How space junk puts space programs and our planet at risk

Early last week, Victorians woke to a strange sight just before dawn – a bright light was hurtling across the sky, but it wasn’t a meteor.

The strange shower of sparks was actually space junk from one of Elon Musk’s* satellites.

With many of our modern-day conveniences relying on satellite technology, space junk has started to litter the orbital* space around our planet – and it’s getting worse over time.

WHAT IS SPACE JUNK?

Space junk, or orbital debris*, is any human-made object no longer serving a purpose that is stuck in space. Usually old, broken satellites, pieces of spacecraft, or even tiny flecks of paint, the junk travels at extremely high speeds and is stuck in orbit around the Earth.

In the case of the mystery light over Melbourne last week, Observational Astronomer Associate Professor Michael Brown said there were “a couple of giveaway signs” it was space junk.

“It’s coming in almost horizontally and it’s going a lot slower than a meteor, and that means lots of people were able to get their phones out and record it,” he said the morning it was spotted.

“It was slowly breaking up into pieces, so it was definitely space junk this morning. I talked to an expert in space situational awareness* and he let me know that it’s one of Elon Musk’s Starlinks 5103.

“Satellites move in predictable orbits. So, exactly where specific satellites are and when is very well known and this satellite has had an orbit that’s been decaying* for a while now.”

HOW MUCH SPACE JUNK IS THERE?

Numbers vary depending on which space agency you ask.

According to NASA, there are more than 25,000 pieces of space junk larger than 10cm known to be orbiting the Earth, as well as an estimated 500,000 pieces of space junk between one and 10cm in diameter.

The European Space Agency (ESA), however, estimates there are more than 1.2 million pieces of space debris larger than 1cm that could cause catastrophic damage in a collision, with over 50,000 of those thought to be bigger than 10cm.

Most space junk enters Low Earth Orbit* (LEO) which has been described on NASA’s official site as “an orbital space junk yard” where there are thought to be close to 6,000 tonnes of debris circulating.

WHY DOES IT POSE A PROBLEM?

Given the high speed at which it travels, about 27,000km/hr, space junk can be dangerous to crewed spacecraft and working satellites if it collides with them.

Prof Brown said space junk also poses an environmental impact upon re-entry.

Starlink satellites, such as the one that lit up the sky over Melbourne, provide internet access to the population and only remain in orbit for several years, Prof Brown said, and they come down very regularly.

“There are many thousands of those satellites up in orbit right now, and they’re coming down almost daily across the globe,” he said.

“That actually may have environmental consequences, because all the bits that satellites are made of are burning up in the upper atmosphere,” he said.

“And as we know from the ozone layer, the upper atmosphere is actually important for the health of the planet and thus on the ground.”

WHY IS SPACE JUNK SET TO GROW?

Given their volume and the fact they exist in LEO, Prof Brown said space junk re-entries would become significantly more common going forward.

“Because they’re trying to directly communicate with relatively small receivers on Earth, they’re in low orbits — and low orbits that are only, say, 500km altitude or so, experience a lot of drag from the Earth’s atmosphere,” Prof Brown said.

“So they only stay in orbit for a limited time.”

DO SPACE COMPANIES HAVE TO CLEAN UP THEIR OWN JUNK?

According to NASA, there are no international laws that require space companies to clean up the debris currently littering the LEO.

However, there are space mitigation* guidelines set by the UN that advise satellites should be retired after 25 years. The ESA introduced a new standard of taking rocketing aircraft out of orbit within five years for its own space activities. ESA has also set a Zero Debris Approach to limit the production of orbital Earth and lunar debris* by 2030. The US Federal Communications Commission (FCC) also requires US licensed satellite operators in LEO to deorbit* their satellites within five years of completing their missions.

ESA Space Environment Report 2025 states there has been an increased level of satellites and rocket re-entries in line with efforts to reduce space junk, with intact satellites or rocket bodies re-entering the Earth’s atmosphere on average more than three times a day.

Despite the increase in re-entries, “not enough satellites” have been leaving orbit at the end of their working lives and the problem of space congestion has grown.

WHAT DOES THE FUTURE HOLD?

Without better methods for cleaning up space junk, experts warn existing orbits could become too unstable and unsafe to use, putting our future space programs at risk.

Kessler syndrome describes a scenario where there are so many pieces of debris in LEO that the environment could lead to a chain reaction of collisions causing more collisions leaving space unusable for generations.

WATCH THE VIDEO OF STARLINK SPACE JUNK OVER MELBOURNE

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GLOSSARY

Elon Musk: the billionaire entrepreneur who leads xAI, Tesla, Inc and space exploration company SpaceX

orbital: the space around Earth where objects are drawn into orbit

debris: bits and pieces of things

situational awareness: the practice of predicting and tracking the paths of the many human made and natural objects in orbit

decaying: breaking apart

Low Earth Orbit: the region of space closest to Earth where objects orbit extremely quickly, taking about 90 minutes to zoom around the planet, usually from about 160km to 2000km above Earth’s surface

mitigation: taking steps to address a problem

lunar debris: space junk left on the moon

deorbit: take something out of orbit

EXTRA READING

Astronauts journey to next frontier

Have we found a second Earth?

Space junk crash leaves double crater in moon

QUICK QUIZ

What “telltale signs” revealed the mystery light over Melbourne was a Starlink satellite?

What is another name given to space junk orbiting the Earth?

Which field of orbit does most space junk enter?

Why does space junk pose a risk to future space travel?

Why have there been more satellite re-entries in recent years, according to the ESA?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES

1. Space junk speech writing

Choose from the two options below and write a speech about space junk:

Option 1 – You are the rich CEO of a satellite company and you want to convince the public and governments that companies should have no responsibility whatsoever for cleaning up their space junk.

Option 2 – You are an environmentalist and you want to convince the public and governments that satellite companies should be made to take full responsibility for cleaning up their space junk.

You should think about the speech maker’s motivations and ensure that you are providing detailed reasons to persuade your audience.

Time: allow 30 minutes to complete this activity

Curriculum Links: English; Science; Sustainability

2. Extension

Practise your speech “in character” as the CEO or environmentalist. You may create costumes or props to use if you have the time and resources. Then film yourself delivering the best possible version of your speech.

Time: allow 30+ minutes to complete this activity

Curriculum Links: English; Drama; Media Arts

VCOP ACTIVITY

BAB it!

Show you have read and understood the article by writing three sentences using the connectives “because’’, “and”, and “but” (BAB). Your sentences can share different facts or opinions, or the same ones but written about in different ways.