It was an ordinary afternoon, March 7, 2024, until residents in Germany received a warning from the Federal Office of Civil Protection and Disaster Assistance — abbreviated in German as BBK. It warned that fragments of space debris were expected to fly over Germany the following days, March 8-9.

Details were sparse from both the BKK and the European Space Agency.

Authorities expected a palette of nine batteries to reenter the Earth's atmosphere on an uncontrolled trajectory.

The total mass was to be in the region of 2.6 metric tons — the equivalent of 2,600 kilograms (about 5,730 pounds), or, as some have said, the size of a large car.

Most of the battery was expected to burn up on reentry, which is normal. However, it's equally normal for some of these larger bits of space debris to survive and land — usually in the ocean.

And that's exactly what happened on Friday evening. The German military's space monitoring center said the bulk of the debris must have crashed in the Atlantic Ocean a little after 8 p.m. (1900 GMT/UTC). Around an hour earlier, people in some parts of central Germany could see a "bright trail" in the sky that was the falling debris, the agency said.

What's the risk of an uncontrolled reentry to Earth?

The ISS battery pack had a "natural" trajectory between -51.6 degrees south and 51.6 degrees north. Natural trajectory means "uncontrolled" — it is not guided by computers or humans on Earth.

Batteries cannot be navigated like satellites and other spacecraft, so they can only reenter Earth uncontrolled. This made it difficult to predict how the batteries would break up and where they would fall.

But even before most of the debris splashed down in the Atlantic, ESA assured that no one would likely be harmed. "While some parts may reach the ground, the casualty risk — the likelihood of a person being hit — is very low."

In an email to DW, Germany's BBK reiterated ESA's risk assessment, adding only that they could not provide further advice to residents or suggest any protective measures that people could take before the "event" had happened.

The BBK confirmed that the IIS battery pack would fly over Germany more than once before its reentry into the atmosphere. Germany's space monitoring center confirmed this to be the case in a post on X, the social media platform formerly known as Twitter.

In fact, its trajectory took it over most of Europe, Latin America, northeastern Africa, the Middle East, South and Southeast Asia and Australia.

So, should you have worried when the official line is "no" and the risk to human life is considered low?   

How much space junk falls to Earth every year?

According to ESA, space junk reenters the Earth's atmosphere via uncontrolled trajectories almost every week. 

Since the 1960s, the number of space debris events has risen steadily, but in the past few years, the increase has been exponential: ESA's data from December 2023 shows that almost 2,500 bits of space debris fell to Earth in the year before.

In 2023, the number was down again to about 1,500 objects. But given that between the years 1960 and 2000, the so-called "object count" averaged at about 500 bits of debris per annum, we have seen quite a jump.

What kinds of space debris fall to Earth?

About 44 tons or 44,000 kilograms of meteoritic material fall on Earth each day, but about 95% of it burns up.

Most of the space debris that falls to Earth is what's called payload fragmentation debris, objects that have fragmented or been unintentionally released from a spacecraft when an object explodes or collides with another object.

Other common space debris includes rocket mission-related objects, "space objects intentionally released as space debris" after having served their purpose. That includes spent batteries. The ISS battery pack was intentionally released from the space station three years before its reentry in 2024.

Is space debris toxic?

If a satellite falls to Earth, its structure is unlikely to be toxic. But it may contain toxic elements within it. It also depends on where space debris falls.

In a 2021 interview, space debris expert and author of Dr Space Junk vs the Universe,  Alice Gorman, told DW: "Some spacecraft fuels are toxic — hydrazine, for example. There are metals like beryllium and magnesium, they are usually in alloy form, but beryllium is pretty nasty no matter what."  

Some experts are concerned about the effects of these toxic elements, especially as most space debris lands in the ocean. But the effects are not widely researched, said Gorman.

"Salt water can corrode things easily, but we have a million shipwrecks across the world, and shipwrecks generally become habitats [for marine life]," she said. "And the priority really should be what's in orbit. That's by far the bigger risk."

So, how big is the risk of getting hit by space debris?

Experts have estimated that you're 65,000 times more likely to be struck by lightning than to have a bit of space debris fall on your head.

And you're 1.5 million times more likely to die in an accident at home.

You're three times more likely to be hit by a meteorite than space debris, and how often does space rock land on the planet? So, statistically, you should be okay.

This piece was updated to include the space debris crashing into the Atlantic Ocean.

Edited by: Davis VanOpdorp