1–10 centimetres in size⁶. On average, one satellite is destroyed each year when it collides with another satellite or piece of debris.

World’s first wooden satellite could herald era of greener space exploration

The growing amount of space debris is no longer a distant or hypothetical threat; it is an immediate danger. European Space Agency (ESA) estimates show that, as of February this year, more than 36,000 objects larger than 10 cm are currently being tracked in Earth’s orbit and more than one million objects between 1 cm and 10 cm are orbiting the planet. Even tiny fragments — many too small to be detected by current tracking systems — can cause huge amounts of damage owing to the sheer velocity at which they travel. The ISS relies on ballistic panels for protection, but shielding alone is not enough. The station’s crew must remain vigilant; spacewalking astronauts are especially vulnerable.

The escalating situation underscores the crucial need for space-traffic management and collision-avoidance strategies to ensure the long-term viability of space exploration and utilization. As orbital congestion worsens, the need for robust tracking, accountability and mitigation strategies becomes undeniable.

Furthermore, sunlight reflected from and the burning up of orbital debris contribute to light pollution, increasingly interfering with views of the night sky from ground-based scientific observatories. For instance, bright trails from SpaceX’s satellite constellations, although not classified as active debris, are hard to miss as they move across the night sky. In January, astronomers mistook a Tesla Roadster, an electric sports car that was launched by SpaceX in 2018 as a stunt, for an asteroid that could potentially threaten Earth. Having to devote global resources to track such an object is wasteful.

The legal black hole