Space junk is raining from the sky. Who's responsible when it hits the Earth?

In March 2022, a couple liv‐ ing in the rural town of São Mateus do Sul, Brazil, were shocked to find a 600-kilo‐ gram piece of smashed metal lying just 50 metres from their home.

Four months later, two Australian sheep farmers found a strange, black object that appeared to have em‐ bedded itself in a field.

Then last week, a farmer in Ituna, Sask., found a simi‐ lar object in his wheat field.

Alien invasion? Nope. All pieces of SpaceX debris that had fallen from the sky.

In the past, these events were rare. Instead, it was of‐ ten said that because our planet is more than 70 per cent ocean, the chances of space debris reaching the ground in a populated area were slim.

While that is still largely true, the chances may be on the rise, said Cassandra Steer, the deputy director of mission specialists at Aus‐ tralian National University's Institute for Space.

WATCH | Saskatchewan farmer finds part of a SpaceX rocket in his field:

"The odds are increasing just because of the amount of space traffic that we are creating," she said. "I mean, in the first 50 years of [space‐ flight] since 1957, when Sput‐ nik was launched, … there were something like 2,000 launches in total.

"These days, we're seeing 1,000 launches per year."

This leads to a big ques‐ tion: Who is responsible for this space debris?

The answer is compli‐ cated. There are a few United Nations agreements in place, but for the most part, it's rare for any one country to take another country to interna‐ tional court over space junk.

Space law

Yes, space law is a thing. The Outer Space Treaty, of which Canada is a signatory, was adopted in 1967 to gov‐ ern the peaceful use of space. It says that countries are liable for any damage caused by space objects they've launched. Commerci‐ al activities are covered by the treaty's Liability Conven‐ tion, Steer said.

"The Liability Convention says if there's damage caused on Earth, or in the air, then it's absolute liability," she said. "In other words, you don't have to prove faults, you just have to figure out where this debris came from."

That convention was put to the test in 1978, when a Soviet nuclear satellite called Cosmos 954 re-entered Earth's atmosphere and ex‐ ploded over Northern Cana‐ da, scattering radioactive de‐ bris from present-day Nunavut to northern Alberta. The Canadian government spent more than $14 million CAD in cleanup efforts.

Canada used the Liability Convention to request $4.4 million in compensation from the Soviet Union. In the end, it received $3 million.

In addition to physical damage, countries could po‐ tentially seek compensation for economic costs that come from planes or ships being forced to divert due to debris re-entry, said Ewan Wright, a PhD candidate at the Univer‐ sity of British Columbia studying the sustainability of the outer space environ‐ ment.

Geopolitical tensions can also influence how countries respond to such incidents, he said.

"The states are wary of setting a precedent because, you know, last month it was U.S. debris hitting Canada. But what if it was Canadian debris hitting China?"

In response to last week's incident, the Canadian Space Agency said, "We are working with our partners at Global Affairs Canada and Depart‐ ment of National Defence on the management of space debris."

There might not be any li‐ ability issues to sort out in this particular case. That's because liability hangs on one word: damage.

And since no damage was done, the U.S. - the country where the debris originated has no real obligation.

A growing problem

What fell in Barry Sawchuk's Saskatchewan field was part of a private SpaceX mission called Axiom-3.

Many people are aware that SpaceX returns the first stage of their rockets to be reused again and again. But there is also a second stage to those rockets, and in some cases - such as with the Ax‐ iom missions and resupply missions to the International Space Station (ISS) - a trunk that holds pressurized cargo. Both of those are expected to fall out of orbit on their own and burn up completely as they re-enter the Earth's atmosphere.

But tell that to Sawchuk. Samantha Lawler, an as‐ sociate professor of as‐ tronomy at the University of Regina who keeps a close eye on satellites and their orbits, said it's concerning that the Saskatchewan debris made it to Earth.

"The farmer found a onehundred-pound piece of junk, four feet by six feet," she said. "It's huge. So yeah, clearly it is not burning up, and others in the area have found other pieces, too."

Part of that may be ex‐ plained by the materials used in the rockets - like carbon fi‐ bre, which was used in that SpaceX trunk. While alumin‐ um will burn up fairly well, carbon fibre doesn't.

This isn't just a SpaceX problem. In 2023, a massive cylindrical object washed up on shore in Western Aus‐ tralia. The Australian Space Agency reported that it was part of a launch vehicle from India's space agency.

There have also been inci‐ dents involving space junk from China. In 2007, a plane narrowly avoided being hit by Russian space debris. And last month, a piece of space junk from the ISS that was expected to burn up ended up slamming through the roof and two floors of a Flori‐ da home.

Chances of being hit

And that's what's most concerning: that one day de‐ bris will hit a plane or some‐ one on the ground.

Aaron Boley is an asso‐ ciate professor at UBC's physics and astronomy de‐ partment and co-director at the Outer Space Institute, a group of experts dedicated to space exploration. He's been crunching the numbers on orbital debris re-entering Earth's atmosphere.

"There's a lot of work that's been done on this. And people have been kind of screaming and pounding things and saying, 'Look, you can't just keep dropping things thinking it's not going to matter,'" he said.

He's deeply concerned that people are looking the other way.

"[NASA] said it was going to entirely demise and ablate in the atmosphere and in‐ stead somebody had some‐ thing that went through their roof, went through the first floor, went through the next floor," he said. "And so there are all these assumptions that I think we are seeing being challenged just be‐ cause there's so much activ‐ ity taking place right now."

For the most part, space companies and agencies are responsible for the end of life of their satellites and rockets. For some, that means allow‐ ing them to gradually orbit at lower and lower altitudes un‐ til they reach a sort of "grave‐ yard" zone around the Earth. Others use their craft's re‐ maining fuel to do a con‐ trolled de-orbit.

But then there are those spent rocket stages that are left to orbit Earth. The planet is always pulling them down, so eventually their orbits "de‐ cay" and they fall back down, and they don't always burn up in the atmosphere when they do.

So what are the chances of space debris crashing into a person?

"We estimate the chance of somebody getting hit by one of the rocket bodies over the next 10 years to be about 20 to 30 per cent," PhD can‐ didate Wright said. "So that worked out to about a three or four per cent chance each year that someone, some‐ where will get hit by a piece of space debris."

Part of that also has to do with how much our popula‐ tion has increased since the start of the space program.

With a record number of launches every year, the risk is only going to grow, Wright said.

"We're putting thousands of satellites up and nothing is really being done about this re-entry issue. And even if we stop launching today, there would still be space debris that comes down over the next century."