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

In March 2022, a couple living in the rural town of São Mateus do Sul, Brazil, were shocked to find a 600-kilogram 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 embedded itself in a field. 

Then last week, a farmer in Ituna, Sask., found a similar 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 often 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 Australian 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 [spaceflight] since 1957, when Sputnik 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 question: Who is responsible for this space debris?

The answer is complicated. 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 international court over space junk.

Yes, space law is a thing. 

The Outer Space Treaty, of which Canada is a signatory, was adopted in 1967 to govern the peaceful use of space. It says that countries are liable for any damage caused by space objects they've launched. Commercial activities are covered by the treaty's Liability Convention, 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."