What is Kessler syndrome?

A US Air Force weather satellite broke up in space last month, shattering into 50 pieces and joining the estimated 130 million bits of "space junk" in the Earth's orbit.

The increasing amount of debris has heightened fears about the "Kessler syndrome". Named after an American astrophysicist called Donald Kessler, it refers to a scenario in which a space junk collision sets off a chain reaction of similar incidents. Experts are divided over how likely such a scenario is, and how much of a threat it poses to Earth.

What is Kessler syndrome?

Although its exact definition is "muddy", said CNN, Kessler syndrome "broadly describes" a chain reaction scenario in which a collision "sends out a plume of fragments" that "in turn smash into other spaceborne objects", creating "more detritus". This "cascading effect" may continue until the Earth's orbit is "so clogged with junk" that it impacts everyday life.

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What effect could it have?

In a worse-case scenario, a "cloud of space junk surrounding the Earth" risks "cutting off operations" for all technology that relies on satellites, such as weather forecasts, GPS and television, said the Daily Mail. Metallic space debris in particular could "disrupt Earth's magnetosphere, exposing all life to deadly cosmic rays".

A Kessler syndrome event "would affect everybody on the planet", said Paul Lynam, an astronomer at the University of California’s Lick Observatory. An "overcrowded orbital space" would also hamper ground-based telescopes and could mean "our dreams of going to the Moon or further would be dashed", said the National Space Centre.

Has it already started?

The "scientific community hasn’t yet reached a consensus about whether the Kessler syndrome has begun, or, if it has not begun, how bad it will be when it starts", said Aerospace America magazine. The International Space Station "hasn't been destroyed, payloads reach deep space unharmed, and we're not trapped on Earth" by debris, so either the "calamity" is not yet "upon us" or we "just don't recognise it".

Space debris already has a total mass of more than 9,300 tonnes, according to the European Space Agency, which says the "probability for catastrophic collisions" will also "grow progressively". Doubling the number of objects in space increases the collision risk by approximately four times.

How big a problem is space junk?

The amount of orbital debris is growing fast, said Ars Technica. The world used to send about 80 to 100 satellites into orbit each year, but that number jumped above 1,000 in 2020, surpassed 2,000 in 2022, and more countries and companies are jumping into the satellite game. According to the Union of Concerned Scientists, as many as 57,000 could be in low-Earth orbit by 2030.

Objects the size of blueberries orbiting the Earth "have the kinetic energy of a falling anvil," while there are "tens of thousands of pieces of trackable debris the size of a softball or larger that have the kinetic energy of a large bomb".

But it's "not all doom and gloom", said the National Space Centre. Leading space scientists are "devising solutions" and prototypes "have already been tested and missions have been scheduled" to "help clean up our orbit". RemoveDebris, a project led by the University of Surrey, successfully captured a shoebox-sized object by "smothering it in a huge net", harpooned another piece of "dummy debris" and will use a "giant membrane" to pull the object towards Earth, so it "burns up safely in our atmosphere".